Table of contents for issue 07, volume 2018, Journal of Cosmology and Astroparticle Physics

The decay of massive particles during inflation generates characteristic signals in the squeezed limit of the primordial bispectrum. These signals are in particular distinctive in the regime of the quasi-single field inflation, where particles are oscillating with masses comparable to the Hubble scale. We apply the investigation to a class of scalar particles that experience a so-called waterfall phase transition in the isocurvature direction driven by the symmetry-breaking mechanism based on the hybrid inflation scenario. With a time-varying mass, a novel shape of oscillatory bispectrum is presented as the signature of a waterfall phase transition during inflation.

Cosmological weak lensing has been a highly successful and rapidly developing research field since the first detection of cosmic shear in 2000. However, it has recently been pointed out in Yoo et al. that the standard weak lensing formalism yields gauge-dependent results and, hence, does not meet the level of accuracy demanded by the next generation of weak lensing surveys. Here, we show that the Jacobi mapping formalism provides a solid alternative to the standard formalism, as it accurately describes all the relativistic effects contributing to the weak lensing observables. We calculate gauge-invariant expressions for the distortion in the luminosity distance, the cosmic shear components and the lensing rotation to linear order including scalar, vector and tensor perturbations. In particular, the Jacobi mapping formalism proves that the rotation is fully vanishing to linear order. Furthermore, the cosmic shear components contain an additional term in tensor modes which is absent in the results obtained with the standard formalism. Our work provides further support and confirmation of the gauge-invariant lensing formalism needed in the era of precision cosmology.

In a previous communication [1] it was shown that a joint analysis of Cosmic Microwave Background (CMB) data and the current measurement of the local expansion rate favours a model with a scale invariant spectrum (HZP) over the minimal ΛCDM scenario provided that the effective number of relativistic degrees of freedom, N_eff, is taken as a free parameter. Such a result is basically obtained due to the Hubble Space Telescope (HST) value of the Hubble constant, H₀ = 73.24 ± 1.74 km . s⁻¹.Mpc⁻¹ (68% C.L.), as the CMB data alone discard the HZP+N_eff model. Although such a model is not physically motivated by current scenarios of the early universe, observations pointing to a scale invariant spectrum may indicate that the origin of cosmic perturbations lies in an unknown physical process. Here, we extend the previous results performing a Bayesian analysis using joint CMB, HST, and Baryon Acoustic Oscillations (BAO) measurements. In order to take into account the well-known tension on the value of the fluctuation amplitude parameter, σ₈, we also consider Cluster Number counts (CN) and Weak Lensing (WL) data. We use two different samples of BAO data, which are obtained using two-point spatial (BAO 2PCF) and angular (BAO 2PACF) correlation functions. Our results show that the joint CMB+HST+WL+NC dataset favor the extensions of the ΛCDM model over its minimal parameterization. Also, analysis with the BAO 2PCF always discard the HZP+N_eff model with respect to standard scenario, whereas the combinations using BAO 2PACF favor the former model. We, therefore, find that all dataset disfavor the ΛCDM model with respect to the HZP+N_eff extension, the only exception being the joint analysis with BAO (2PCF).

With the Planck 2015 result, most of the well known canonical large field inflation models turned out to be strongly disfavored. Axion inflation is one of such models which is becoming marginalized with the increasing precession of CMB data. In this paper, we have shown that with a simple Galileon type modification to the marginally favored axion model calling G-axion, we can turn them into one of the most favored models with its detectable prediction of r and n_s within its PLANCK 1σ  range for a wide range of parameters. Interestingly it is this modification which plays the important role in turning the inflationary predictions to be independent of the explicit value of axion decay constant f. However, dynamics after the inflation turned out to have a non-trivial dependence on f. For each G-axion model there exists a critical value of f_c such that for f>f_c we have the oscillating phase after inflation and for f<f_c we have non-oscillatory phase. Therefore, we obtained a range of sub-Planckian value of model parameters which give rise to consistent inflation. However for sub-Planckian axion decay constant the inflaton field configuration appeared to be singular after the end of inflation. To reheat the universe we, therefore, employ the instant preheating mechanism at the instant of first zero crossing of the inflaton. To our surprise, the instant preheating mechanism turned out to be inefficient as opposed to usual non-oscillatory quintessence model. For another class of G-axion model with super-Planckian axion decay constant, we performed in detail the reheating constraints analysis considering the latest PLANCK result.

We investigate the length of the period of validity of a classical description for the cosmic axion field. To this end, we first show that we can understand the oscillating axion solution as expectation value over an underlying coherent quantum state. Once we include self-interaction of the axion, the quantum state evolves so that the expectation value over it starts to deviate from the classical solution. The time-scale of this process defines the quantum break-time. For the hypothetical dark matter axion field in our Universe, we show that quantum break-time exceeds the age of the Universe by many orders of magnitude. This conclusion is independent of specific properties of the axion model. Thus, experimental searches based on the classical approximation of the oscillating cosmic axion field are fully justified. Additionally, we point out that the distinction of classical nonlinearities and true quantum effects is crucial for calculating the quantum break-time in any system. Our analysis can also be applied to other types of dark matter that are described as classical fluids in the mean field approximation.

Galactic magnetic field (GMF) and secondary cosmic rays (CRs) (e.g. ¹⁰beryllium, boron, antiproton) are important components to understand the propagation of CRs in the Milky Way Galaxy. Realistic modeling of GMF is based on the Faraday rotation measurements of various Galactic and extragalactic radio sources and synchrotron emission from CR leptons in the radio frequency range, thereby providing information of halo height. On the other hand, diffusion coefficient and halo height are also estimated from the ¹⁰Be/⁹Be and B/C ratios. Moreover, density distribution of gaseous components of interstellar medium (ISM) also plays an important role as secondary CRs are produced due to interaction of primary CRs with the gaseous components of ISM . We consider mainly molecular, atomic, and ionized components of hydrogen gas for our study. Recent observations and hydrodynamical simulations provide new forms of density profiles of hydrogen gas in Milky Way Galaxy. In the DRAGON code, we have implemented our chosen density profiles, based on realistic observations in radio, X-ray and γ-ray wavebands, and hydrodynamical simulations of interstellar hydrogen gas to study the variation in the height of the halo required to fit the observed CR spectra. Our results show the halo height (z_t) varies in the range of 2 to 6 kpc for the density profiles considered in our work.

The current concordance model of cosmology is dominated by two mysterious ingredients: dark matter and dark energy. In this paper, we explore the possibility that, in fact, there exist two dark-energy components: the cosmological constant Λ, with equation-of-state parameter w_Λ=−1, and a 'missing matter' component X with w_X=−2/3, which we introduce here to allow the evolution of the universal scale factor as a function of conformal time to exhibit a symmetry that relates the big bang to the future conformal singularity, such as in Penrose's conformal cyclic cosmology. Using recent cosmological observations, we constrain the present-day energy density of missing matter to be Ω_X,0=−0.034 ± 0.075. This is consistent with the standard ΛCDM model, but constraints on the energy densities of all the components are considerably broadened by the introduction of missing matter; significant relative probability exists even for Ω_X,0 ∼ 0.1, and so the presence of a missing matter component cannot be ruled out. As a result, a Bayesian model selection analysis only slightly disfavours its introduction by 1.1 log-units of evidence. Foregoing our symmetry requirement on the conformal time evolution of the universe, we extend our analysis by allowing w_X to be a free parameter. For this more generic 'double dark energy' model, we find w_X = −1.01 ± 0.16 and Ω_X,0 = −0.10 ± 0.56, which is again consistent with the standard ΛCDM model, although once more the posterior distributions are sufficiently broad that the existence of a second dark-energy component cannot be ruled out. The model including the second dark energy component also has an equivalent Bayesian evidence to ΛCDM, within the estimation error, and is indistuingishable according to the Jeffreys guideline.

