The observation of gravitational waves from a binary neutron star merger by LIGO/VIRGO and the associated electromagnetic counterpart provides a high precision test of orbital dynamics, and therefore a new and sensitive probe of extra forces and new radiative degrees of freedom. Axions are one particularly well-motivated class of extensions to the Standard Model leading to new forces and sources of radiation, which we focus on in this paper. Using an effective field theory (EFT) approach, we calculate the first post-Newtonian corrections to the orbital dynamics, radiated power, and gravitational waveform for binary neutron star mergers in the presence of an axion. This result is applicable to many theories which add an extra massive scalar degree of freedom to General Relativity. We then perform a detailed forecast of the potential for Advanced LIGO to constrain the free parameters of the EFT, and map these to the mass ma and decay constant fa of the axion. At design sensitivity, we find that Advanced LIGO can potentially exclude axions with ma 10 −11 eV and fa ∼ (10 14 − 10 17 ) GeV. There are a variety of complementary observational probes over this region of parameter space, including the orbital decay of binary pulsars, black hole superradiance, and laboratory searches. We comment on the synergies between these various observables.

Observations of gravitational radiation from compact binary systems provide an unprecedented opportunity to test General Relativity in the strong field dynamical regime. In this paper, we investigate how future observations of gravitational radiation from binary neutron star mergers might provide constraints on finite-range forces from a universally coupled massive scalar field. Such scalar degrees of freedom are a characteristic feature of many extensions of General Relativity. For concreteness, we work in the context of metric f (R) gravity, which is equivalent to General Relativity and a universally coupled scalar field with a non-linear potential whose form is fixed by the choice of f (R). In theories where neutron stars (or other compact objects) obtain a significant scalar charge, the resulting attractive finite-range scalar force has implications for both the inspiral and merger phases of binary systems. We first present an analysis of the inspiral dynamics in Newtonian limit, and forecast the constraints on the mass of the scalar and charge of the compact objects for the Advanced LIGO gravitational wave observatory. We then perform a comparative study of binary neutron star mergers in General Relativity with those of a one-parameter model of f (R) gravity using fully relativistic hydrodynamical simulations. These simulations elucidate the effects of the scalar on the merger and post-merger dynamics. We comment on the utility of the full waveform (inspiral, merger, post-merger) to probe different regions of parameter space for both the particular model of f (R) gravity studied here and for finite-range scalar forces more generally.

We probe the self-interactions of dark matter with relaxed galaxy groups and clusters using observational data from strong and weak lensing and stellar kinematics. Our analysis uses the Jeans formalism and considers a wider range of systematic effects than in previous work, including adiabatic contraction and stellar anisotropy, to robustly constrain the self-interaction cross section. For both groups and clusters, our results show a mild preference for a nonzero cross section compared with cold collisionless dark matter. Our groups result, σ/m = 0.5 ± 0.2 cm 2 /g, places the first constraint on self-interacting dark matter (SIDM) at an intermediate scale M 200 ∼ 10 14 M between galaxies and massive clusters. For massive clusters with M 200 ∼ 10 15 M , our result is σ/m = 0.19 ± 0.09 cm 2 /g, with an upper limit of σ/m < 0.35 cm 2 /g (95% CL). Thus, our results disfavor a velocity-independent cross section of order 1 cm 2 /g or larger needed to impact small scale structure problems in galaxies, but are consistent with a velocity-dependent cross section that decreases with increasing scattering velocity. Comparing the cross sections with and without the effect of adiabatic contraction, we find that adiabatic contraction produces slightly larger values for our data sample, but they are consistent at the 1σ level. Finally, to validate our approach, we apply our Jeans analysis to a sample of mock data generated from SIDM-plus-baryons simulations with σ/m = 1 cm 2 /g. This is the first test of the Jeans model at the level of stellar and lensing observables directly measured from simulations. We find our analysis gives a robust determination of the cross section, as well as consistently inferring the true baryon and dark matter density profiles.

