Plateau Inflation Research Articles

Study in the non-canonical domain of power law Plateau inflation

The recent Cosmic Microwave Background (CMB) observations are pointing towards a plateau feature in the flat potential of the inflation field to drive the initial acceleration of the Universe. In this regard, Dimopoulos and Owen introduced a very promising model dubbed as Power Law Plateau inflation (PLP) (Dimopoulos and Owen, 2016) which has this feature in it. But to make this model consistent with observation in the standard cold inflationary scenario, one needs to introduce an epoch of thermal inflation. In this paper, we have shown realizing this model in the non-canonical domain, could actually make the model consistent with the observation without introducing any late-stage thermal inflation. We also report the constraints from the Cosmic Microwave Background observations on the reheating parameter that one can associate with the model parameter.

Radiative plateau inflation with conformal invariance: Dynamical generation of electroweak and seesaw scales

We investigate a scale-invariant $B-L$ scenario where the Standard Model (SM) is supplemented with a dark scalar $\phi$ which has gauge \& Yukawa interactions, with the couplings $g_{BL}$ and $y$, respectively, leading to radiative plateau inflation at scale $\phi=M$ in the ultraviolet (UV), while dynamically generating the Electroweak and Seesaw scales \textit{\'a l\'a} Coleman-Weinberg in the infrared (IR). This is particularly achieved by implementing threshold corrections at an energy scale $\mu_T$ arising due to the presence of vector-like fermions. We show that implementing the inflationary observables makes the couplings solely dependent on the plateau scale $M$, leaving us with only two independent parameters $M$ and $\mu_T$. Within the theoretically consistent parameter space defined by $m_{Z_{BL}} > 850~\rm GeV$, from the assumption of independent evolution of the dark sector couplings from the SM couplings and $M < 5.67~M_P$ required for the realisation of inflationary \textit{plateau-like} behaviour of the potential around $\phi=M$, where $M_P=2.4\times10^{18}$ GeV is the reduced Planck mass, we identify the parameter space that is excluded by the current LHC results from the search for the heavy $Z_{BL}$ boson. For typical benchmark points in the viable parameter regions, we estimate the reheating temperature to be $\mathcal{O}(TeV)$ thus consistent with the standard Big Bang Nucleosynthesis (BBN) constraints. For typical benchmark points ($M=5.67,~1,~0.1~M_P$) we predict the scales of inflation to be $\mathcal{H}_{inf}=2.79\times10^{12}$ GeV, $1.53\times10^{10}$ GeV and $1.53\times10^7$ GeV, respectively.

Dynamics of constant sound speed inspires warm inflation

In this work, we consider a modern form of single-field inflationary models (known as power-law plateau inflation and preheating phase for a class of plateau inflationary model) and ASPIC models by considering the Dirac–Born–Infeld (DBI) non-canonical scalar field in the light of warm inflationary scenario. For these models, we assume constant sound speed [Formula: see text] and compute different slow-roll [Formula: see text], [Formula: see text] and [Formula: see text] as well as inflationary parameters (number of [Formula: see text]-folds [Formula: see text], spectral index [Formula: see text], scalar spectral index [Formula: see text] and tensor-to-scalar ratio [Formula: see text]) for specific anti-de Sitter warp factor of the DBI inflation. Next, we plot the trajectories of [Formula: see text], [Formula: see text] and [Formula: see text] with different choices of [Formula: see text] and found the ranges [Formula: see text], [Formula: see text], [Formula: see text] (for minimal inflation model), [Formula: see text], [Formula: see text], [Formula: see text] (for modified minimal inflation model) and [Formula: see text], [Formula: see text], [Formula: see text] (mixed large field inflation), respectively. Moreover, the ranges of these parametric plots for power-law plateau inflationary model are [Formula: see text], [Formula: see text], [Formula: see text]. Finally, we find that the results of all these parametric plots are consistent with 68% and 95% with current observational data except scalar-to-tensor ratio [Formula: see text] for modified minimal and power-law Plateau inflation models.

Tachyonic preheating in plateau inflation

Plateau inflation is an experimentally consistent framework in which the scale of inflation can be kept relatively low. Close to the edge of the plateau, scalar perturbations are subject to a strong tachyonic instability. Tachyonic preheating is realized when, after inflation, the oscillating inflaton repeatedly re-enters the plateau. We develop the analytic theory of this process and expand the linear approach by including backreaction between the coherent background and growing perturbations. For a family of plateau models, the analytic predictions are confronted with numerical estimates. Our analysis shows that the inflaton fragments in a fraction of an e-fold in all examples supporting tachyonic preheating, generalizing the results of previous similar studies. In these scenarios, the scalar-to-tensor ratio is tiny, r < 10-7.

