We analyse the effect of the non-minimal coupling of the form $ξϕ^2R/2$ on the single field inflation. If the non-minimal coupling is large, it relaxes the constraint on the field self coupling, making it possible to use the Standard Model Higgs field as the inflaton. At the same time, even small non-minimal coupling constant, $ξ\gtrsim10^{-3}$, brings the usual inflaton with quartic potential in agreement with the WMAP5 observations.
Inflating curvaton can create curvature perturbation when the curvaton density is slowly varying. Using the delta-N formalism, we discuss the evolution of the curvature perturbation during curvaton inflation and find analytic formulation of the non-Gaussianity parameter. We first consider the inflating curvaton with sufficiently long inflationary expansion. Then we compare the result with short curvaton inflation.
We compute the distribution of sizes of inflating and non-inflating regions in an eternally inflating Universe. As a first illustrative problem, we study a simple scenario of an eternally inflating Universe in the presence of a massless scalar field $φ$ whose field values lie within some finite domain $φ\in(-φ_{cr},φ_{cr})$, with $\pmφ_{cr}$ marking the onset of thermalization/crunching. We compute many important quantities, including the fractal dimension, distribution of field values among inflating regions, and the number of inflating and non-inflating Hubble regions. With the aid of simula…
The primordial black hole (PBH) formation is studied in light of the inflating curvaton. The typical scale of the PBH formation is determined by curvaton inflation, which may generate PBH with $10^{14}\mathrm{g}\le M_\mathrm{PBH}\le 10^{38}\mathrm{g}$ when curvaton inflation gives the number of e-foldings $5\leq N_2\leq 38$. The non-Gaussianity of the inflating curvaton does not prevent the PBH formation.
We investigate in more depth the issue of backreaction in models that attempt at generating cosmological magnetic fields at inflation. By choosing different, physically motivated, parametrisations, we are able to isolate the core of the problem, namely the existence, alongside the wanted magnetic field, of its electric counterpart, which turns out quite generally to be stronger and redder. We were also able to identify a few more interwoven weak spots (the typically very high scale of inflation, the width of the spectrum of modes processed by inflation, the blindness of the amplification mecha…
We present a new solution to the hierarchy problem, where the Higgs mass is at its observed electroweak value because such a patch inflates the most in the early universe. If the Higgs mass depends on a field undergoing quantum fluctuations during inflation, then inflation will fill the universe with the Higgs mass that corresponds to the largest vacuum energy. The hierarchy problem is solved if the maximum vacuum energy occurs for the observed Higgs mass. We demonstrate this notion with a proof-of-principle model containing an axion, a modulus field and the Higgs, and show that inflation can …
In models of natural inflation, the inflaton is an axion-like particle. Unfortunately, axion potentials in UV-complete theories appear to be too steep to drive inflation. We show that, even for a steep potential, natural inflation can occur if the coupling between axion and gauge fields is taken into account. Due to this coupling, quanta of the gauge field are produced by the rolling of the axion. If the coupling is large enough, such a dissipative effect slows down the axion, leading to inflation even for a steep potential. The spectrum of perturbations is quasi-scale invariant, but in the si…
We present a field theory solution to the eta problem. By making the inflaton field the phase of a baryon of SU(N_c) supersymmetric Yang-Mills theory we show that all operators that usually spoil the flatness of the inflationary potential are absent. Our solution naturally generalizes to non-supersymmetric theories.