The Lyman-α forest is a valuable probe of dark matter models featuring a scale-dependent suppression of the power spectrum as compared to ΛCDM. In this work, we present a new estimator of the Lyman-α flux power spectrum that does not rely on hydrodynamical simulations. Our framework is characterized by nuisance parameters that encapsulate the complex physics of the intergalactic medium and sensitivity to highly non-linear small-scale modes. After validating the approach based on high-resolution hydrodynamical simulations for ΛCDM, we derive conservative constraints on interacting dark matter models from BOSS Lyman-α data on large scales, k < 0.02 (km/s) −1 , with the relevant nuisance parameters left free in the model fit. The estimator yields lower bounds on the mass of cannibal dark matter, where freeze-out occurs through 3 → 2 annihilation, in the MeV range. Furthermore, we find that models of dark matter interacting with dark radiation, which have been argued to address the H 0 and σ 8 tensions, are compatible with BOSS Lyman-α data.

We study soft limits of correlation functions for the density and velocity fields in the theory of structure formation. First, we re-derive the (resummed) consistency conditions at unequal times using the eikonal approximation. These are solely based on symmetry arguments and are therefore universal. Then, we explore the existence of equal-time relations in the soft limit which, on the other hand, depend on the interplay between soft and hard modes. We scrutinize two approaches in the literature: The time-flow formalism, and a background method where the soft mode is absorbed into a locally curved cosmology. The latter has been recently used to set up (angular averaged) 'equal-time consistency relations'. We explicitly demonstrate that the timeflow relations and 'equal-time consistency conditions' are only fulfilled at the linear level, and fail at next-to-leading order for an Einstein de-Sitter universe. While applied to the velocities both proposals break down beyond leading order, we find that the 'equal-time consistency conditions' quantitatively approximates the perturbative results for the density contrast. Thus, we generalize the background method to properly incorporate the effect of curvature in the density and velocity fluctuations on short scales, and discuss the reasons behind this discrepancy. We conclude with a few comments on practical implementations and future directions. IntroductionSoft limits, that link (n + 1)-point and n-point correlators of the density perturbations in the theory of structure formation, have recently received significant attention. The main appeal of these relations (for unequal times) is that they are solely based on the assumption of a singlefield inflationary background, providing the seed for the initial conditions, together with the diffeomorphism invariance of General Relativity. Therefore, they lead to (quite generally) nonperturbative statements about the system on short scales that serve as a probe of basic aspects of the theory at hand [1][2][3][4][5][6][7][8][9]. This becomes a very powerful tool in the context of using the forthcoming large-scale structure (LSS) surveys to test single-field inflation as a theory of initial conditions for the seed of structure, as well as the equivalence principle in gravitational theories, especially since fluctuations enter the non-linear regime at small redshift.Various approaches have been used to derive soft limits for correlation functions in LSS. 1 As stated, these relations are most meaningful for correlation functions at different times. For equal-time correlators they become degenerate, in the sense that they vanish at leading order in q, with q being the soft (or long) mode. 2 To extract information about equal-time correlators, one therefore has to study next-to-leading order (NLO) effects, where dynamical information, as opposite to gauge artifacts in General Relativity, start to become important [2,3,15]. It is then relevant to determine whether at equal times one may be able to write down expressions that are still...

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We present an effective model for the one-dimensional Lyman-α flux power spectrum far above the baryonic Jeans scale. The main new ingredient is constituted by a set of two parameters that encode the impact of small, highly non-linear scales on the one-dimensional power spectrum on large scales, where it is measured by BOSS. We show that, by marginalizing over the model parameters that capture the impact of the intergalactic medium, the flux power spectrum from both simulations and observations can be described with high precision. The model displays a degeneracy between the neutrino masses and the (unknown, in our formalism) normalization of the flux power spectrum. This degeneracy can be lifted by calibrating one of the model parameters with simulation data, and using input from Planck CMB data. We demonstrate that this approach can be used to extract bounds on the sum of neutrino masses with comparably low numerical effort, while allowing for a conservative treatment of uncertainties from the dynamics of the intergalactic medium. An explorative analysis yields an upper bound of 0.16eV at 95% C.L. when applied to BOSS data at 3 ≤ z ≤ 4.2. We also forecast that if the systematic and statistical errors will be reduced by a factor two the upper bound will become 0.1eV at 95% C.L, and 0.056eV when assuming a 1% error.

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