A key prediction of the standard cosmological model—which relies on the assumption that dark matter is cold, i.e. non-relativistic at the epoch of structure formation—is the existence of a large number of dark matter substructures on sub-galactic scales. This assumption can be tested by studying the perturbations induced by dark matter substructures on cold stellar streams. Here, we study the prospects for discriminating cold from warm dark matter by generating mock data for upcoming astronomical surveys such as the Large Synoptic Survey Telescope (LSST), and reconstructing the properties of the dark matter particle from the perturbations induced on the stellar density profile of a stream. We discuss the statistical and systematic uncertainties, and show that the method should allow to set stringent constraints on the mass of thermal dark matter relics, and possibly to yield an actual measurement of the dark matter particle mass if it is in the 𝒪(1) keV range.

An excess of gamma rays has been identified at the centre of the Milky Way, and annihilation of dark matter has been posited as a potential source. This hypothesis faces significant challenges: difficulty characterizing astrophysical backgrounds, the need for a non-trivial adiabatic contraction of the inner part of the Milky Way's dark matter halo, and recent observations of photon clustering, which suggest that the majority of the excess is due to unresolved point sources. Here we point out that the apparent point-like nature of the emission rules out the dark matter interpretation of the excess entirely. Attempting to model the emission with dark matter point sources either worsens the problem with the inner slope, requires an unrealistically large minihalo fraction toward the Galactic Centre, or overproduces the observed emission at higher latitudes.

Vacuum bubbles may nucleate and expand during the cosmic inflation. When inflation ends, the bubbles run into the ambient plasma, producing strong shocks followed by underdensity waves, which propagate outwards. The bubbles themselves eventually form black holes with a wide distribution of masses. It has been recently suggested that such black holes may account for LIGO observations and may provide seeds for supermassive black holes observed at galactic centers. They may also provide a significant part or even the whole of the dark matter. We estimate the spectral μ-distortion of the CMB induced by expanding shocks and underdensities. The predicted distortions averaged over the sky are well below the current bounds, but localized peaks due to the largest black holes impose constraints on the model parameters.

As opposed to Wald's cosmic no-hair theorem in general relativity, it is shown that the Horndeski theory (and its generalization) admits anisotropic inflationary attractors if the Lagrangian depends cubically on the second derivatives of the scalar field. We dub such a solution as a self-anisotropizing inflationary universe because anisotropic inflation can occur without introducing any anisotropic matter fields such as a vector field. As a concrete example of self-anisotropization we present the dynamics of a Bianchi type-I universe in the Horndeski theory.

Heavy scalar fields can undergo an instability during inflation as a result of their kinetic couplings with the inflaton. This is known as the geometrical destabilization of inflation, as it relies on the effect of the negative curvature of the field-space manifold overcoming the stabilizing force of the potential. This instability can drive the system away from its original path in field space into a new inflationary attractor, a scenario that we dub sidetracked inflation. We study this second phase and its observable consequences in several classes of two-field models. We show that cosmological fluctuations exhibit varied behaviours depending on the potential and the field space geometry, and that they can be captured by single-field effective theories with either a modified dispersion relation, a reduced speed of sound, or an imaginary one—the latter case describing a transient tachyonic growth of the fluctuations. We also numerically calculate the bispectrum with the transport approach, finding large non-Gaussianities of equilateral and orthogonal shapes. In the hyperbolic geometry the potentials of our models present a pole at the boundary of the Poincar&apos;e disk and we discuss their relationships with α-attractors.

We discuss the cosmology of models in which the standard model Yukawa couplings depend on scalar field(s), often referred to as flavons. We find that thermal corrections of the flavon potential tend to decrease the Yukawa couplings, providing an important input to model-building. Working in the specific framework of Froggatt-Nielsen models, we compute the abundance of flavons in the early universe generated both via freeze-in and from coherent oscillations induced by thermal corrections to their potential, and discuss constraints on flavon models from cosmology. We find that cosmology places important constraints on theories containing flavons even for regions of parameter space inaccessible to collider searches.

Ongoing experimental efforts in Antarctica seek to detect ultra-high energy neutrinos by measurement of radio-frequency (RF) Askaryan radiation generated by the collision of a neutrino with an ice molecule. An array of RF antennas, deployed either in-ice or in-air, is used to infer the properties of the neutrino. To evaluate their experimental sensitivity, such experiments require a refractive index model for ray tracing radio-wave trajectories from a putative in-ice neutrino interaction point to the receiving antennas; this gives the degree of signal absorption or ray bending from source to receiver. The gradient in the density profile over the upper 200 meters of Antarctic ice, coupled with Fermat's least-time principle, implies ray “bending” and the existence of “forbidden” zones for predominantly horizontal signal propagation at shallow depths. After re-deriving the formulas describing such shadowing, we report on experimental results that, somewhat unexpectedly, demonstrate the existence of electromagnetic wave transport modes from nominally shadowed regions. The fact that this shadow-signal propagation is observed both at South Pole and the Ross Ice Shelf in Antarctica suggests that the effect may be a generic property of polar ice, with potentially important implications for experiments seeking to detect neutrinos.

Modeling the Point Spread Function (PSF) of wide-field surveys is vital for many astrophysical applications and cosmological probes including weak gravitational lensing. The PSF smears the image of any recorded object and therefore needs to be taken into account when inferring properties of galaxies from astronomical images. In the case of cosmic shear, the PSF is one of the dominant sources of systematic errors and must be treated carefully to avoid biases in cosmological parameters. Recently, forward modeling approaches to calibrate shear measurements within the Monte-Carlo Control Loops (MCCL) framework have been developed. These methods typically require simulating a large amount of wide-field images, thus, the simulations need to be very fast yet have realistic properties in key features such as the PSF pattern. Hence, such forward modeling approaches require a very flexible PSF model, which is quick to evaluate and whose parameters can be estimated reliably from survey data. We present a PSF model that meets these requirements based on a fast deep-learning method to estimate its free parameters. We demonstrate our approach on publicly available SDSS data. We extract the most important features of the SDSS sample via principal component analysis. Next, we construct our model based on perturbations of a fixed base profile, ensuring that it captures these features. We then train a Convolutional Neural Network to estimate the free parameters of the model from noisy images of the PSF. This allows us to render a model image of each star, which we compare to the SDSS stars to evaluate the performance of our method. We find that our approach is able to accurately reproduce the SDSS PSF at the pixel level, which, due to the speed of both the model evaluation and the parameter estimation, offers good prospects for incorporating our method into the MCCL framework.

We incorporate the effects of redshift space distortions and non-linear bias in time-sliced perturbation theory (TSPT). This is done via a new method that allows to map cosmological correlation functions from real to redshift space. This mapping preserves a transparent infrared (IR) structure of the theory and provides us with an efficient tool to study non-linear infrared effects altering the pattern of baryon acoustic oscillations (BAO) in redshift space. We give an accurate description of the BAO by means of a systematic resummation of Feynman diagrams guided by well-defined power counting rules. This establishes IR resummation within TSPT as a robust and complete procedure and provides a consistent theoretical model for the BAO feature in the statistics of biased tracers in redshift space.

We study anisotropic inflationary solutions in massive Gauge-flation. We work with the theory in both the Stueckelberg and dynamical symmetry-breaking limits and demonstrate that extended periods of accelerated anisotropic expansion are possible. In the case of dynamical symmetry breaking, we show that spacetime can transition from isotropic quasi-de Sitter space to an accelerating Bianchi spacetime due to a rolling Higgs field—the spacetime can develop hair. Similarly, symmetry restoring transitions are possible from accelerating Bianchi spacetime to quasi-de Sitter space —the spacetime can lose its hair. These transitions can be arranged to occur quickly, within an e-folding or so, or over tens of e-folds.