The idea of the strongly interacting field theories constitutes one of the pillars of the standard model of particle physics. The goal of this work is to export such theories to cosmology. Here we are interested in models in which the inflaton is a composite object, instead of a fundamental one. In so doing, we first construct the general setup, in the metric formulation, for generic models of composite inflation. We subsequently introduce the relevant examples in which the inflaton is identified with: A) the lightest (composite) scalar field in the minimal walking technicolor theory, and B) t…
The simplicity of the CMB data, so well described by single-field inflation, raises the question whether there might be an equally simple multi-field realization consistent with the observations. We explore the idea that an approximate 'angular' shift symmetry in field space (an isometry) protects the dynamics of coupled inflationary perturbations. This idea relates to the recent observation that multi-field inflation mimics the predictions of single-field inflation, if the inflaton is efficiently and constantly coupled to a second massless degree of freedom (the isocurvature perturbation). In…
The primordial curvature perturbation ζmay be generated by some curvaton field σ, which is negligible during inflation and has more or less negligible interactions until it decays. In the current scenario, the curvaton starts to oscillate while its energy density ρ_σis negligible. We explore the opposite scenario, in which ρ_σdrives a few e-folds of inflation before the oscillation begins. In this scenario for generating ζit is exceptionally easy to solve the ηproblem; one just has to make the curvaton a string axion, with anomaly-mediated susy breaking which may soon be tested at the LHC. The…
We point out that cosmological constraint from the axion isocurvature perturbation is relaxed if the Higgs field obtains a large field value during inflation in the DFSZ axion model. This scenario is consistent with the Higgs inflation model, in which two Higgs doublets have non-minimal couplings and play a role of inflaton.
We briefly review several Higgs inflation models and discuss their cosmological implications. We first classify the inflation models according to the predicted value of the tensor-to-scalar ratio: (i) $r = {\cal O}(0.01-0.1)$, (ii) $r = {\cal O}(10^{-3})$, and (iii) $r \ll 10^{-3}$. For each case we study (i) the Higgs inflation with a running kinetic term, (ii) the Higgs inflation with a non-minimal coupling to gravity, and (iii) the $B-L$ Higgs inflation. In the last case we introduce supersymmetry to suppress the Coleman-Weinberg corrections for successful inflation, and derive the upper bo…
Adopting a recently proposed single-superfield framework of supergravity inflation, we consider large field inflationary models in which MSSM Higgs-like fields play the role of the inflaton. In the simplest cases, the inflaton potential has a fractional power, which is different from that of the original Higgs inflation, and it can be tested by cosmological observations in near future. We find difficulties in identifying the inflaton with the MSSM Higgses and discuss possible candidates of the inflaton.
It is known that the Higgs potential becomes flat around the Planck scale under the assumption that the Standard Model is valid up to very high scale. Taking this into account, we revisit the Higgs inflation scenario and find that the various types of inflation occur depending on the value of the top mass. We also discuss the implication from non-supersymmetric string theory.
Most cosmological models of inflation are far away from providing a smoking gun at low energies. A model of Higgs inflation in the Next-to-Minimal Supersymmetric Standard Model, however, changes the NMSSM phenomenology drastically and may be well distinguished from the pure NMSSM or MSSM at a future Linear Collider. We point out certain differences of the inflationary model to the ordinary NMSSM and discuss the Higgs and neutralino/chargino sector in particular to identify the smoking gun of inflation at electroweak energies.
We consider a model of D-term inflation in which the inflaton coincides with the standard Higgs doublet. Non-renormalizable terms are controlled by a discrete R-symmetry of the superpotential. We consider radiative corrections to the scalar potential and find that Higgs inflation in the slow-roll approximation is viable and consistent with CMB data, although with a rather large value of the non-renormalizable coupling involved.
Signals of heavy particle production during inflation are encoded as non-analytic momentum scaling in primordial non-Gaussianity. These non-analytic signatures can be sourced by Standard Model particles with a modified Higgs scale uplifted by the slow-roll dynamics of inflation. We show that such a lifting mechanism becomes more efficient with the presence of a strong Higgs-inflaton mixing, where the Higgs mass scale is further increased by a small speed of sound in the effective theory of inflation. As a primary step towards detecting new particles in the cosmological collider program, non-Ga…
In this article, we intend to find a specific model which can satisfy the further refining dS swampland conjecture and scalar weak gravity conjecture (SWGC) simultaneously, in particular, Higgs inflation model and its two extensions: Higgs-Dilaton model and Palatini Higgs inflation. We find that although Higgs inflation model and Higgs-Dilaton model could satisfy the further refining dS swampland conjecture, the two models cannot satisfy SWGC and its strong version. While Palatini Higgs inflation could satisfy these conjectures simultaneously. Therefore Palatini Higgs inflation could be a "rea…
We re-examine large scalar fields within effective field theory, in particular focussing on the issues raised by their use in inflationary models (as suggested by BICEP2 to obtain primordial tensor modes). We argue that when the large-field and low-energy regimes coincide the scalar dynamics is most effectively described in terms of an asymptotic large-field expansion whose form can be dictated by approximate symmetries, which also help control the size of quantum corrections. We discuss several possible symmetries that can achieve this, including pseudo-Goldstone inflatons characterized by a …
We show that introducing $R^2$-term makes the Higgs-inflation and Higgs-dilaton inflation consistent models: the strong coupling energy scales in scalar, gauge and gravity sectors all are lifted up to the Planck scale.
