Daniel G. Figueroa

Decay of the standard model Higgs field after inflation

This work is supported by the Research Project of the Spanish MINECO No. FPA2012-39684-C03-02 and the Centro de Excelencia Severo Ochoa Program No. SEV-2012-0249. F. T. is supported by the FPI-Severo Ochoa Ph.D. Fellowship No. SVP-2013-067697

Curvaton decay by resonant production of the Standard Model higgs

We investigate in detail a model where the curvaton is coupled to the Standard Model higgs. Parametric resonance might be expected to cause a fast decay of the curvaton, so that it would not have time to build up the curvature perturbation. However, we show that this is not the case, and that the resonant decay of the curvaton may be delayed even down to electroweak symmetry breaking. This delay is due to the coupling of the higgs to the thermal background, which is formed by the Standard Model degrees of freedom created from the inflaton decay. We establish the occurrence of the delay by considering the curvaton evolution and the structure of the higgs resonances. We then provide analytical expressions for the delay time, and for the subsequent resonant production of the higgs, which ultimately leads to the curvaton effective decay width. Contrary to expectations, it is possible to obtain the observed curvature perturbation for values of the curvaton-higgs coupling as large as 10−1. Our calculations also apply in the general case of curvaton decay into any non Standard Model species coupled to the thermal background.

Anisotropies in the Gravitational Wave Background from Preheating

We investigate the anisotropies in the gravitational wave (GW) background produced at preheating after inflation. Using lattice field theory simulations of a massless preheating model, we show that the GW amplitude depends sensitively on the value of the decay product field χ coupled to the inflaton φ, with the only requisite that χ is light during inflation. We find a strong anisotropy in the amplitude of the GW background on large angular scales, the details of which strongly depend on the reheating dynamics. We expect similar conclusions for a wide class of inflationary models with light scalar fields. If future direct detection GW experiments are capable of detecting the GW produced by preheating, they should also be able to detect this effect. This could eventually provide a powerful way to distinguish between different inflationary and preheating scenarios.

Gravitational wave production from the decay of the standard model Higgs field after inflation

This work is supported by the Research Project of the Spanish MINECO, Grant No. FPA2013-47986-03-3P, and the Centro de Excelencia Severo Ochoa Program No. SEV-2012-0249. F.T. is supported by the FPI-Severo Ochoa Ph.D. fellowship No. SVP-2013-067697. We acknowledge the use of the IFT Hydra cluster for the development of this work

On the anisotropy of the gravitational wave background from massless preheating

When a light scalar field is present during inflation, its value varies on superhorizon scales, modulating the preheating process at the end of inflation. Consequently, the amplitude of the gravitational wave (GW) background produced during preheating is also modulated. The observed energy density of this background appears therefore anisotropic at different angles in the sky. We provide a master formula for the angular power spectrum Cl of the anisotropies in the GW background from preheating, valid for any scenario where the anisotropies are due to the superhorizon modulation of a light degree of freedom. Using lattice field theory simulations of massless preheating with g2/λ = 2, we find a flat angular spectrum l(l+1)Cl ≈ 3 × 10−4, which represents a strong anisotropy of ~ 1% variations on large angular scales. For our choice of couplings, long wavelengths are amplified most strongly during parametric resonance, which is crucial for the development of the anisotropies. If future direct detection GW observatories are capable of detecting backgrounds of cosmological origin, they {may also} be able to detect this effect. This could eventually become a powerful tool to discriminate among inflationary and preheating scenarios.

Stochastic Background of Gravitational Waves from Fermions, { Theory and Applications {

A bstractOut-of-equilibrium fermions can be created in the early Universe by non-perturbative parametric effects, both at preheating or during the thermal era. An anisotropic stress is developed in the fermion distribution, acting as a source of a stochastic background of gravitational waves (GW). We derive a general formalism to calculate the spectrum of GW produced by an ensemble of fermions, which we apply to a variety of scenarios after inflation. We discuss in detail the regularization of the source, i.e. of the unequal-time-correlator of the fermions’ transverse-traceless anisotropic stress. We discuss how the GW spectrum builds up in time and present a simple parametrization of its final amplitude and peak frequency. We find that fermions may generate a GW background with a significant amplitude at very high frequencies, similarly to the case of preheating with scalar fields. A detection of this GW background would shed light on the physics of the very early Universe, but new technology at high frequencies is required, beyond the range accessible to currently planned detectors.

Can self-ordering scalar fields explain the BICEP2 B-mode signal?

We show that self-ordering scalar fields (SOSF), i.e. non-topological cosmic defects arising after a global phase transition, cannot explain the B-mode signal recently announced by BICEP2. We compute the full C{sub l}{sup B} angular power spectrum of B-modes due to vector and tensor perturbations of SOSF, modeled in the large N limit of a spontaneously broken global O(N) symmetry. We conclude that the low l multipoles detected by BICEP2 cannot be due mainly to SOSF, since they have the wrong spectrum at low multipoles. As a byproduct we derive the first cosmological constraints on this model, showing that the BICEP2 B-mode polarization data admits at most a 2-3% contribution from SOSF in the temperature anisotropies, similar to (but somewhat tighter than) the recently studied case of cosmic strings.

Stochastic Background of Gravitational Waves from Fermions

Preheating and other particle production phenomena in the early Universe can give rise to high- energy out-of-equilibrium fermions with an anisotropic stress. We develop a formalism to calculate the spectrum of gravitational waves due to fermions, and apply it to a variety of scenarios after inflation. We pay particular attention to regularization issues. We show that fermion production sources a stochastic background of gravitational waves with a significant amplitude, but we find that typical frequencies of this new background are not within the presently accessible direct detec- tion range. However, small-coupling scenarios might still produce a signal observable by planned detectors, and thus open a new window into the physics of the very early Universe.

Gravitational wave production from preheating: parameter dependence

Parametric resonance is among the most efficient phenomena generating gravitational waves (GWs) in the early Universe. The dynamics of parametric resonance, and hence of the GWs, depend exclusively on the resonance parameter q. The latter is determined by the properties of each scenario: the initial amplitude and potential curvature of the oscillating field, and its coupling to other species. Previous works have only studied the GW production for fixed value(s) of q. We present an analytical derivation of the GW amplitude dependence on q, valid for any scenario, which we confront against numerical results. By running lattice simulations in an expanding grid, we study for a wide range of q values, the production of GWs in post-inflationary preheating scenarios driven by parametric resonance. We present simple fits for the final amplitude and position of the local maxima in the GW spectrum. Our parametrization allows to predict the location and amplitude of the GW background today, for an arbitrary q. The GW signal can be rather large, as h2ΩGW(fp) 10−11, but it is always peaked at high frequencies fp 107 Hz. We also discuss the case of spectator-field scenarios, where the oscillatory field can be e.g. a curvaton, or the Standard Model Higgs.

Cosmic Microwave Background temperature and polarization anisotropies from the large-N limit of global defects

This work is supported by the Swiss National Science Foundation. Some numerical calculations were run on the Andromeda cluster of the University of Geneva. The authors also acknowledge financial support from the Madrid Regional Government (CAM) under the program HEPHACOS S2009/ESP-1473-02, from the Spanish MICINN under Grant No. AYA2009-13936-C06-06 and Consolider-Ingenio 2010 PAU (Grant No. CSD2007-00060), and from the MINECO, Centro de Excelencia Severo Ochoa Programme, under Grant No. SEV-2012-0249, as well as from the European Union Marie Curie Initial Training Network UNILHC PITN-GA-2009-237920.