Gravitational dark matter production in Palatini preheating

We study preheating in plateau inflation in the Palatini formulation of general relativity, in a special case that resembles Higgs inflation. It was previously shown that the oscillating inflaton field returns to the plateau repeatedly in this model, and this leads to tachyonic production of inflaton particles. We show that a minimally coupled spectator scalar field can be produced even more efficiently by a similar mechanism. The mechanism is purely gravitational, and the scalar field mass can be of order 1013 GeV, larger than the Hubble scale by many orders of magnitude, making this a candidate for superheavy dark matter.

Power law plateau inflation potential in the RS II braneworld evading swampland conjecture

In the recent time, inflationary cosmology is facing an existential crisis due to the proposed Swampland criterion which aims to evade any (meta-)stable de Sitter construction within the String landscape. It is been realised that a single field slow roll inflation is inconsistent with the Swampland criterion unless the inflationary model is realised in some non-standard scenario such as Warm inflation or the Braneworld scenario. Dimopoulos and Owen (Phys Rev D 94(6): 063518, 2016) introduced a new class of model of inflation dubbed as the power law plateau inflation in the standard cold inflationary scenario. But to realise this model in the standard scenario consistent with observation, they had to introduce a phase of thermal inflation. In this paper we have analysed this model in the braneworld scenario to show that for some choice of the parameters defining the model class, one can have an observationally consistent power law plateau without any phase of thermal inflation. We have also shown that, for the correct choice of model parameters, one can easily satisfy the Swampland criterion. Besides, for correct choice of equation of states (w_{re}), one can also satisfy the recently proposed Trans–Planckian Censorship Conjecture (TCC).

Supergravity Model of Inflation and Explaining IceCube HESE Data via PeV Dark Matter Decay

We construct a unified model of inflation and PeV dark matter with an appropriate choice of no-scale Kähler potential, superpotential, and gauge kinetic function in terms of MSSM fields and hidden sector Polonyi field. The model is consistent with the CMB observations and can explain the PeV neutrino flux observed at IceCube HESE. A Starobinsky-like Higgs-sneutrino plateau inflation is obtained from the D-term SUGRA potential while F-term being subdominant during inflation. To get PeV dark matter, SUSY breaking at PeV scale is achieved through Polonyi field. This sets the scale for soft SUSY breaking parameters m0,m1/2,A0 at the GUT scale in terms of the parameters of the model. The low-energy particle spectrum is obtained by running the RGEs. We show that the ~125 GeV Higgs and the gauge coupling unification can be obtained in this model. The 6 PeV bino-type dark matter is a subdominant fraction (~11%) of the relic density, and its decay gives the PeV scale neutrino flux observed at IceCube by appropriately choosing the couplings of the R-parity violating operators. Also, we find that there is degeneracy in scalar field parameters γ,β and coupling ζ value in producing the correct amplitude of CMB power spectrum. However, the value of parameter tanβ=1.8, which is tightly fixed from the requirement of PeV scale SUSY breaking, removes the degeneracy in the values of the scalar field parameters to provide a unique solution for inflation. In this way, it brings the explanation for dark matter, PeV neutrinos, and inflation within the same framework.

Initial conditions for plateau inflation: a case study

We study initial conditions for inflation in scenarios where the inflaton potential has a plateau shape. Such models are those most favored by Planck data and can be obtained in a large number of model classes. As a representative example, we consider Higgs inflation with and without an R2 term in the context of Palatini gravity. We show that inflation with a large number of e-folds generically occurs in a large part of the parameter space without any fine-tuning of parameters even when the scale of inflation and the inflaton field value during inflation are much smaller than the Planck scale. We discuss consequences for detection of primordial gravitational waves and spectral tilt of curvature perturbations, as well as the recently proposed “Trans-Planckian Censorship” conjecture.

