The early Universe may have passed through an extended period of matter-dominated expansion following inflation and prior to the onset of radiation domination. Sub-horizon density perturbations grow gravitationally during such an epoch, collapsing into bound structures if it lasts long enough. The strong analogy between this phase and structure formation in the present-day universe allows the use of N-body simulations and approximate methods for halo formation to model the fragmentation of the inflaton condensate into inflaton halos. For a simple model we find these halos have masses of up to $20\,\mathrm{kg}$ and radii of the order of $10^{-20}\,\mathrm{m}$, roughly $10^{-24}$ seconds after the Big Bang. We find that the N-body halo mass function matches predictions of the mass-Peak Patch method and the Press-Schechter formalism within the expected range of scales. A long matter-dominated phase would imply that reheating and thermalization occurs in a universe with large variations in density, potentially modifying the dynamics of this process. In addition, large overdensities can source gravitational waves and may lead to the formation of primordial black holes.
We propose a new inflation model in which a gauge singlet inflaton turns into the Higgs condensate after inflation. The inflationary path is characterized by a moduli space of supersymmetric vacua spanned by the inflaton and Higgs field. The inflation energy scale is related to the soft supersymmetry breaking, and the Hubble parameter during inflation is smaller than the gravitino mass. The initial condition for the successful inflation is naturally realized by the pre-inflation in which the Higgs plays a role of the waterfall field.
We investigate the emergence of large, localized, pseudo-stable configurations (oscillons) from inflaton fragmentation at the end of inflation. We predict the number density of large oscillons, and the conditions necessary for their emergence in a class of inflationary models. Analytic estimates are provided for a 3+1 and 1+1-dimensional universe. We test our predictions with detailed numerical simulations in 1+1-dimensions. We see a zoo of oscillons emerging from the simulations, including the usual small amplitude "sech" oscillons as well as large "flat-topped" oscillons. The emergent oscill…
We discuss the cosmological gravitino problem in inflation models in which the inflaton potential is constructed from Kähler potential rather than superpotential: a representative model is $\overline{\text{D}3}$-induced geometric inflation. A critical ingredient in this type of models is the coupling of the inflaton and Polonyi (supersymmetry-breaking) field in the Kähler potential, which is needed to build the inflaton potential. We point out the same coupling let the inflaton dominantly decay into a pair of inflatino and gravitino causing the gravitino problem. We propose some possible solut…
We propose a possibility that the inflaton potential is significantly modified after inflation due to heavy field dynamics. During inflation there may be a heavy scalar field stabilized at a value deviated from the low-energy minimum. As the heavy field moves to the low-energy minimum, the inflaton potential could be significantly modified. In extreme cases, the inflaton potential vanishes and the inflaton becomes almost massless at some time after inflation. Such transition of the inflaton potential has interesting implications for primordial density perturbations, reheating, creation of unwa…
We study reheating in $α$-attractor models of inflation in which the inflaton couples to other scalars or fermions. We show that the parameter space contains viable regions in which the inflaton couplings to radiation can be determined from the properties of CMB temperature fluctuations, in particular the spectral index. This may be the only way to measure these fundamental microphysical parameters, which shaped the universe by setting the initial temperature of the hot big bang and contain important information about the embedding of a given model of inflation into a more fundamental theory o…
In this paper, we investigate the parameter space in the framework of hilltop supernatural inflation in which the inflaton field can play the role of Affleck-Dine field to produce successful baryogenesis. The suitable value of reheating temperature could coincide with the reheating temperature required to produce lightest supersymmetric particle dark matter. The baryon isocurvature perturbation is shown to be negligible. We consider $p=3$, $p=4$, and $p=6$ type III hilltop inflation and discuss how to connect the models to supersymmetric theories.
