We study the production of fermions through a derivative coupling with a pseudoscalar inflaton and the effects of the produced fermions on the scalar primordial perturbations. We present analytic results for the modification of the scalar power spectrum due to the produced fermions, and we estimate the amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we find a regime where the effect of the fermions gives the dominant contribution to the scalar spectrum while the amplitude of the bispectrum is small and in agreement with observation. We also note the existence of a regime in which the backreaction of the fermions on the evolution of the zero-mode of the inflaton can lead to inflation even if the potential of the inflaton is steep and does not satisfy the slow-roll conditions.

The recent measurement of the Higgs boson mass implies a relatively slow rise of the standard model Higgs potential at large scales, and a possible second minimum at even larger scales. Consequently, the Higgs field may develop a large vacuum expectation value during inflation. The relaxation of the Higgs field from its large postinflationary value to the minimum of the effective potential represents an important stage in the evolution of the Universe. During this epoch, the time-dependent Higgs condensate can create an effective chemical potential for the lepton number, leading to a generation of the lepton asymmetry in the presence of some large right-handed Majorana neutrino masses. The electroweak sphalerons redistribute this asymmetry between leptons and baryons. This Higgs relaxation leptogenesis can explain the observed matter-antimatter asymmetry of the Universe even if the standard model is valid up to the scale of inflation, and any new physics is suppressed by that high scale.PACS numbers: 98.80. Cq, 11.30.Fs, 14.80.Bn The recent discovery of a Higgs boson with mass 125 GeV [1,2] implies that the Higgs potential is very shallow and may even develop a second minimum, assuming that the standard model is valid at high energy scales [3]. During cosmological inflation, the Higgs field may be trapped in a quasistable second minimum or, alternatively, may develop a stochastic distribution of vacuum expectation values due to the flatness of the potential [4][5][6]. In both scenarios, the Higgs field relaxes to its vacuum state after inflation via a coherent motion. In this Letter we explore this epoch of Higgs relaxation.We show that the observed matter-antimatter asymmetry could arise during this epoch. The Sakharov conditions [7], necessary for baryogenesis, are generically satisfied in the presence of the out-of-equilibrium Higgs condensate evolving with time [8,9] and the neutrino Majorana masses that violate the lepton number.The standard model Higgs boson has a tree-level po-where Φ is an SU(2) doublet. Using a gauge transformation, one can write the classical field as Φ = 1/ √ 2){e iθ φ, 0 , where φ(x) is real. Loop corrections substantially modify this potential at large values. We will include one-loop and finite temperature corrections to the Higgs potential, although twoloop effects may also be important near the metastability boundary [3]. For the experimentally preferred top and Higgs mass values, the φ 2 = v EW = 246 GeV minimum appears to be metastable [3], which entails a number of important ramifications [10]. However, a stable vacuum is still possible within the experimental uncertainties [3]. Furthermore, higher-dimensional operators can modify the potential at large vacuum expectation value (VEV) [? ] and make the vacuum stable. During inflation, a scalar field may develop a nonzero VEV φ 2 for more than one reason. We will consider two cosmological scenarios that lead to two types of initial conditions.Initial condition 1 (IC-1).-IC-1 occurs for the central values of measured Higgs an...

Dark matter (DM) with sizeable self-interactions mediated by a light species offers a compelling explanation of the observed galactic substructure; furthermore, the direct coupling between DM and a light particle contributes to the DM annihilation in the early universe. If the DM abundance is due to a dark particle-antiparticle asymmetry, the DM annihilation cross-section can be arbitrarily large, and the coupling of DM to the light species can be significant. We consider the case of asymmetric DM interacting via a light (but not necessarily massless) Abelian gauge vector boson, a dark photon. In the massless dark photon limit, gauge invariance mandates that DM be multicomponent, consisting of positive and negative dark ions of different species which partially bind in neutral dark atoms. We argue that a similar conclusion holds for light dark photons; in particular, we establish that the multi-component and atomic character of DM persists in much of the parameter space where the dark photon is sufficiently light to mediate sizeable DM self-interactions. We discuss the cosmological sequence of events in this scenario, including the dark asymmetry generation, the freeze-out of annihilations, the dark recombination and the phase transition which gives mass to the dark photon. We estimate the effect of self-interactions in DM haloes, taking into account this cosmological history. We place constraints based on the observed ellipticity of large haloes, and identify the regimes where DM self-scattering can affect the dynamics of smaller haloes, bringing theory in better agreement with observations. Moreover, we estimate the cosmological abundance of dark photons in various regimes, and derive pertinent bounds.1 Since the primary incentive for considering asymmetric DM is not any theoretical expectation of new physics related to the electroweak interactions of the SM, invoking dark interactions and dark light species is a completely natural possibility which does not remove any of the motivation for this class of theories. 2 If asymmetric DM carries non-Abelian gauge charges, gauge-charge neutrality can often be ensured also by an appropriate combination of the various "flavours" or "colours" of the DM multiplet(s). Referring again to ordinary matter, the valence quarks of protons and neutrons form SU(3)c-neutral combinations.

An epoch of Higgs relaxation may occur in the early universe during or immediately following postinflationary reheating. It has recently been pointed out that leptogenesis may occur in minimal extensions of the Standard Model during this epoch [1]. We analyse Higgs relaxation taking into account the effects of perturbative and non-perturbative decays of the Higgs condensate, and we present a detailed derivation of the relevant kinetic equations and of the relevant particle interaction cross sections. We identify the parameter space in which a sufficiently large asymmetry is generated.

During inflation, scalar fields, including the Higgs boson, may acquire a nonzero vacuum expectation value, which must later relax to the equilibrium value during reheating. In the presence of the time-dependent condensate, the vacuum state can evolve into a state with a nonzero particle number. We show that, in the presence of lepton number violation in the neutrino sector, the particle production can explain the observed matter-antimatter asymmetry of the universe. We find that this form of leptogenesis is particularly effective when the Higgs condensate decays rapidly and at low reheat scale. As part of the calculation, we present some exact results for the Bogoliubov transformations for Majorana fermions with a nonzero time-dependent chemical potential, in addition to a time-dependent mass.