We calculate the diffusion coefficients of charged cosmic rays (CR) propagating in regular and turbulent magnetic fields. If the magnetic field is dominated by an isotropic turbulent component, we find that CRs reside too long in the Galactic disc. As a result, CRs overproduce secondary nuclei like boron for any reasonable values of the strength and the coherence length of an isotropic turbulent field. We conclude therefore that the propagation of Galactic CRs has to be strongly anisotropic because of a sufficiently strong regular field and/or of an anisotropy in the turbulent field. As a consequence, the number of sources contributing to the local CR flux is reduced by a factor 𝒪(100) compared to the case of isotropic CR diffusion.

Using the consistency relation in Fourier space, we derive the observed galaxy bispectrum from single-field inflation in the squeezed limit, in which one of the three modes has a wavelength much longer than the other two. This provides a non-trivial check of the full computation of the bispectrum based on second-order cosmological perturbation theory in this limit. We show that gauge modes need to be carefully removed in the second-order cosmological perturbations in order to calculate the observed galaxy bispectrum in the squeezed limit. We then give an estimate of the effective non-Gaussianity due to general-relativistic lightcone effects that could mimic a primordial non-Gaussian signal.

We consider the power spectrum of a biased tracer observed in a finite volume in the presence of a large-scale overdensity and tidal fields. Expanding both the observed power spectrum and the source fields (linear power spectrum, scalar overdensity and tidal field tensor) in spherical harmonics, we explicitly confirm that each (ℓ,m) source generates just the corresponding (ℓ,m) modes of power spectrum in real space. In redshift space, each (ℓ,m) source additionally couples only to (ℓ+2n,m) modes of tracer power spectra. This generalizes the Kaiser formula for monopole, quadrupole and hexadecapole of the power spectrum to all (ℓ,m) modes generated to the second order in perturbation theory. This formalism can find applications in constraining the super-sample covariance and in the local power spectrum based bispectrum estimators. As an example application, we forecast the ability to measure these modes a survey with BOSS-like galaxy number densities.

The observation of GW170817 in both gravitational and electromagnetic waves provides a number of unique tests of general relativity. One question we can answer with this event is: do large-wavelength gravitational waves and short-frequency photons experience the same number of spacetime dimensions? In models that include additional non-compact spacetime dimensions, as the gravitational waves propagate, they “leak” into the extra dimensions, leading to a reduction in the amplitude of the observed gravitational waves, and a commensurate systematic error in the inferred distance to the gravitational wave source. Electromagnetic waves would remain unaffected. We compare the inferred distance to GW170817 from the observation of gravitational waves, d_L^GW, with the inferred distance to the electromagnetic counterpart NGC 4993, d_L^EM. We constrain d_L^GW = (d_L^EM/Mpc)^γ with γ = 1.01^+0.04_−0.05 (for the SHoES value of H₀) or γ = 0.99^+0.03_−0.05 (for the Planck value of H₀), where all values are MAP and minimal 68% credible intervals. These constraints imply that gravitational waves propagate in D=3+1 spacetime dimensions, as expected in general relativity. In particular, we find that D = 4.02^+0.07_−0.10 (SHoES) and D = 3.98^+0.07_−0.09 (Planck). Furthermore, we place limits on the screening scale for theories with D>4 spacetime dimensions, finding that the screening scale must be greater than ∼ 20 Mpc. We also place a lower limit on the lifetime of the graviton of t > 4.50 × 10⁸ yr.

The atmospheric neutrino passing fraction, or self-veto, is defined as the probability for an atmospheric neutrino not to be accompanied by a detectable muon from the same cosmic-ray air shower. Building upon previous work, we propose a redefinition of the passing fractions by unifying the treatment for muon and electron neutrinos. Several approximations have also been removed. This enables performing detailed estimations of the uncertainties in the passing fractions from several inputs: muon losses, cosmic-ray spectrum, hadronic-interaction models and atmosphere-density profiles. We also study the passing fractions under variations of the detector configuration: depth, surrounding medium and muon veto trigger probability. The calculation exhibits excellent agreement with passing fractions obtained from Monte Carlo simulations. Finally, we provide a general software framework to implement this veto technique for all large-scale neutrino observatories.

We investigate the detection prospects for gravitational lensing of three-dimensional maps from upcoming line intensity surveys, focusing in particular on the impact of gravitational nonlinearities on standard quadratic lensing estimators. Using perturbation theory, we show that these nonlinearities can provide a significant contaminant to lensing reconstruction, even for observations at reionization-era redshifts. However, we show how this contamination can be mitigated with the use of a “bias-hardened” estimator. Along the way, we present an estimator for reconstructing long-wavelength density modes, in the spirit of the “tidal reconstruction” technique that has been proposed elsewhere, and discuss the dominant biases on this estimator. After applying bias-hardening, we find that a detection of the lensing potential power spectrum will still be challenging for the first phase of SKA-Low, CHIME, and HIRAX, with gravitational nonlinearities decreasing the signal to noise by a factor of a few compared to forecasts that ignore these effects. On the other hand, cross-correlations between lensing and galaxy clustering or cosmic shear from a large photometric survey look promising, provided that systematics can be sufficiently controlled. We reach similar conclusions for a single-dish survey inspired by CII measurements planned for CCAT-prime, suggesting that lensing is an interesting science target not just for 21cm surveys, but also for intensity maps of other lines.

The photon zero-mass hypothesis has been investigated for a long time using the frequency-dependent time delays of radio emissions from astrophysical sources. However, the search for a rest mass of the photon has been hindered by the similarity between the frequency-dependent dispersions due to the plasma and nonzero photon mass effects. Considering the contributions to the observed dispersion measure from both the plasma and nonzero photon mass effects, and assuming the dispersion induced by the plasma effect is an unknown constant, we obtain a robust limit on the photon mass by directly fitting a combination of the dispersion measures of radio sources. Using the observed dispersion measures from two statistical samples of extragalactic pulsars, here we show that at the 68% confidence level, the constraints on the photon mass can be as low as m_γ⩽1.51×10⁻⁴⁸ kg≃8.47×10⁻¹³ eV/c² for the sample of 22 radio pulsars in the Large Magellanic Cloud and m_γ⩽1.58×10⁻⁴⁸ kg≃8.86×10⁻¹³ eV/c² for the other sample of 5 radio pulsars in the Small Magellanic Cloud, which are comparable with that obtained by a single extragalactic pulsar. Furthermore, the statistical approach presented here can also be used when more fast radio bursts with known redshifts are detected in the future.

Axion-like particles lead to a plethora of new phenomena relating to compact astrophysical objects including stellar and black hole superradiance, axion stars and axion clusters. In this work, we investigate a new scenario in which macroscopic axion configurations are sourced by the electromagnetic fields of pulsars via the axion-photon coupling. We solve the inhomogeneous axion field equation with an explicit source term given by the electromagnetic fields of the pulsar in a rotating magnetic dipole approximation. We find that the axion profile either forms a localised boundstate or radiates as outgoing waves, depending on whether the pulsar frequency is smaller or greater than the axion mass, respectively. We derive the total mass of the scalar cloud generated around the pulsar, and the power loss for radiative solutions. We point out that it will be necessary to incorporate pulsar magnetosphere effects and their partial screening of the axion-photon interaction for a more accurate quantitative prediction. Finally, we suggest some observational signatures which should be investigated in future work.