We discuss a simple unitarization of Higgs inflation that is genuinely weakly coupled up to Planckian energies. A large non-minimal coupling between the Higgs and the Ricci curvature is induced dynamically at intermediate energies, as a simple ratio of mass scales. Despite not being dominated by the Higgs field, inflationary dynamics simulates the `Higgs inflation' one would get by blind extrapolation of the low-energy effective Lagrangian, at least qualitatively. Hence, Higgs inflation arises as an approximate `mirage' picture of the true dynamics. We further speculate on the generality of th…
Stimulated with the recent discovery of B-mode by BICEP2, we discuss the relation between a Higgs inflation and a chaotic inflation with quadratic potential. Starting with a generalized Higgs inflation model, we derive a condition for obtaining the quadratic chaotic inflation. It is shown that the running of the Higgs self-coupling constant in the Jordan frame plays a decisive role when the generalized Higgs inflation model coincides with the Higgs inflation model in a small-field limit.
We present three features which can be used to distinguish the R^2-inflation Higgs-inflation from with ongoing, upcoming and planned experiments, assuming no new physics (apart form sterile neutrinos) up to inflationary scale. (i) Slightly different tilt of the scalar perturbation spectrum n_s and ratio r of scalar-to-tensor perturbation amplitudes. (ii) Gravity waves produced within R^2-model by collapsing, merging and evaporating scalaron clumps formed in the post-inflationary Universe. (iii) Different ranges of the possible Standard Model Higgs boson masses, where the electroweak vacuum rem…
We consider the possibility to observationally differentiate the Standard Model (SM) Higgs driven inflation with non-minimal couplingto gravity from other variants of SM Higgs inflation based on the scalar field theories with non-canonical kinetic term such as Galileon-like kinetic term and kinetic term with non-minimal derivative coupling to the Einstein tensor. In order to ensure consistent results, we study the SM Higgs inflation variants by using the same method, computing the full dynamics of the background and perturbations of the Higgs field during inflation at quantum level. Assuming t…
We consider a simple extension of the Standard Model Higgs inflation with one new real scalar field which preserves unitarity up to the Planck scale. The new scalar field (called sigma) completes in the ultraviolet the theory of Higgs inflation by linearizing the Higgs kinetic term in the Einstein frame, just as the non-linear sigma model is unitarized into its linear version. The unitarity cutoff of the effective theory, obtained by integrating out the sigma field, varies with the background value of the Higgs field. In our setup, both the Higgs field and the sigma field participate in the in…
We study the generation of magnetic field in Higgs-inflation models where the Standard Model Higgs boson has a large coupling to the Ricci scalar. We couple the Higgs field to the Electromagnetic fields via a non- renormalizable dimension six operator suppressed by the Planck scale in the Jordan frame. We show that during Higgs inflation magnetic fields with present value $10^{-6}$ Gauss and comoving coherence length of $100 kpc$ can be generated in the Einstein frame. The problem of large back-reaction which is generic in the usual inflation models of magneto-genesis is avoided as the back-re…
We analyze the slow-roll inflation mechanism in brane framework with a real Higgs field confined on the brane. We prove that inflation occur for field value below the 4-dimensional Planck scale and produce cosmological perturbations in accordance with observations. Through the amplitude of the scalar perturbation produced during inflation we could determine the self-coupling constant of the Higgs field which is not predicted by the fundamental theories. Also it was found the solutions to the motion equations on the brane.
