Ogan Özsoy, Gizem Sengor, Kuver Sinha, Scott Watson

In this note we propose a model independent framework for inflationary (p)reheating. Our approach is analogous to the Effective Field Theory of Inflation, however here the inflaton oscillations provide an additional source of (discrete) symmetry breaking. Using the Goldstone field that non-linearly realizes time diffeormorphism invariance we construct a model independent action for both the inflaton and reheating sectors. Utilizing the hierarchy of scales present during the reheating process we are able to recover known results in the literature in a simpler fashion, including the presence of oscillations in the primordial power spectrum. We also construct a class of models where the shift symmetry of the inflaton is preserved during reheating, which helps alleviate past criticisms of (p)reheating in models of Natural Inflation. Extensions of our framework suggest the possibility of analytically investigating non-linear effects (such as rescattering and back-reaction) during thermalization without resorting to lattice methods. By construction, the EFT relates the strength of many of these interactions to other operators in the theory, including those responsible for the efficiency of (p)reheating. We conclude with a discussion of the limitations and challenges for our approach.

Eleonora Di Valentino, Alessandro Melchiorri, Joseph Silk

Cosmological constraints are usually derived under the assumption of a $6$ parameters $\Lambda$-CDM theoretical framework or simple one-parameter extensions. In this paper we present, for the first time, cosmological constraints in a significantly extended scenario, varying up to $12$ cosmological parameters simultaneously, including the sum of neutrino masses, the neutrino effective number, the dark energy equation of state, the gravitational waves background and the running of the spectral index of primordial perturbations. Using the latest Planck 2015 data release (with polarization) we found no significant indication for extensions to the standard $\Lambda$-CDM scenario, with the notable exception of the angular power spectrum lensing amplitude, $A_{\rm lens}$ that is larger than the expected value at more than two standard deviations even when combining the Planck data with BAO and supernovae type Ia external datasets. In our extended cosmological framework, we find that a combined Planck+BAO analysis constrains the value of the r.m.s. density fluctuation parameter to $\sigma_8=0.781_{-0.063}^{+0.065}$ at $95 \%$ c.l., helping to relieve the possible tensions with the CFHTlenS cosmic shear survey. We also find a lower value for the reionization optical depth $\tau=0.058_{-0.043}^{+0.040}$ at $95$ \% c.l. respect to the one derived under the assumption of $\Lambda$-CDM. The scalar spectral index $n_S$ is now compatible with a Harrison-Zeldovich spectrum to within $2.5$ standard deviations. Combining the Planck dataset with the HST prior on the Hubble constant provides a value for the equation of state $w < -1$ at more than two standard deviations while the neutrino effective number is fully compatible with the expectations of the standard three neutrino framework.

E. Babichev, C. Charmousis, D. Langlois, R. Saito

We show that the two additional Lagrangians that appear in theories beyond Horndeski can be reexpressed in terms of simple generalizations of the "John" and "Paul" terms of the Fab Four theories. We find that these extended Fab Four satisfy the same properties of self-tuning as the original Fab Four.

Gary Prezeau

It is shown that compact bodies project out strands of concentrated dark matter filaments henceforth simply called hairs. These hairs are a consequence of the fine-grained stream structure of dark matter halos, and as such constitute a new physical prediction of $\Lambda$CDM. Using both an analytical model of planetary density and numerical simulations utilizing the {\it Fast Accurate Integrand Renormalization } (FAIR) algorithm (a fast geodesics calculator described below) with realistic planetary density inputs, dark matter streams moving through a compact body are shown to produce hugely magnified dark matter densities along the stream velocity axis going through the center of the body. Typical hair density enhancements are $10^7$ for Earth and $10^8$ for Jupiter. The largest enhancements occur for particles streaming through the core of the body that mostly focus at a single point called the root of the hair. For the Earth, the root is located at about $10^6$~km from the planetary center with a density enhancement of around $10^9$ while for a gas giant like Jupiter, the root is located at around $10^{5}$~km with a enhancement of around $10^{11}$.