We study preheating after hilltop inflation where the inflaton couples to another scalar field, e.g. a right-handed sneutrino, which provides a mechanism for generating the correct initial conditions for inflation and also a decay channel for the inflaton that allows for reheating and non-thermal leptogenesis. In the presence of such a coupling, we find that after the phases of tachyonic preheating and tachyonic oscillations, during which the inflaton field becomes inhomogeneous, there can be a subsequent preheating phase where the fluctuations of the other field get resonantly enhanced, from …
The inflaton must convert its energy into radiation after inflation, which, in a conventional scenario, is caused by the perturbative inflaton decay. This reheating process would be much more complicated in some cases: the decay products obtain masses from an oscillating inflaton and thermal environment, and hence the conventional reheating scenario can be modified. We study in detail processes of particle production from the inflaton, their subsequent thermalization and evolution of inflaton/plasma system by taking dissipation of the inflaton in a hot plasma into account. It is shown that the…
We study a recently proposed running kinetic inflation model in which the inflaton potential becomes flat due to rapid growth of the kinetic term at large inflaton field values. As concrete examples, we build a variety of chaotic inflation models in supergravity with e.g. quadratic, linear, and fractional-power potentials. The power of the potential generically increases after inflation, and the inflaton is often massless at the potential minimum in the supersymmetric limit, which leads to many interesting phenomena. First, the light inflaton mass greatly relaxes severe thermal and non-thermal…
We propose a scenario to flatten inflaton potential for a small-field slow-roll inflation from the origin. In the scenario, inflaton mass-square gets through a renormalization group running which depends on not only inflaton field but also an assisting field. Thanks to the assisting field participating in the running, initial condition for a slow-roll inflation can be set naturally, and inflaton potential can be flattened by the vacuum expectation value of the field. Applying this idea, we propose a scenario of inflation, dubbed here as \textit{assisted hilltop inflation}, which is free from t…
Status of light inflaton: from inflation to laboratory
Indian Institute of Technology Guwahati（印度理工学院古瓦哈提分校）；Indian Institute of Technology Hyderabad（印度理工学院海德拉巴分校）；Indian Institute of Science Education and Research, Thiruvananthapuram（印度科学教育与研究机构（特鲁凡得琅））；SRM University-AP（SRM大学安得拉邦校区）
We propose an extension of natural inflation, where the inflaton potential is a general periodic function. Specifically, we study elliptic inflation where the inflaton potential is given by Jacobi elliptic functions, Jacobi theta functions or the Dedekind eta function, which appear in gauge and Yukawa couplings in the string theories compactified on toroidal backgrounds. We show that in the first two cases the predicted values of the spectral index and the tensor-to-scalar ratio interpolate from natural inflation to exponential inflation such as $R^2$- and Higgs inflation and brane inflation, …
We consider D-term inflation for small couplings of the inflaton to matter fields. Standard hybrid inflation then ends at a critical value of the inflaton field that exceeds the Planck mass. During the subsequent waterfall transition the inflaton continues its slow-roll motion, whereas the waterfall field rapidly grows by quantum fluctuations. Beyond the decoherence time, the waterfall field becomes classical and approaches a time-dependent minimum, which is determined by the value of the inflaton field and the self-interaction of the waterfall field. During the final stage of inflation, the e…
We consider the extension of the Standard Model (SM) with a light inflaton where both unitarity problem in Higgs inflation and vacuum instability problem are resolved. The linear non-minimal coupling of the inflaton to gravity leads to a significant kinetic mixing between the inflaton and the graviton such that perturbative unitarity is restored up to Planck scale. We show the correlation between unitarity scale and inflationary observables in this model and discuss how the effective Higgs inflation appears.
We construct a chaotic inflation model in which the Higgs fields play the role of the inflaton in the standard model as well as in the singlet extension of the supersymmetric standard model. The key idea is to allow a non-canonical kinetic term for the Higgs field. The model is a realization of the recently proposed running kinetic inflation, in which the coefficient of the kinetic term grows as the inflaton field. The inflaton potential depends on the structure of the Higgs kinetic term. For instance, the inflaton potential is proportional to phi^2 and phi^{2/3} in the standard model and NMSS…
In order for the inflaton to decay into radiation at the end of inflation, it needs to couple to light matter fields. In this article we determine whether such couplings cause the inflaton to decay during inflation rather than after it. We calculate decay amplitudes during inflation, and determine to what extent such processes have an impact on the mean and variance of the inflaton, as well as on the expected energy density of its decay products. Although the exponential growth of the decay amplitudes with the number of e-folds appears to indicate the rapid decay of the inflaton, cancellations…
A new scenario of hybrid-like inflation is considered without using hybrid-type potential. Radiation raised continuously by a dissipating inflaton field keeps symmetry restoration in a remote sector, and the false-vacuum energy of the remote sector dominates the energy density during inflation. Remote inflation is terminated when the temperature reaches the critical temperature, or when the slow-roll condition is violated. Without introducing a complex form of couplings, inflaton field may either roll-in (like a standard hybrid inflation) or roll-out (like an inverted-hybrid model or quintesse…
We discuss inflaton decays and reheating in no-scale Starobinsky-like models of inflation, calculating the effective equation-of-state parameter, $w$, during the epoch of inflaton decay, the reheating temperature, $T_{\rm reh}$, and the number of inflationary e-folds, $N_*$, comparing analytical approximations with numerical calculations. We then illustrate these results with applications to models based on no-scale supergravity and motivated by generic string compactifications, including scenarios where the inflaton is identified as an untwisted-sector matter field with direct Yukawa coupling…
In this paper, we consider a chaotic inflation model where the role of inflaton is played by the Higgs triplet in type II seesaw mechanism for generating the small masses of left-handed neutrinos. Leptogenesis could happen after inflation. This model is constructed without introducing supersymmetry (SUSY).