The large scale structure (LSS) of the universe is generated by the linear density gaussian modes, which are evolved into the observed nonlinear LSS. Given a set of data the posterior surface of the modes is convex in the linear regime, leading to a unique global maximum (MAP), but this is no longer guaranteed in the nonlinear regime. In this paper we investigate the nature of posterior surface using the recently developed MAP reconstruction method, with a simplified but realistic N-body simulation as the forward model. The reconstruction method uses optimization with analytic gradients from back-propagation through the simulation. For low noise cases we recover the initial conditions well into the nonlinear regime (k∼ 1 h/Mpc) nearly perfectly. We show that the large scale modes can be recovered more precisely than the linear expectation, which we argue is a consequence of nonlinear mode coupling. For noise levels achievable with current and planned LSS surveys the reconstruction cannot recover very small scales due to noise. We see some evidence of non-convexity, specially for smaller scales where the non-injective nature of the mappings: several very different initial conditions leading to the same near perfect final data reconstruction. We investigate the nature of these phenomena further using a 1-d toy gravity model, where many well separated local maximas are found to have identical data likelihood but differ in the prior. We also show that in 1-d the prior favors some solutions over the true solution, though no clear evidence of these in 3-d. Our main conclusion is that on very small scales and for a very low noise the posterior surface is multi-modal and the global maximum may be unreachable with standard methods, while for realistic noise levels in the context of the current and next generation LSS surveys MAP optimization method is likely to be nearly optimal.

Diffuse TeV emission has been observed by H.E.S.S. in the Galactic Center region, in addition to the GeV gamma rays observed by Fermi. We propose that a population of unresolved millisecond pulsars located around the Galactic Center, suggested as possible candidates for the diffuse Galactic Center excess observed by Fermi, accelerate cosmic rays up to very high energies, and are thus also responsible for the TeV excess. We model analytically the diffusion of these accelerated protons and their interaction with the molecular clouds, producing gamma rays. The spatial and spectral dependences of the gamma rays produced can reproduce the H.E.S.S. observations, for a population of ∼ 10⁴–10⁵ millisecond pulsars above the cosmic-ray luminosity 10³⁴ erg s⁻¹, with moderate acceleration efficiency. More precise measurements at the highest energies would allow us to constrain the properties of the pulsar population, such as the magnetic field or initial spin distributions.

Halometry—mapping out the spectrum, location, and kinematics of nonluminous structures inside the Galactic halo—can be realized via variable weak gravitational lensing of the apparent motions of stars and other luminous background sources. Modern astrometric surveys provide unprecedented positional precision along with a leap in the number of cataloged objects. Astrometry thus offers a new and sensitive probe of collapsed dark matter structures over a wide mass range, from one millionth to several million solar masses. It opens up a window into the spectrum of primordial curvature fluctuations with comoving wavenumbers between 5 Mpc^-1 and 10⁵ Mpc^-1, scales hitherto poorly constrained. We outline detection strategies based on three classes of observables—multi-blips, templates, and correlations—that take advantage of correlated effects in the motion of many background light sources that are produced through time-domain gravitational lensing. While existing techniques based on single-source observables such as outliers and mono-blips are best suited for point-like lens targets, our methods offer parametric improvements for extended lens targets such as dark matter subhalos. Multi-blip lensing events may also unveil the existence, location, and mass of planets in the outer reaches of the Solar System, where they would likely have escaped detection by direct imaging.

We study the back-reaction of gravitational waves in early universe cosmology, focusing both on super-Hubble and sub-Hubble modes. Sub-Hubble modes lead to an effective energy density which scales as radiation. Hence, the relative contribution of such gravitational waves to the total energy density is constrained by big bang nucleosynthesis. This leads to an upper bound on the tensor spectral slope n_T which also depends on the tensor to scalar ratio r. Super-Hubble modes, on the other hand, lead to a negative contribution to the effective energy density, and to an equation of state of curvature. Demanding that the early universe is not dominated by the back-reaction leads to constraints on the gravitational wave spectral parameters which are derived.

Motivated by the fact that the origin of tiny Dirac neutrino masses via the standard model Higgs field and non-thermal dark matter populating the Universe via freeze-in mechanism require tiny dimensionless couplings of similar order of magnitudes (∼ 10⁻¹²), we propose a framework that can dynamically generate such couplings in a unified manner. Adopting a flavour symmetric approach based on A₄ group, we construct a model where Dirac neutrino coupling to the standard model Higgs and dark matter coupling to its mother particle occur at dimension six level involving the same flavon fields, thereby generating the effective Yukawa coupling of same order of magnitudes. The mother particle for dark matter, a complex scalar singlet, gets thermally produced in the early Universe through Higgs portal couplings followed by its thermal freeze-out and then decay into the dark matter candidates giving rise to the freeze-in dark matter scenario. Some parts of the Higgs portal couplings of the mother particle can also be excluded by collider constraints on invisible decay rate of the standard model like Higgs boson. We show that the correct neutrino oscillation data can be successfully produced in the model which predicts normal hierarchical neutrino mass. The model also predicts the atmospheric angle to be in the lower octant if the Dirac CP phase lies close to the presently preferred maximal value.

As a generalization of our previous work [Phys. Rev.D 95 (2017) 043528], in which an analytic model for the galaxy bispectrum in redshift space was developed on the basis of the halo approach, we here investigate its higher multipoles that have not been known so far. The redshift-space bispectrum includes the two variables ω and ϕ for the line-of-sight direction, and the higher multipole bispectra are defined by the coefficients in the expansion of the redshift-space bispectrum using the spherical harmonics. We find 6 new nonvanishing components out of 25 total components up to ℓ=4, in addition to 3 components discussed in the previous work (monopole, quadruple, and hexadecapole of m=0). The characteristic behaviors of the new nonvanishing multipoles are compared with the results of galaxy mock catalogs that match the halo occupation distribution of the Sloan Digital Sky Survey Baryonic Oscillation Spectroscopic Survey low-redshift sample. We find that the multipoles with m≠ 0 are also sensitive to redshift-space distortion (RSD) as well as those with m=0 and thus are key ingredients in the RSD analysis using the galaxy bispectrum. Analytic approximation formulas for these nonzero components are also presented; these are useful for understanding the characteristic behaviors.

The standard cosmographic approach consists in performing a series expansion of a cosmological observable around z=0 and then using the data to constrain the cosmographic (or kinematic) parameters at present time. Such a procedure works well if applied to redshift ranges inside the z-series convergence radius (z<1), but can be problematic if we want to cover redshift intervals that fall outside the z−series convergence radius. This problem can be circumvented if we work with the y−redshift, y=z/(1+z), or the scale factor, a=1/(1+z)=1−y, for example. In this paper, we use the scale factor a as the variable of expansion. We expand the luminosity distance and the Hubble parameter around an arbitrary ã and use the Supernovae Ia (SNe Ia) and the Hubble parameter data to estimate H, q, j and s at z≠0 (ã≠1). We show that the last relevant term for both expansions is the third. Since the third order expansion of d_L(z) has one parameter less than the third order expansion of H(z), we also consider, for completeness, a fourth order expansion of d_L(z). For the third order expansions, the results obtained from both SNe Ia and H(z) data are incompatible with the ΛCDM model at 2σ confidence level, but also incompatible with each other. When the fourth order expansion of d_L(z) is taken into account, the results obtained from SNe Ia data are compatible with the ΛCDM model at 2σ confidence level, but still remains incompatible with results obtained from H(z) data. These conflicting results may indicate a tension between the current SNe Ia and H(z) data sets.

An alternative approach to the calculation of tunneling actions, that control the exponential suppression of the decay of metastable phases, is presented. The new method circumvents the use of bounces in Euclidean space by introducing an auxiliary function, a tunneling potential V_t that connects smoothly the metastable and stable phases of the field potential V. The tunneling action is obtained as the integral in field space of an action density that is a simple function of V_t and V. This compact expression can be considered as a generalization of the thin-wall action to arbitrary potentials and allows a fast numerical evaluation with a precision below the percent level for typical potentials. The method can also be used to generate potentials with analytic tunneling solutions.

We construct a model of natural inflation in the context of α-attractor supergravity, in which both the dilaton field and the axion field are light during inflation, and the inflaton may be a combination of the two. The T-model version of this theory is defined on the Poincaré disk with radius |Z| = 1. It describes a Mexican hat potential with the flat axion direction corresponding to a circle of radius |Z| < 1. The axion decay constant f_a in this theory can be exponentially large because of the hyperbolic geometry of the Poincaré disk. Depending on initial conditions, this model may describe α-attractor inflation driven by the radial component of the inflaton field, natural inflation driven by the axion field, or a sequence of these two regimes. We also construct the E-model version of this theory, which have similar properties. In addition, we describe generalized α-attractor models where the potential can be singular at the boundary of the moduli space, and show that they can provide a simple solution for the problem of initial conditions for the models with plateau potentials.