Clare Burrage, Edmund J. Copeland

We review the tantalising prospect that the first evidence for the dark energy driving the observed acceleration of the Universe on giga-parsec scales may be found through metre scale laboratory based atom interferometry experiments. To do that, we first introduce the idea that scalar fields could be responsible for dark energy and show that in order to be compatible with fifth force constraints these fields must have a screening mechanism which hides their effects from us within the solar system. Particular emphasis is placed on one such screening mechanism known as the chameleon effect where the field's mass becomes dependent on the environment. The way the field behaves in the presence of a spherical source is determined and we then go on to show how in the presence of the kind of high vacuum associated with atom interferometry experiments, and when the test particle is an atom, it is possible to use the associated interference pattern to place constraints on the acceleration due to the fifth force of the chameleon field - this has already been used to rule out large regions of the chameleon parameter space and maybe one day will be able to detect the force due to the dark energy field in the laboratory.

P. Ivanov, S. V. Chernov

(abbreviated) We study quantized solutions of WdW equation describing a closed FRW universe with a $\Lambda $ term and a set of massless scalar fields. We show that when $\Lambda \ll 1$ in the natural units and the standard $in$-vacuum state is considered, either wavefunction of the universe, $\Psi$, or its derivative with respect to the scale factor, $a$, behave as random quasi-classical fields at sufficiently large values of $a$, when $1 \ll a \ll e^{{2\over 3\Lambda}}$ or $a \gg e^{{2\over 3\Lambda}}$, respectively. Statistical r.m.s value of the wavefunction is proportional to the Hartle-Hawking wavefunction for a closed universe with a $\Lambda $ term. Alternatively, the behaviour of our system at large values of $a$ can be described in terms of a density matrix corresponding to a mixed state, which is directly determined by statistical properties of $\Psi$. It gives a non-trivial probability distribution over field velocities. We suppose that a similar behaviour of $\Psi$ can be found in all models exhibiting copious production of excitations with respect to $out$-vacuum state associated with classical trajectories at large values of $a$. Thus, the third quantization procedure may provide a 'boundary condition' for classical solutions of WdW equation.

Tommaso Giannantonio, Eiichiro Komatsu

Bayesian model comparison penalizes models with more free parameters that are allowed to vary over a wide range, and thus offers the most robust method to decide whether some given data require new parameters. In this paper, we ask a simple question: do current cosmological data require extensions of the simplest single-field inflation models? Specifically, we calculate the Bayesian evidence of a totally anti-correlated isocurvature perturbation and a running spectral index of the scalar curvature perturbation. These parameters are motivated by recent claims that the observed temperature anisotropy of the cosmic microwave background on large angular scales is too low to be compatible with the simplest inflation models. Both a subdominant, anti-correlated cold dark matter isocurvature component and a negative running index succeed in lowering the large-scale temperature power spectrum. We show that the introduction of isocurvature perturbations is disfavored, whereas that of the running spectral index is only moderately favored, even when the BICEP2 data are included in the analysis without any foreground subtraction.

Pedro Ruiz-Femenia, Mehran Zahiri-Abyaneh

A method to find relations between the operators in the mesonic Lagrangian of Chiral Perturbation Theory at order p^6 is presented. The procedure can be used to establish if the basis of operators in the Lagrangian is minimal. As an example, we apply the method to the two-flavour case in the absence of scalar and pseudo-scalar sources (s=p=0), and conclude that the minimal Lagrangian contains 27 independent operators.

Mehrdad Mirbabayi, Marko Simonović

Various inflationary scenarios can often be distinguished from one another by looking at the squeezed limit behavior of correlation functions. Therefore, it is useful to have a framework designed to study this limit in a more systematic and efficient way. We propose using an expansion in terms of weakly coupled super-horizon degrees of freedom, which is argued to generically exist in a near de Sitter space-time. The modes have a simple factorized form which leads to factorization of the squeezed-limit correlation functions with power-law behavior in $k_{\rm long}/k_{\rm short}$. This approach reproduces the known results in single-, quasi-single-, and multi-field inflationary models. However, it is applicable even if, unlike the above examples, the additional degrees of freedom are not weakly coupled at sub-horizon scales. Stronger results are derived in two-field (or sufficiently symmetric multi-field) inflationary models. We discuss the observability of the non-Gaussian 3-point function in the large-scale structure surveys, and argue that the squeezed limit behavior has a higher detectability chance than equilateral behavior when it scales as $(k_{\rm long}/k_{\rm short})^\Delta$ with $\Delta<1$ -- where local non-Gaussianity corresponds to $\Delta=0$.