In the conventional metric formulation of gravity, the Higgs Inflation model violates unitarity in the electroweak vacuum in Higgs scattering at the energy scale $Λ\sim M_{Pl}/ξ$, where $ξ\sim 10^4$ is the non-minimal coupling of the Higgs to the Ricci scalar. In the Palatini formulation it is commonly believed that $Λ\sim M_{Pl}/\sqrtξ$, where $ξ\sim 10^{9}$. Here we reconsider unitarity violation in the electroweak vacuum in the Palatini formulation. We argue that there is no unitarity violation in Higgs scattering in the Palatini non-minimally coupled Standard Model in the electroweak vacuu…
We show that the Higgs portal interactions involving extra dark Higgs field can save generically the original Higgs inflation of the standard model (SM) from the problem of a deep non-SM vacuum in the SM Higgs potential. Specifically, we show that such interactions disconnect the top quark pole mass from inflationary observables and allow multi-dimensional parameter space to save the Higgs inflation, thanks to the additional parameters (the dark Higgs boson mass $m_ϕ$, the mixing angle $α$ between the SM Higgs $H$ and dark Higgs $Φ$, and the mixed quartic coupling) affecting RG-running of the …
We investigate the possibility of using the only known fundamental scalar, the Higgs, as an inflaton with minimal coupling to gravity. The peculiar appearance of a plateau or a false vacuum in the renormalised effective scalar potential suggests that the Higgs might drive inflation. For the case of a false vacuum we use an additional singlet scalar field, motivated by the strong CP problem, and its coupling to the Higgs to lift the barrier allowing for a graceful exit from inflation by mimicking hybrid inflation. We find that this scenario is incompatible with current measurements of the Higgs…
Higgs inflation is a simple and elegant model in which early-universe inflation is driven by the Higgs sector of the Standard Model. The Higgs sector can support early-universe inflation if it has a large nonminimal coupling to the Ricci spacetime curvature scalar. At energies relevant to such an inflationary epoch, the Goldstone modes of the Higgs sector remain in the spectrum in renormalizable gauges, and hence their effects should be included in the model's dynamics. We analyze the multifield dynamics of Higgs inflation and find that the multifield effects damp out rapidly after the onset o…
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.
The refined de Sitter derivative conjecture provides constraints to potentials that are low energy effective theories of quantum gravity. It can give direct bounds on inflationary scenarios and determine whether the theory is in the Landscape or the Swampland. We consider the `Higgs inflation' scenario taking the refined de Sitter derivative conjecture into account. Obtaining the critical lines for the potential, we find a conjecture parameter space in which the `Higgs inflation' is to be in the Landscape. Comparing with the model independent observational bounds from recent data we find that …
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 study Higgs inflation in the context of generalized G-inflation, i.e. the most general single-field inflation model with second-order field equations. The four variants of Higgs inflation proposed so far in the literature can be accommodated at one time in our framework. We also propose yet another class of Higgs inflation, the running Einstein inflation model, that can naturally arise from the generalized G-inflation framework. As a result, five Higgs inflation models in all should be discussed on an equal footing. Concise formulas for primordial fluctuations in these generalized Higgs inf…
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 consider the Higgs inflation in the extension of the Standard Model with two Higgs doublets coupled to gravity non-minimally. In the presence of an approximate global U(1) symmetry in the Higgs sector, both radial and angular modes of neutral Higgs bosons drive inflation where large non-Gaussianity is possible from appropriate initial conditions on the angular mode. We also discuss the case with single-field inflation for which the U(1) symmetry is broken to a Z_2 subgroup. We show that inflationary constraints, perturbativity and stability conditions restrict the parameter space of the Hig…
We investigate inflationary Higgs dynamics and constraints on the Standard Model parameters assuming the Higgs potential, computed to next-to-next leading order precision, is not significantly affected by new physics. For a high inflationary scale $H\sim 10^{14}$ GeV suggested by BICEP2, we show that the Higgs is a light field subject to fluctuations which affect its dynamics in a stochastic way. Starting from its inflationary value the Higgs must be able to relax to the Standard Model vacuum well before the electroweak scale. We find that this is consistent with the high inflationary scale on…