Self tuning is one of the few methods for dynamically cancelling a large cosmological constant and yet giving an accelerating universe. Its drawback is that it tends to screen all sources of energy density, including matter. We develop a model that tempers the self tuning so the dynamical scalar field still cancels an arbitrary cosmological constant, including the vacuum energy through any high energy phase transitions, without affecting the matter fields. The scalar-tensor gravitational action is simple, related to cubic Horndeski gravity, with a nonlinear derivative interaction plus a tadpole term. Applying shift symmetry and using the property of degeneracy of the field equations we find families of functions that admit de Sitter solutions with expansion rates that are independent of the magnitude of the cosmological constant and preserve radiation and matter dominated phases. That is, the method can deliver a standard cosmic history including current acceleration, despite the presence of a Planck scale cosmological constant.

The nature of dark matter remains one of the key science questions. Weakly Interacting Massive Particles (WIMPs) are among the best motivated particle physics candidates, allowing to explain the measured dark matter density by employing standard big-bang thermodynamics. Examples include the lightest supersymmetric particle, though many alternative particles have been suggested as a solution to the dark matter puzzle. We introduce here a radically new version of the widely used DarkSUSY package, which allows to compute the properties of such dark matter particles numerically. With DarkSUSY 6 one can accurately predict a large variety of astrophysical signals from dark matter, such as direct detection rates in low-background counting experiments and indirect detection signals through antiprotons, antideuterons, gamma rays and positrons from the Galactic halo, or high-energy neutrinos from the center of the Earth or of the Sun. For thermally produced dark matter like WIMPs, high-precision tools are provided for the computation of the relic density in the Universe today, as well as for the size of the smallest dark matter protohalos. Furthermore, the code allows to calculate dark matter self-interaction rates, which may affect the distribution of dark matter at small cosmological scales. Compared to earlier versions, DarkSUSY 6 introduces many significant physics improvements and extensions. The most fundamental new feature of this release, however, is that the code has been completely re-organized and brought into a highly modular and flexible shape. Switching between different pre-implemented dark matter candidates has thus become straight-forward, just as adding new—WIMP or non-WIMP—particle models or replacing any given functionality in a fully user-specified way. In this article, we describe the physics behind the computer package, along with the main structure and philosophy of this major revision of DarkSUSY. A detailed manual is provided together with the public release at www.darksusy.org.

Primordial black holes as dark matter may be generated in single-field models of inflation thanks to the enhancement at small scales of the comoving curvature perturbation. This mechanism requires leaving the slow-roll phase to enter a non-attractor phase during which the inflaton travels across a plateau and its velocity drops down exponentially. We argue that quantum diffusion has a significant impact on the primordial black hole mass fraction making the classical standard prediction not trustable.

We extend the public CPPTRANSPORT code to calculate the statistical properties of fluctuations in multiple-field inflationary models with curved field space. Our implementation accounts for all physical effects at tree-level in the `in-in' diagrammatic expansion. This includes particle production due to time-varying masses, but excludes scenarios where the curvature perturbation is generated by averaging over the decay of more than one particle. We test our implementation by comparing results in Cartesian and polar field-space coordinates, showing excellent numerical agreement and only minor degradation in compute time. We compare our results with the PYTRANSPORT 2.0 code, which uses the same computational approach but a different numerical implementation, finding good agreement. Finally, we use our tools to study a class of gelaton-like models which could produce an enhanced non-Gaussian signal on equilateral configurations of the Fourier bispectrum. We show this is difficult to achieve using hyperbolic field-space manifolds and simple inflationary potentials.

Intrinsic alignments (IA), correlations between the intrinsic shapes and orientations of galaxies on the sky, are both a significant systematic in weak lensing and a probe of the effect of large-scale structure on galactic structure and angular momentum. In the era of precision cosmology, it is thus especially important to model IA with high accuracy. Efforts to use cosmological perturbation theory to model the dependence of IA on the large-scale structure have thus far been relatively successful; however, extant models do not consistently account for time evolution. In particular, advection of galaxies due to peculiar velocities alters the impact of IA, because galaxy positions when observed are generally different from their positions at the epoch when IA is believed to be set. In this work, we evolve the galaxy IA from the time of galaxy formation to the time at which they are observed, including the effects of this advection, and show how this process naturally leads to a dependence of IA on the velocity shear. We calculate the galaxy-galaxy-IA bispectrum to tree level (in the linear matter density) in terms of the evolved IA coefficients. We then discuss the implications for weak lensing systematics as well as for studies of galaxy formation and evolution. We find that considering advection introduces nonlocality into the bispectrum, and that the degree of nonlocality represents the memory of a galaxy's path from the time of its formation to the time of observation. We discuss how this result can be used to constrain the redshift at which IA is determined and provide Fisher estimation for the relevant measurements using the example of SDSS-BOSS.

Predictions of the next-to-leading order, i.e. one-loop, halo power spectra, depend on local and non-local bias parameters up to cubic order. The linear bias parameter can be estimated from the large scale limit of the halo-matter power spectrum, and the second order bias parameters from the large scale, tree-level bispectrum. Cubic operators would naturally be quantified using the tree-level trispectrum. As the latter is computationally expensive, we extend the quadratic field method proposed in Schmittfull et al. 2014 to cubic fields, in order to estimate cubic bias parameters. We cross-correlate a basis set of cubic bias operators with the halo field and express the result in terms of the cross-spectra of these operators, in order to cancel cosmic variance. We obtain significant detections of local and non-local cubic bias parameters, which are partially in tension with predictions based on local Lagrangian bias schemes. We directly measure the Lagrangian bias parameters of the protohaloes associated with our halo sample and clearly detect a non-local quadratic term in Lagrangian space. We do not find a clear detection of non-local cubic Lagrangian terms for low mass bins, but there is some mild evidence for their presence for the highest mass bin. While the method presented here focuses on cubic bias parameters, the approach could also be applied to quantifications of cubic primordial non-Gaussianity.

The theoretical interpretation of dark matter direct detection experiments is hindered by uncertainties of the microphysics governing the dark matter-nucleon interaction, and of the dark matter density and velocity distribution inside the Solar System. These uncertainties are especially relevant when confronting a detection claim to the null results from other experiments, since seemingly conflicting experimental results may be reconciled when relaxing the assumptions about the form of the interaction and/or the velocity distribution. We present in this paper a halo-independent method to calculate the maximum number of events in a direct detection experiment given a set of null search results, allowing for the first time the scattering to be mediated by an arbitrary combination of various interactions (concretely we consider up to 64). We illustrate this method to examine the compatibility of the dark matter interpretation of the three events detected by the silicon detectors in the CDMS-II experiment with the null results from XENON1T and PICO-60.

We investigate the strong field lensing observables for the Damour-Soludukhin wormhole and examine how small the values of the deviation parameter λ need be for reproducing the observables for the Schwarzschild black hole. While the extremely tiny values of λ indicated by the matter accretion or Hawking evaporation are quite consistent with the lensing observations, it turns out that λ could actually assume values considerably higher values and still reproduce black hole lensing signatures. The lensing observables for SgrA* can be interpreted to provide an upper bound on λ ∼ 10⁻³ and until lower bound is established, all values of λ below the upper bound should be treated as equally probable.