We revisit the scenario where inflation is preceded by a radiation era by considering that the inflaton too could have been in thermal equilibrium early in the radiation era. Hence we take into account not only the effect of a pre-inflationary era on the inflaton mode functions but also that of a frozen thermal distribution of inflaton quanta. We initially discuss in detail the issues relevant to our scenario of a pre-inflationary radiation dominated era and then obtain the scalar power spectrum for this scenario. We find that the power spectrum is free from infrared divergences. We then use t…
In the context of the Higgs model involving gauge and Yukawa interactions with the spontaneous gauge symmetry breaking, we consider $λϕ^4$ inflation with non-minimal gravitational coupling, where the Higgs field is identified as inflaton. Since the inflaton quartic coupling is very small, once quantum corrections through the gauge and Yukawa interactions are taken into account, the inflaton effective potential most likely becomes unstable. In order to avoid this problem, we need to impose stability conditions on the effective inflaton potential, which lead to not only non-trivial relations amo…
Recently, an interesting inflationary scenario, named Gauss-Bonnet inflation, is proposed by Kanti et al.~\cite{Kanti:2015pda,Kanti:2015dra}. In the model, there is no inflaton potential but the inflaton couples to the Guass-Bonnet term. In the case of quadratic coupling, they find inflation occurs with graceful exit. The scenario is attractive because of the natural set-up. However, we show there exists the gradient instability in the tensor perturbations in this inflationary model. We further prove the no-go theorem for the Gauss-Bonnet inflation without an inflaton potential.
We consider hybrid inflation for small couplings of the inflaton to matter such that the critical value of the inflaton field exceeds the Planck mass. It has recently been shown that inflation then continues at subcritical inflaton field values where quantum fluctuations generate an effective inflaton mass. The effective inflaton potential interpolates between a quadratic potential at small field values and a plateau at large field values. An analysis of the allowed parameter space leads to predictions for the scalar spectral index n_s and the tensor-to-scalar ratio r similar to those of natur…
We construct a natural inflation model in supergravity where the inflaton is identified with a modulus field possessing a shift symmetry. The superpotential for the inflaton is generated by meson condensation due to strong dynamics with deformed moduli constraints. In contrast to models based on gaugino condensation, the inflaton potential is generated without $R$-symmetry breaking and hence does not depend on the gravitino mass. Thus, our model is compatible with low scale supersymmetry.
We investigate the possibility that the primordial perturbation has two sources: the inflaton and a spectator field, which is not dynamically important during inflation but which after inflation can contribute to the curvature perturbation. The recent Planck results on the power spectrum and non-Gaussianity allow us to put constraints on such mixed models. In the generic case, where no specific model for the inflaton or the spectator is assumed, one finds that in the mixed scenario it is possible to have a large trispectrum with tau_NL >> (f_NL)^2. The constraints on inflation models in the pl…
We study preheating in DBI hybrid inflation. Preheating occurs since the matter fields are non-minimally coupled to the inflaton. Despite the coupling being small, preheating happens as a narrow parametric resonance in which matter fields and inflaton modes are exponentially created. We show that, within the approximations used, the process is very efficient at late times. The resonance stage gives way to the decay of the inflaton into bosonic or fermionic degrees of freedom and the corresponding reheating temperature is determined.