We discuss the inflationary dynamics of a system with a non-minimal coupling between the Higgs and the Ricci scalar as well as a Ricci scalar squared term. There are two scalar modes in this system, i.e. the Higgs and the spin-zero mode of the graviton, or the scalaron. We study the two-field dynamics of the Higgs and the scalaron during inflation, and clarify the condition where inflation is dominated by the Higgs/scalaron. We also find that the cut-off scale at around the vacuum is as large as the Planck scale, and hence there is no unitarity issue, although there is a constraint on the coup…
In the Higgs inflation scenario the Higgs field is strongly coupled to the Ricci scalar in order to drive primordial inflation. However, in its original form in pure metric formulation of gravity, the ultraviolet (UV) cutoff of the Higgs interactions and the Hubble rate are of the same magnitude, and this makes the whole inflationary evolution dependent of the unknown UV completion of the Higgs sector. This problem, the unitarity violation, plagues the Higgs inflation scenario. In this letter we show that, in the Palatini formulation of gravitation, Higgs inflation does not suffer from unitari…
We propose a realization of cosmic inflation with the Higgs field when the Higgs potential has degenerate vacua by employing the recently proposed idea of hillclimbing inflation. The resultant inflationary predictions exhibit a sizable deviation from those of the ordinary Higgs inflation.
A non-minimal coupling xi of the Standard Model Higgs field to gravity can give rise to inflation, but large xi is required and thus leads to a violation of perturbative unitarity at Mp/xi, which is well below the inflationary scale Mp/sqrt(xi). We re-examine this claim for a Higgs mass in the range 125-126 GeV for which lambda_eff(mu) runs to very small values near the Planck scale and can significantly reduce the value of xi required for inflation. Using the two-loop renormalization group equations and effective potential for Higgs xi-inflation, we find that familiar inflationary solutions c…
We consider how Higgs Inflation can be observationally distinguished from variants based on gauge singlet scalar extensions of the Standard Model, in particular where the inflaton is a non-minimally coupled gauge singlet scalar (S-inflation). We show that radiative corrections generally cause the spectral index n to decrease relative to the classical value as the Higgs mass is increased if the Higgs boson is the inflaton, whereas n increases with increasing Higgs mass if the inflaton is a gauge singlet scalar. The accuracy to which n can be calculated in these models depends on how precisely t…
The constraint on the mass of Higgs field in the Standard Model at the minimal interaction with the gravity is derived in the form of lower bound $m_H> 150$ GeV by the strict requirement of decoupling the Higgs boson from the inflation of early Universe: the inflation produced by the Higgs scalar could crucially destroy visible properties of large scale structure of Universe, while the large mass makes the Higgs particle not able to produce the inflation and shifts its cosmological role into the region of quantum gravity.
Current measurements of the Higgs boson mass and top Yukawa coupling suggest that the effective Higgs potential develops an instability below the Planck scale. If the energy scale of inflation is as high as the GUT scale, inflationary quantum fluctuations of the Higgs field can easily destabilize the standard electroweak vacuum and produce a lot of AdS domains. This destabilization during inflation can be avoided if a relatively large nonminimal Higgs-gravity or inflaton-Higgs coupling is introduced. Such couplings generate a large effective mass term for the Higgs, which can raise the effecti…
The Standard Model Higgs becomes tachyonic at high energy scales according to current measurements. This unstable regime of the Higgs potential can be realized in the early Universe during high scale inflation, potentially with catastrophic consequences. This letter highlights a crucial inherent feature of such configurations that has so far remained ignored: Higgs particle production out of vacuum induced by the rapidly evolving Higgs field, which gets exponentially enhanced due to the tachyonic instability. Such explosive particle production can rapidly drain energy away from the Higgs field…
In this letter we show that there is a unique non-minimal derivative coupling of the Standard Model Higgs boson to gravity such that: it propagates no more degrees of freedom than General Relativity sourced by a scalar field, reproduces a successful inflating background within the Standard Model Higgs parameters and, finally, does not suffer from dangerous quantum corrections.