We investigate in detail the implications of the constant-roll condition on the inflationary era of a scalar field coupled to a teleparallel f(T) gravity. The resulting cosmological equations constitute a reconstruction technique which enables us to find either the f(T) gravity which corresponds to a given cosmological evolution, or the Hubble rate of the cosmological evolution generated by a fixed f(T) gravity. We also analyze in some detail the phase space of the constant-roll teleparallel gravity and we discuss the physical significance of the resulting fixed points and trajectories. Also we calculate the observational indices of a theory with given f(T) gravity, and we discuss all the implications of the constant-roll condition on these. As we demonstrate, the resulting theory can be compatible with the current observational data, for a wide range of values of the free parameters of the theory.

A flux of extra-terrestrial neutrinos at energies ≫10¹⁵ eV has the potential to serve as a cosmological probe of the high-energy universe as well as tests of fundamental particle interactions. Cosmogenic neutrinos, produced from the interactions of ultra-high energy cosmic rays (UHECRs) with cosmic photon backgrounds, have been regarded as a guaranteed flux. However, the expected neutrino flux depends on the composition of UHECRs at the highest energies; heavier nuclei result in lower neutrino fluxes compared to lighter nuclei and protons. The objective of this study is to estimate the range of cosmogenic neutrino spectra consistent with recent cosmic-ray spectral and compositional data using a fully inferential Bayesian approach. The study assumes a range of source distributions consistent with astrophysical sources, the flux and composition of cosmic rays, and detector systematic uncertainties. The technique applied to this study is the use of an affine-invariant Markov Chain Monte Carlo, which is an effective Bayesian inference tool for characterizing multi-dimensional parameter spaces and their correlations.

Constraints on models of the late time acceleration of the universe assume the cosmological principle of homogeneity and isotropy on large scales. However, small scale inhomogeneities can alter observational and dynamical relations, affecting the inferred cosmological parameters. For precision constraints on the properties of dark energy, it is important to assess the potential systematic effects arising from these inhomogeneities. In this study, we use the Type Ia supernova magnitude-redshift relation to constrain the inhomogeneities as described by the Dyer-Roeder distance relation and the effect they have on the dark energy equation of state (w), together with priors derived from the most recent results of the measurements of the power spectrum of the Cosmic Microwave Background and Baryon Acoustic Oscillations. We find that the parameter describing the inhomogeneities (η) is weakly correlated with w. The best fit values w = −0.933 ± 0.065 and η = 0.61 ± 0.37 are consistent with homogeneity at < 2 σ level. Assuming homogeneity (η =1), we find w = −0.961 ± 0.055, indicating only a small change in w. For a time-dependent dark energy equation of state, w₀ = −0.951 ± 0.112 and w_a = 0.059 ± 0.418, to be compared with w₀ = −0.983 ± 0.127 and w_a = 0.07 ± 0.432 in the homogeneous case, which is also a very small change. We do not obtain constraints on the fraction of dark matter in compact objects, f_p, at the 95% C.L. with conservative corrections to the distance formalism. Future supernova surveys will improve the constraints on η, and hence, f_p, by a factor of ∼10.

We consider the inflationary universe with a spectator scalar field coupled to a U(1) gauge field and calculate curvature perturbation and gravitational waves (GWs). We find that the sourced GWs can be larger than the one from vacuum fluctuation and they are statistically anisotropic as well as linearly polarized. The GW power spectrum acquires higher multipole moments with respect to the angle θ between a wave number k and a background vector field as 𝒫_h∝ (1−cos^2θ+cos^4θ−cos^6θ) irrespective of the model parameters.

We investigate static, spherically symmetric solutions in gravitational theories which have limited curvature invariants, aiming to remove the singularity in the Schwarzschild space-time. We find that if we only limit the Gauss-Bonnet term and the Ricci scalar, then the singularity at the origin persists. Moreover we find that the position corresponding to the event horizon in the original Schwarzschild space-time can develop a curvature singularity, which we call thunderbolt singularity. We also investigate a new class of theories in which all components of the Riemann tensor are bounded. We find that the thunderbolt singularity is avoidable in this theory. However, other kinds of singularities due to the dynamics of additional degrees of freedom cannot be removed, and the space-time remains singular.

Ideas borrowed from renormalization group are applied to warm inflation to characterize the inflationary epoch in terms of flows away from the de Sitter regime. In this framework different models of inflation fall into universality classes. Furthermore, for warm inflation this approach also helps to characterise when inflation can smoothly end into the radiation dominated regime. Warm inflation has a second functional dependence compared to cold inflation due to dissipation, yet despite this feature, it is shown that the universality classes defined for cold inflation can be consistently extended to warm inflation.

We perform a combined likelihood analysis for the IceCube 6-year high-energy starting events (HESE) above 60 TeV and 8-year throughgoing muon events above 10 TeV using a two-component neutrino flux model. The two-component flux can be motivated either from purely astrophysical sources or due to a beyond Standard Model contribution, such as decaying heavy dark matter. As for the astrophysical neutrinos, we consider two different source flavor compositions corresponding to the standard pion decay and muon-damped pion decay sources. We find that the latter is slightly preferred over the former as the high-energy component, while the low-energy component does not show any such preference. We also take into account the multi-messenger gamma-ray constraints and find that our two-component fit is compatible with these constraints, whereas the single-component power-law bestfit to the HESE data is ruled out. The astrophysical plus dark matter interpretation of the two-component flux is found to be mildly preferred by the current data and the gamma-ray constraints over the purely astrophysical explanation.

Universe history in R²-gravity is studied from “beginning" up to the present epoch. It is assumed that initially the curvature scalar R was sufficiently large to induce the proper duration of inflation. Gravitational particle production by the oscillating R(t) led to a graceful exit from inflation, but the cosmological evolution in the early universe was drastically different from the standard one till the universe age reached the value of the order of the inverse decay rate of the oscillating curvature R(t). This deviation from the standard cosmology might have a noticeable impact on the formation of primordial black holes and baryogenesis. At later time, after exponential decay of the curvature oscillations, cosmology may return to normality.

The observed power spectrum in redshift space appears distorted due to the peculiar motion of galaxies, known as redshift-space distortions (RSD). While all the effects in RSD are accounted for by the simple mapping formula from real to redshift spaces, accurately modeling redshift-space power spectrum is rather difficult due to the non-perturbative properties of the mapping. Still, however, a perturbative treatment may be applied to the power spectrum at large-scales, and on top of a careful modeling of the Finger-of-God effect caused by the small-scale random motion, the redshift-space power spectrum can be expressed as a series of expansion which contains the higher-order correlations of density and velocity fields. In our previous work [JCAP 8 (Aug., 2016) 050], we provide a perturbation-theory inspired model for power spectrum in which the higher-order correlations are evaluated directly from the cosmological N-body simulations. Adopting a simple Gaussian ansatz for Finger-of-God effect, the model is shown to quantitatively describe the simulation results. Here, we further push this approach, and present an accurate power spectrum template which can be used to estimate the growth of structure as a key to probe gravity on cosmological scales. Based on the simulations, we first calibrate the uncertainties and systematics in the pertrubation theory calculation in a fiducial cosmological model. Then, using the scaling relations, the calibrated power spectrum template is applied to a different cosmological model. We demonstrate that with our new template, the best-fitted growth functions are shown to reproduce the fiducial values in a good accuracy of 1% at k<0.18 Mpc^-1 for cosmologies with different Hubble parameters.

We investigate the ratios of critical physical quantities related to the T−S criticality of charged AdS black holes. It is shown that the ratio T_cSc/Q_c is universal while T_crc/Q_c is not. This finding is quite interesting considering the former observation that both the T−S graph and T−r₊ graph exhibit reverse van der Waals behavior. It is also worth noting that the value of T_cSc/Q_c differs from that of P_cvc/T_c for P−V criticality. Moreover, we discuss ratios for the P−V criticality and Q−Φ criticality. By introducing the dimensional analysis technique, we successfully interpret the phenomenon that the ratio Φ_cQc/T_c is not universal and construct two universal ratios for the Q−Φ criticality instead. It is expected that the dimensional analysis technique can be generalized to probe the universal ratios for Y−X criticality in future research.