The 750 GeV resonance observed by ATLAS and CMS may be explained by a gauge singlet scalar. This would provide an ideal candidate for a gauge singlet scalar alternative to Higgs Inflation, S-inflation. Here we discuss the relevant results of S-inflation in the context of the 750 GeV resonance. In particular, we show that a singlet scalar, if it is real, has a major advantage over the Higgs boson with regard to unitarity violation during inflation. This is because it is possible to restrict the large non-minimal coupling required for inflation, $ξ\sim 10^5$, to the real singlet scalar, with all…
When models of new inflation are implemented in supergravity, the inflaton is a complex and not a real scalar field. As a complex scalar field has two independent components, supergravity models of new inflation are naturally two-field models. In this paper, we use the delta N formalism to analyse how the two-field behaviour modifies the usual single-field predictions. We find that the model reduces to the single-field limit if the inflaton mass term is sufficiently small. Otherwise, the imaginary inflaton component reduces the amplitude A_s and the spectral index n_s of the scalar curvature p…
We examine the oscillon formation in a recently proposed inflation model of the pure natural inflation, where the inflaton is an axion that couples to a strongly-coupled pure Yang-Mills theory. The plateau of the inflaton potential, which is favored by recent observations, drives the fragmentation of the inflaton and can produce spatially localized oscillons. We find that the oscillons are formed for F<~ O(0.1) M_{Pl}, with F the effective decay constant of the model. We also comment on observational implications of the oscillons.
BICEP2 measurement of primordial tensor modes in CMB suggests that cosmological inflation is due to a slowly rolling inflaton taking trans-Planckian values and provides further experimental evidence for the absence of large $M_{\rm P}$ induced operators. We show that classical scale invariance solves the problem and allows for a remarkably simple scale-free inflaton model without any gauge group. Due to trans-Planckian inflaton values and VEVs, a dynamically induced Coleman-Weinberg-type inflaton potential of the model can predict tensor-to-scalar ratio $r$ in a large range. Precise determinat…
In 'hilltop inflation', inflation takes place when the inflaton field slowly rolls from close to a maximum of its potential (i.e. the 'hilltop') towards its minimum. When the inflaton potential is associated with a phase transition, possible topological defects produced during this phase transition, such as domain walls, are efficiently diluted during inflation. It is typically assumed that they also do not reform after inflation, i.e. that the inflaton field stays on its side of the 'hill', finally performing damped oscillations around the minimum of the potential. In this paper we study the …
Slow-roll inflation requires the inflaton field to have an exceptionally flat potential, which combined with measurements of the scale of inflation demands some degree of fine-tuning. Alternatively, the flatness of the potential could be due to the inflaton's origin as a pseudo-Goldstone boson, as in Natural Inflation. Alas, consistency with Planck data places the original proposal of Natural Inflation in a tight spot, as it requires a trans-Planckian excursion of the inflaton. Although one can still tune the renormalizable potential to sub-Planckian values, higher order corrections from quant…
We propose that inflation is driven by a (complex) neutral Higgs of the MSSM extension of the SM, in a chaotic-like inflation setting. The SUSY breaking soft term masses are of order $10^{12}-10^{13}$ GeV, which is identified with the inflaton mass scale and is just enough to stabilise the SM Higgs potential. The fine-tuned SM Higgs has then a mass around 126 GeV, in agreement with LHC results. We point out that the required large field excursions of chaotic inflation may be realised in string theory with the (complex) inflaton/Higgs identified with a continuous Wilson line or D-brane position…
The recent BICEP2 measurements of B-modes indicate a large tensor-to-scalar ratio in inflationary cosmology, which points towards trans-Planckian evolution of the inflaton. We propose possible string-theory realizations thereof. Schemes for natural and axion monodromy inflation are presented in the framework of the type IIB large volume scenario. The inflaton in both cases is given by the universal axion and its potential is generated at subleading order by F-terms. Our models are shown to feature a natural mechanism for inflaton decay into predominantly Standard Model particles.
