Search

We revisit alternative mechanisms of gravitational wave production during inflation and argue that they generically emit a non-negligible amount of scalar fluctuations. We find the scalar power is larger than the tensor power by a factor of order 1/ε². For an appreciable tensor contribution, the associated scalar emission completely dominates the zero-point fluctuations of the inflaton, resulting in a tensor-to-scalar ratio r~ε². A more quantitative result can be obtained if one further assumes that gravitational waves are emitted by localized subhorizon processes, giving rmax≃0.3ε². However, ε is generally time dependent, and this result for r depends on its instantaneous value during the production of the sources, rather than just its average value, somewhat relaxing constraints from the tilt ns. We calculate the scalar 3-point correlation function in the same class of models and show that non-Gaussianity cannot be made arbitrarily small, i.e. fNL≳1, independently of the value of r. Possible exceptions in multifield scenarios are discussed. [ABSTRACT FROM AUTHOR]

We further develop the description of redshift-space distortions within the effective field theory of large scale structures. First, we generalize the counterterms to include the effect of baryonic physics and primordial non-Gaussianity. Second, we evaluate the IR resummation of the dark matter power spectrum in redshift space. This requires us to identify a controlled approximation that makes the numerical evaluation straightforward and efficient. Third, we compare the predictions of the theory at one loop with the power spectrum from numerical simulations up to ℓ=6. We find that the IR resummation allows us to correctly reproduce the baryon acoustic oscillation peak. The k reach-or, equivalently, the precision for a given k-depends on additional counterterms that need to be matched to simulations. Since the nonlinear scale for the velocity is expected to be longer than the one for the overdensity, we consider a minimal and a nonminimal set of counterterms. The quality of our numerical data makes it hard to firmly establish the performance of the theory at high wave numbers. Within this limitation, we find that the theory at redshift z=0.56 and up to ℓ=2 matches the data at the percent level approximately up to k∼0.13 hMpc-1 or k∼0.18 hMpc-1, depending on the number of counterterms used, with a potentially large improvement over former analytical techniques. [ABSTRACT FROM AUTHOR]

We assess two potential signals of the formation of our universe by the decay of a false vacuum. Negative spatial curvature is one possibility, but the window for its detection is now small. However, another possible signal is a suppression of the cosmic microwave background (CMB) power spectrum at large angles. This arises from the steepening of the effective potential as it interpolates between a flat inflationary plateau and the high barrier separating us from our parent vacuum. We demonstrate that these two effects can be parametrically separated in angular scale. Observationally, the steepening effect appears to be excluded at large ℓ; but it remains consistent with the slight lack of power below ℓ ≈ 30 found by the WMAP and Planck collaborations. We give two simple models which improve the fit to the Planck data; one with observable curvature and one without. Despite cosmic variance, we argue that future CMB polarization and most importantly large-scale structure observations should be able to corroborate the Planck anomaly if it is real. If we further assume the specific theoretical setting of a landscape of metastable vacua, as suggested by string theory, we can estimate the probability of seeing a low-ℓ suppression in the CMB. There are significant theoretical uncertainties in such calculations, but we argue the probability for a detectable suppression may be as large as O(1), and in general is significantly larger than the probability of seeing curvature. [ABSTRACT FROM AUTHOR]

An accurate theoretical template for the galaxy power spectrum is key for the success of ongoing and future spectroscopic surveys. We examine to what extent the effective field theory (EFT) of large-scale structure is able to provide such a template and correctly estimate cosmological parameters. To that end, we initiate a blinded challenge to infer cosmological parameters from the redshift-space power spectrum of high-resolution mock catalogs mimicking the BOSS galaxy sample but covering a 100 times larger cumulative volume. This gigantic simulation volume allows us to separate systematic bias due to theoretical modeling from the statistical error due to sample variance. The challenge is to measure three unknown input parameters used in the simulation: the Hubble constant, the matter density fraction, and the clustering amplitude. We present analyses done by two independent teams, who have fitted the mock simulation data generated by yet another independent group. This allows us to avoid any confirmation bias by analyzers and to pin down possible tuning of the specific EFT implementations. Both independent teams have recovered the true values of the input parameters within subpercent statistical errors corresponding to the total simulation volume. [ABSTRACT FROM AUTHOR]

Gravitational-wave observations of coalescing binary systems allow for novel tests of the strong-field regime of gravity. Using data from the Gravitational Wave Open Science Center (GWOSC) of the LIGO and Virgo detectors, we place the first constraints on an effective-field-theory based extension of general relativity, in which only higher-order curvature terms are added to the Einstein-Hilbert action. We construct gravitational-wave templates describing the quasicircular, adiabatic inspiral phase of binary black holes in this extended theory of gravity. Then, after explaining how to properly take into account the region of validity of the effective field theory when performing tests of general relativity, we perform Bayesian model selection using the two lowest-mass binary-black-hole events reported to date by LIGO and Virgo--GW151226 and GW170608--and constrain this theory with respect to general relativity. We find that these data disfavor the appearance of new physics on distance scales around ~150 km. Finally, we describe a general strategy for improving constraints as more observations will become available with future detectors on the ground and in space. [ABSTRACT FROM AUTHOR]