The DAMA/LIBRA collaboration has recently released updated results from their search for the annual modulation signal expected from Dark Matter (DM) scattering in their NaI detectors. We have fitted the updated DAMA result for the modulation amplitudes in terms of a Weakly Interacting Massive Particle (WIMP) signal, parameterizing the interaction with nuclei in terms of the most general effective Lagrangian for a WIMP particle spin up to 1/2, systematically assuming dominance of one of the 14 possible interaction terms, and assuming for the WIMP velocity distribution a standard Maxwellian. We find that most of the couplings of the non-relativistic effective Hamiltonian can provide a better fit compared to the standard Spin Independent interaction case, and with a reduced fine-tuning of the three parameters (WIMP mass, WIMP-nucleon effective cross-section and ratio between the WIMP-neutron and the WIMP-proton couplings). Moreover, effective models for which the cross section depends explicitly on the WIMP incoming velocity can provide a better fit of the DAMA data at large values of m_χ compared to the standard velocity-independent cross-section due to a different phase of the modulation amplitudes. All the best fit solutions are in tension with exclusion plots of both XENON1T and PICO60.

We study, for the first time, the shadow of the supermassive black hole Sgr A^* at the center of the Milky Way in dark matter halos. For the Cold Dark Matter and Scalar Field Dark Matter models considered in this work, the apparent shapes of the shadow depend upon the black hole spin a and the dark matter parameter k. We find that both dark matter models influence the shadow in a similar way. The shadow is a perfect circle in the non-rotating case (a=0) and a deformed one in the rotating case (a≠0). The size of the shadow increases with increasing k in both non-rotating and rotating cases, while the shadow gets more and more distorted with increasing a in the rotating case. We further investigate the black hole emission rate in both dark matter halos. We find that the emission rate decreases with increasing k and the peak of the emission shifts to lower frequency. Finally, by calculating the angular radius of the shadow, we estimate that the dark matter halo could influence the shadow of Sgr A^* at a level of order of magnitude of 10⁻³ μas and 10⁻⁵ μas, for CDM and SFDM, respectively. Future astronomical instruments with high angular resolution would be able to observe this effect and shed light on the nature of Sgr A^*. More interestingly, it may be possible to distinguish between CDM and SFDM models given the resolutions required differing by two orders of magnitude from each other.

The rich vacuum structure of multi-Higgs extensions of the Standard Model (SM) may have interesting cosmological implications for the electroweak phase transition (EWPT). As an important example of such class of models, we consider a particularly simple low-energy SM-like limit of a recently proposed Grand-Unified Trinification model with the scalar sector composed of two Higgs doublets and a complex singlet and with a global U(1) family symmetry. The fermion sector of this model is extended with a family of vector-like quarks which enhances CP violation. With the current study, we aim at exploring the generic vacuum structure and uncovering the features of the EWPT in this model relevant for cosmology. We show the existence of different phase transition patterns providing strong departure from thermal equilibrium. Most of these observations are not specific to the considered model and may generically be expected in other multi-Higgs extensions of the SM.

Cosmological simulations of the ΛCDM model suggest that the dark matter halos of dwarf galaxies are denser in their center than what observational data of such galaxies imply. In this letter, we propose a novel solution to this problem by invoking a certain class of dark matter self-heating processes. As we will argue, such processes lead to the formation of dark matter cores at late times by considerably reducing the inner mass density of dwarf-sized halos. For deriving concrete results, we focus on semi-annihilating dark matter scenarios and model the inner region of dark matter halos as a gravothermal fluid. An important aspect of this new solution is that the semi-annihilation effects are much more prominent in dwarf-sized halos than in the more massive halos that host galaxies and clusters, even if the corresponding cross sections are the same. Furthermore, the preferred parameter space for solving the small-scale problem suggests a thermal dark matter candidate with a mass below the GeV scale, which can be probed in dark matter direct and indirect detection experiments.

We present the consistent theory of a free massive spin-2 field with 5 degrees of freedom propagating in spacetimes with an arbitrary geometry. We obtain this theory via linearizing the equations of the ghost-free massive gravity expressed in the tetrad formalism. The theory is parameterized by a non-symmetric rank-2 tensor whose 16 components fulfill 11 constraints implied by the equations. When restricted to Einstein spaces, the theory reproduces the standard description of massive gravitons. In generic spacetimes, the theory does not show the massless limit and always propagates five degrees of freedom, even for the vanishing mass parameter. We illustrate these features by an explicit calculation for a homogeneous and isotropic cosmological background. It turns out that the spin-2 particles are always stable if they are sufficiently massive, hence they may be a part of the Dark Mater.

We make a comparison for thirteen dark energy (DE) models by using current cosmological observations, including type Ia supernova, baryon acoustic oscillations, and cosmic microwave background. To perform a systematic and comprehensive analysis, we consider three statistics methods of SNIa, including magnitude statistic (MS), flux statistic (FS), and improved flux statistic (IFS), as well as two kinds of BAO data. In addition, Akaike information criteria (AIC) and Bayesian information criteria (BIC) are used to assess the worth of each model. We find that: (1) The thirteen models can be divided into four grades by performing cosmology-fits. The cosmological constant model, which is most favored by current observations, belongs to grade one; αDE, constant w and generalized Chaplygin gas models belong to grade two; Chevalliear-Polarski-Linder (CPL) parametrization, Wang parametrization, doubly coupled massive gravity, new generalized Chaplygin gas and holographic DE models belong to grade three; agegraphic DE, Dvali-Gabadadze-Porrati, Vacuum metamorphosis and Ricci DE models, which are excluded by current observations, belong to grade four. (2) For parameter estimation, adopting IFS yields the biggest Ω_m and the smallest h for all the models. In contrast, using different BAO data does not cause significant effects. (3) IFS has the strongest constraint ability on various DE models. For examples, adopting IFS yields the smallest value of ΔAIC for all the models; in addition, making use of this technique yields the biggest figure of merit for CPL and Wang parametrizations.

A novel fractal analysis of the cosmic web structure is carried out, employing the Sloan Digital Sky Survey, data release 7. We consider the large-scale stellar mass distribution, unlike other analyses, and determine its multifractal geometry, which is compared with the geometry of the cosmic web generated by cosmological N-body simulations. We find a good concordance, the common features being: (i) a minimum singularity strength α_min = 1, which corresponds to the edge of diverging gravitational energy and differs from the adhesion model prediction; (ii) a “supercluster set” of relatively high dimension where the mass concentrates; and (iii) a non-lacunar structure, like the one generated by the adhesion model.

As dark matter (DM) direct detection experiments continue to improve their sensitivity they will inevitably encounter an irreducible background arising from coherent neutrino scattering. This so-called “neutrino floor” may significantly reduce the sensitivity of an experiment to DM-nuclei interactions, particularly if the recoil spectrum of the neutrino background is approximately degenerate with the DM signal. This occurs for the conventionally considered spin-independent (SI) or spin-dependent (SD) interactions. In such case, an increase in the experiment's exposure by multiple orders of magnitude may not yield any significant increase in sensitivity. The typically considered SI and SD interactions, however, do not adequately reflect the whole landscape of the well-motivated DM models, which includes other interactions. Since particle DM has not been detected yet in laboratories, it is essential to understand and maximize the detection capabilities for a broad variety of possible models and signatures. In this work we explore the impact of the background arising from various neutrino sources on the discovery potential of a DM signal for a large class of viable DM-nucleus interactions and several potential futuristic experimental settings, with different target elements. For some momentum suppressed cross sections, large DM particle masses and heavier targets, we find that there is no suppression of the discovery limits due to neutrino backgrounds. Further, we explicitly demonstrate that inelastic scattering, which could appear in models with multicomponent dark sectors, would help to lift the signal degeneracy associated with the neutrino floor. This study could assist with mapping out the optimal DM detection strategy for the next generation of experiments.