We discuss non-minimal quadratic inflation in supersymmetric (SUSY) and non-SUSY models which entails a linear coupling of the inflaton to gravity. Imposing a lower bound on the parameter cR, involved in the coupling between the inflaton and the Ricci scalar curvature, inflation can be attained even for subplanckian values of the inflaton while the corresponding effective theory respects the perturbative unitarity up to the Planck scale. Working in the non-SUSY context we also consider radiative corrections to the inflationary potential due to a possible coupling of the inflaton to bosons or f…
We show that density perturbations seeded by the inflaton can be suppressed when having additional light degrees of freedom contributing to the production of perturbations. The inflaton fluctuations affect the light field dynamics by modulating the length of the inflationary period, hence produce additional density perturbations in the post-inflationary era. Such perturbations can cancel those generated during inflation as both originate from the same inflaton fluctuations. This allows production of large gravitational waves from small-field inflation, which is normally forbidden by the Lyth b…
Using a semiclassical approach to Gravitoelectromagnetic Inflation (GEMI), we study the origin and evolution of seminal inflaton and electromagnetic fields in the early inflationary universe from a 5D vacuum state. We use simultaneously the Lorentz and Feynman gauges. Our formalism is naturally not conformal invariant on the effective 4D de Sitter metric, which make possible the super adiabatic amplification of electric and magnetic field modes during the early inflationary epoch of the universe on cosmological scales. This is the first time that solutions for the electric field fluctuations a…
If the cosmological inflationary scenario took place in the cosmic landscape in string theory, the inflaton, the scalar mode responsible for inflation, would have meandered in a complicated multi-dimensional potential. We show that this meandering property naturally leads to many e-folds of inflation, a necessary condition for a successful inflationary scenario. This behavior also leads to fluctuations in the primordial power spectrum of the cosmic microwave background radiation, which may be detected in a near future cosmic variance limited experiment like PLANCK.
We present a model where inflation and Dark Matter takes place via a single scalar field phi. Without introducing any new parameters we are able unify inflation and Dark Matter using a scalar field phi that accounts for inflation at an early epoch while it gives a Dark Matter WIMP particle at low energies. After inflation our universe must be reheated and we must have a long period of radiation dominated before the epoch of Dark Matter. Typically the inflaton decays while it oscillates around the minimum of its potential. If the inflaton decay is not complete or sufficient then the remaining e…
We propose a variant scenario of spontaneous baryogenesis from asymmetric inflaton based on current-current interactions between the inflaton and matter fields with a non-zero B-L charge. When the inflaton starts to oscillate around the minimum after inflation, it may lead to excitation of a CP-odd component, which induces an effective chemical potential for the B-L number through the current-current interactions. We study concrete inflation models and show that the spontaneous baryogenesis scenario can be naturally implemented in the chaotic inflation in supergravity.
Primordial turbulence from inflation: a new inflaton-driven turbulent regime
Nordita, KTH Royal Institute of Technology and Stockholm University（诺尔迪塔，皇家理工学院与斯德哥尔摩大学）；The Oskar Klein Centre, Stockholm University（奥斯卡·克莱因中心，斯德哥尔摩大学）；Instituut-Lorentz of Theoretical Physics, Universiteit Leiden（莱顿大学洛伦兹理论物理研究所）；McWilliams Center for Cosmology & Department of Physics, Carnegie Mellon University（卡内基梅隆大学麦克威廉姆斯宇宙学中心与物理系）；School of Natural Sciences and Medicine, Ilia State University（伊利亚州立大学自然科学与医学院）
We study particle production at the preheating era in inflation models with nonminimal coupling $ξϕ^2R$ and quartic potential $λϕ^4/4$ for several cases: real scalar inflaton, complex scalar inflaton and Abelian Higgs inflaton. We point out that the preheating proceeds much more violently than previously thought. If the inflaton is a complex scalar, the phase degree of freedom is violently produced at the first stage of preheating. If the inflaton is a Higgs field, the longitudinal gauge boson production is similarly violent. This is caused by a spike-like feature in the time dependence of the…
In a broad class of scenarios, inflation is followed by an extended era of matter-dominated expansion during which the inflaton condensate is nonrelativistic on subhorizon scales. During this phase density perturbations grow to the point of nonlinearity and collapse into bound structures. This epoch strongly resembles structure formation with ultra-light axion-like particles. This parallel permits us to adapt results from studies of cosmological structure formation to describe the nonlinear dynamics of this post-inflationary epoch. We show that the inflaton condensate fragments into "inflaton …
We analyze in detail the perturbative decay of the inflaton oscillating about a generic form of its potential $V(ϕ) = ϕ^k$, taking into account the effects of non-instantaneous reheating. We show that evolution of the temperature as a function of the cosmological scale factor depends on the spin statistics of the final state decay products when $k > 2$. We also include the inflaton-induced mass of the final states leading to either kinematic suppression or enhancement if the final states are fermionic or bosonic respectively. We compute the maximum temperature reached after inflation, the subs…
Inflation occurring at energy densities less than (10$^{14}$ GeV)$^4$ produces tensor perturbations too small to be measured by cosmological surveys. However, we show that it is possible to probe low scale inflation by measuring the mass of the inflaton at low energy experiments. Detection prospects and cosmological constraints are determined for low scale quartic hilltop models of inflation paired with a curvaton field, which imprints the spectrum of scalar perturbations observed in large scale structure and on the cosmic microwave background. With cosmological constraints applied, low scale …
We describe the coupling of matter fields to an inflationary sector of supergravity, the inflaton $Φ$ and a stabilizer $S$, in models where the Kahler potential has a flat inflaton direction. Such models include, in particular, advanced versions of the hyperbolic $α$-attractor models with a flat inflaton direction Kahler potential, providing a good fit to the observational data. If the superpotential is at least quadratic in the matter fields $U^{i}$, with restricted couplings to the inflaton sector, we prove that under certain conditions: i) The presence of the matter fields does not affect a…
We study the effects of particle production on the evolution of the inflaton field in an axion monodromy model with the goal of discovering in which situations the resulting dynamics will be consistent with the {\it swampland constraints}. In the presence of a modulated potential the evolving background field (solution of the inflaton homogeneous in space) induces the production of long wavelength inflaton fluctuation modes. However, this either has a negligible effect on the inflaton dynamics (if the field spacing between local minima of the modulated potential is large), or else it traps the…
We present a model where the inflaton field behaves like quintessence at late times, generating the present phase of accelerated expansion. This is achieved within the framework of warm inflation, in particular the Warm Little Inflaton scenario, where the underlying symmetries guarantee a successful inflationary period in a warm regime sustained by dissipative effects without significant backreaction on the scalar potential. This yields a smooth transition into a radiation-dominated epoch, at which point dissipative effects naturally shut down as the temperature drops below the mass of the fer…
A corpuscular quantum description of inflation shows that there is no fundamental problem with trans-Planckian excursions of the inflaton field up to about 100 Planck masses, with the upper bound coming from the corpuscular quantum effects. In this description the r-parameter measures the ratio of occupation numbers of gravitons versus inflatons, which, according to BICEP2, was roughly a half at the time of 60 e-foldings prior to the end of inflation. We stress that in non-Wilsonian UV self-completion of gravity any trans-Planckian mode coupled to inflaton is a black hole. Unlike the Wilsonian…
There is a wide consensus on the correct dynamics of the background in loop quantum cosmology. In this article we make a systematic investigation of the duration of inflation by varying what we think to be the most important "unknowns" of the model: the way to set initial conditions, the amount of shear at the bounce and the shape of the inflaton potential.
Trapped inflation is a mechanism in which particle production from the moving inflaton is the main source of friction in the inflaton equation of motion. The produced fields source inflaton perturbations, which dominate over the vacuum ones. We employ the set of equations for the inflaton zero mode and its perturbations which was developed in the original work on trapped inflation, and which we extend to second order in the perturbations. We build on this study by updating the experimental constraints, and by replacing the existing approximate solutions with more accurate ones. We obtain a dif…
We study radiative plateau-like inflation \& Z$_{BL}$-portal freeze-in fermionic dark matter (DM) in a minimal B-L extended model. The U(1)$_{B-L}$ Higgs, responsible for heavy neutrino masses, also drives inflation in the early universe, thanks to radiative corrections from the heavy neutrinos \& the Z$_{BL}$ gauge boson. In our benchmark choice for the U(1)$_{B-L}$ gauge coupling $g_{B-L}\sim10^{-4}$, a light Z$_{BL}$ boson can be explored by current and future lifetime frontier experiments, such as FASER and FASER 2 at the LHC, SHiP, Belle II and LHCb. For the benchmark, the Hubble scale of…