The absence of confirmed signal in dark matter (DM) direct detection (DD) may suggest weak interaction strengths between DM and the abundant constituents inside nucleon, i.e. gluons and valence light quarks. In this work we consider a real scalar dark matter S interacting only with SU(2)_L singlet Up-type quarks U_i = u_R,c_R,t_R via a vector-like fermion ψ which has the same quantum number as U_i. The DM-nucleon scattering can proceed through both h-mediated Higgs portal (HP) and ψ-mediated vector-like portal (VLP), in which HP can receive sizable radiative corrections through the new fermions. We first study the separate constraints on the new Yukawa couplings y_i and find that the constraints of XENON1T results are strong on y₁ from VLP scattering and on y₃ from its radiative contributions to HP scattering. Since both DM-light quark interactions and HP have been well studied in the existing literature, we move forward to focus on DM-heavy quark interactions. Since there is no valence c,t quark inside nucleons at μ_had ∼ 1 GeV, y₂,y₃ interactions are manifested in DM-gluon scattering at loop level. We find that renormalization group equation (RGE) and heavy quark threshold effects are important if one calculates the DM-nucleon scattering rate σ^SI_p at μ_had ∼ 1 GeV while constructing the effective theory at μ_EFT ∼ m_Z. For the benchmarks y₃ = 0.5, y₂ = 0.5, 1, 3, combined results from Ω_DM h² ≃ 0.12, XENON1T, Fermi-LAT, 13 TeV LHC data have almost excluded m_S < m_t/2 when only DM-{c,t} interactions are considered. FCNC of top quark can be generated at both tree level t → ψ^(*)S → cSS and loop level t → c+γ/g/Z, of which the branching fractions are typically below 10⁻⁹ after passing the other constraints, which are still safe from the current top quark width measurements.

The next generation of space-borne gravitational wave detectors may detect gravitational waves from extreme mass-ratio inspirals with primordial black holes. To produce primordial black holes which contribute a non-negligible abundance of dark matter and are consistent with the observations, a large enhancement in the primordial curvature power spectrum is needed. For a single field slow-roll inflation, the enhancement requires a very flat potential for the inflaton, and this will increase the number of e-folds. To avoid the problem, an ultra-slow-roll inflation at the near inflection point is required. We elaborate the conditions to successfully produce primordial black hole dark matter from single field inflation and propose a toy model with polynomial potential to realize the big enhancement of the curvature power spectrum at small scales while maintaining the consistency with the observations at large scales. The power spectrum for the second order gravitational waves generated by the large density perturbations at small scales is consistent with the current pulsar timing array observations.

Understanding the isotopic composition of cosmic rays (CRs) observed near Earth represents a milestone towards the identification of their origin. Local fluxes contain all the known stable and long-lived isotopes, reflecting the complex history of primaries and secondaries as they traverse the interstellar medium. For that reason, a numerical code which aims at describing the CR transport in the Galaxy must unavoidably rely on accurate modelling of the production of secondary particles. In this work we provide a detailed description of the nuclear cross sections and decay network as implemented in the forthcoming release of the galactic propagation code DRAGON2. We present the secondary production models implemented in the code and we apply the different prescriptions to compute quantities of interest to interpret local CR fluxes (e.g., nuclear fragmentation timescales, secondary and tertiary source terms). In particular, we develop a nuclear secondary production model aimed at accurately computing the light secondary fluxes (namely: Li, Be, B) above 1 GeV/n. This result is achieved by fitting existing empirical or semi-empirical formalisms to a large sample of measurements in the energy range 100 MeV/n to 100 GeV/n and by considering the contribution of the most relevant decaying isotopes up to iron. Concerning secondary antiparticles (positrons and antiprotons), we describe a collection of models taken from the literature, and provide a detailed quantitative comparison.

We consider mechanisms for producing a significant population of primordial black holes (PBHs) within string inspired single field models of inflation. The production of PBHs requires a large amplification in the power spectrum of curvature perturbations between scales associated with CMB and PBH formation. In principle, this can be achieved by temporarily breaking the slow-roll conditions during inflation. In this work, we identify two string setups that can realise this process. In string axion models of inflation, subleading non-perturbative effects can superimpose steep cliffs and gentle plateaus onto the leading axion potential. The cliffs can momentarily violate the slow-roll conditions, and the plateaus can lead to phases of ultra slow-roll inflation. We thus achieve a string motivated model which both matches the Planck observations at CMB scales and produces a population of light PBHs, which can account for an order one fraction of dark matter. In DBI models of inflation, a sharp increase in the speed of sound sourced by a steep downward step in the warp factor can drive the amplification. In this scenario, discovery of PBHs could indicate non-trivial dynamics in the bulk, such as flux-antibrane annihilation at the tip of a warped throat.

We examine scenarios in which a dark sector (dark matter, dark radiation, or dark energy) couples to the active neutrinos. For light and weakly-coupled exotic sectors we find that scalar, vector, or tensor dark backgrounds may appreciably impact neutrino propagation while remaining practically invisible to all other phenomenological probes. The dark medium may induce small departures from the Standard Model predictions or even offer an alternative explanation of neutrino oscillations. While the propagation of neutrinos is affected in all experiments, atmospheric data currently represent the most promising probe of the new physics scale. We quantify the future sensitivity of the ORCA detector of KM3NeT and the IceCube experiment and find that all exotic effects can be constrained at the level of a few percent of the Earth matter potential, with couplings mediating μ-neutrino transitions being most constrained. Long baseline experiments like DUNE may provide additional complementary information on the scale of the dark sector.

We derive constraints on mixed dark-matter scenarios consisting of primordial black holes (PBHs) and weakly interacting massive particles (WIMPs). In these scenarios, we expect a density spike of the WIMPs that are gravitationally bound to the PBHs, which results in an enhanced annihilation rate and increased indirect detection prospects. We show that such scenarios provide strong constraints on the allowed fraction of PBHs that constitutes the dark matter, depending on the WIMP mass m_χ and the velocity-averaged annihilation cross-section ⟨σv⟩. For the standard scenario with m_χ = 100 GeV and ⟨σv⟩ = 3 × 10⁻²⁶ cm³/s, we derive bounds that are stronger than all existing bounds for PBHs with masses 10⁻¹² M_⊙ ≲ M_BH ≲ 10⁴ M_⊙, where M_⊙ is the solar mass, and mostly so by several orders of magnitude.

When combining data sets to perform parameter inference, the results will be unreliable if there are unknown systematics in data or models. Here we introduce a flexible methodology, BACCUS: BAyesian Conservative Constraints and Unknown Systematics, which deals in a conservative way with the problem of data combination, for any degree of tension between experiments. We introduce parameters that describe a bias in each model parameter for each class of experiments. A conservative posterior for the model parameters is then obtained by marginalization both over these unknown shifts and over the width of their prior. We contrast this approach with an existing method in which each individual likelihood is scaled, comparing the performance of each approach and their combination in application to some idealized models. Using only these rescaling is not a suitable approach for the current observational situation, in which internal null tests of the errors are passed, and yet different experiments prefer models that are in poor agreement. The possible existence of large shift systematics cannot be constrained with a small number of data sets, leading to extended tails on the conservative posterior distributions. We illustrate our method with the case of the H₀ tension between results from the cosmic distance ladder and physical measurements that rely on the standard cosmological model.

In the axion monodromy inflation, the inflation is driven by the axion with super-Planckian field values in a monomial potential with superimposed sinusoidal modulations. The coupling of the axion to massless gauge fields can induce copious particle production during inflation, resulting in large non-Gaussian curvature perturbation that leads to the formation of primordial black holes. In this paper, we explore the parameter space in the axion monodromy inflation model that favors the formation of primordial black holes with masses ranging from 10⁸ grams to 20 solar masses. We also study the associated gravitational waves and their detection in pulsar timing arrays and interferometry experiments.