(P)reheating after minimal plateau inflation and constraints from CMB

In this paper we have investigated the preheating phase for a class of plateau inflationary model considering the four-legs interaction term (1/2)g2ϕ2χ2 between the inflaton (ϕ) and reheating field (χ). We specifically focus on the effects of our model parameter ϕ* which controls inflationary dynamics. For ϕ* < Mp, the departure of the inflaton potential from the usual power-law behavior ϕn significantly modifies the microscopic behavior of the preheating dynamics. We analyze and compare the efficiency of production, thermalization behavior and the final equation of states of the system for different values of n = 2,4,6 considering two different values of ϕ*. Most importantly as we increase n, or decrease ϕ*, the preheating occurs very efficiently with the final equation of state to be that of the radiation, w = 1/3. However, for n = 2, the final equation of state turned out to be w ≃ 0.2. In the non-perturbative framework complete decay of inflaton could not be achieved with the four-legs interaction for any model under consideration. Therefore, in order to complete the reheating process, we perform the perturbative analysis for the second stage of the reheating phase. With the appropriate initial condition set by the non-perturbative dynamics, we solved a set of homogeneous Boltzmann equations for both the fields supplemented by the constraints coming from the subsequent entropy conservation. In so doing, we calculated the reheating temperature which was otherwise ill-defined right after the end of preheating. The temperature can be uniquely fixed for a given inflaton decay constant and the CMB temperature. We also compare our results with the conventional reheating constraint analysis and discuss the limits on the inflaton decay constant from the field theory perspective.

CMB constraints on dark matter phenomenology via reheating in minimal plateau inflation

We consider the CMB constraints on reheating and dark matter parameter space for a specific plateau type inflationary model. The plateau inflationary models which are currently most favored models from data can be well approximated by a potential of the form $V(\phi)\propto \phi^n$ around $\phi=0$. This fact makes it possible to study the reheating phase with general inflaton equation of state in a viable cosmological scenario. In addition, following our recent work[1], we generalize the connection between reheating and the present CMB data and the dark matter parameter space for general inflaton equation of state parameter.

Dynamics of warm power-law plateau inflation with a generalized inflaton decay rate: predictions and constraints after Planck 2015

In the present work, we study the consequences of considering a new family of single-field inflation models, called power-law plateau inflation, in the warm inflation framework. We consider the inflationary expansion is driven by a standard scalar field with a decay ratio Gamma having a generic power-law dependence with the scalar field phi and the temperature of the thermal bath T given by Gamma (phi ,T)=C_{phi }frac{T^a}{phi ^{a-1}}. Assuming that our model evolves according to the strong dissipative regime, we study the background and perturbative dynamics, obtaining the most relevant inflationary observable as the scalar power spectrum, the scalar spectral index and its running and the tensor-to-scalar ratio. The free parameters characterizing our model are constrained by considering the essential condition for warm inflation, the conditions for the model evolves according to the strong dissipative regime and the 2015 Planck results through the n_mathrm{s}–r plane. For completeness, we study the predictions in the n_mathrm{s}–mathrm{d}n_mathrm{s}/mathrm{d}ln k plane. The model is consistent with a strong dissipative dynamics and predicts values for the tensor-to-scalar ratio and for the running of the scalar spectral index consistent with current bounds imposed by Planck and we conclude that the model is viable.

Plateau inflation in R-parity violating MSSM

Inflation with plateau potentials give the best fit to the CMB observables as they predict tensor to scalar ratio stringently bounded by the observations from Planck and BICEP2/Keck. In supergravity models it is possible to obtain plateau potentials for scalar fields in the Einstein frame which can serve as the inflation potential by considering higher dimensional Planck suppressed operators and by the choice of non-canonical K\"ahler potentials. We construct a plateau inflation model in MSSM where the inflation occurs along a sneutrino-Higgs flat direction. A hidden sector Polonyi field is used for the breaking of supersymmetry after the end of the inflation. The proper choice of superpotential leads to strong stabilization of the Polonyi field, $m_{Z}^2\gg m_{3/2}^2$, which is required to solve the cosmological moduli problem. Also, the SUSY breaking results in a TeV scale gravitino mass and scalar masses and gives rise to bilinear and triliear couplings of scalars which can be tested at the LHC. The sneutrino inflation field can be observed at the LHC as a TeV scale diphoton resonance like the one reported by CMS and ATLAS.

Constraining curvatonic reheating

We derive the first systematic observational constraints on reheating in models of inflation where an additional light scalar field contributes to primordial density perturbations and affects the expansion history during reheating. This encompasses the original curvaton model but also covers a larger class of scenarios. We find that, compared to the single-field case, lower values of the energy density at the end of inflation and of the reheating temperature are preferred when an additional scalar field is introduced. For instance, if inflation is driven by a quartic potential, which is one of the most favoured models when a light scalar field is added, the upper bound Treh < 5 × 104 GeV on the reheating temperature Treh is derived, and the implications of this value on post-inflationary physics are discussed. The information gained about reheating is also quantified and it is found that it remains modest in plateau inflation (though still larger than in the single-field version of the model) but can become substantial in quartic inflation. The role played by the vev of the additional scalar field at the end of inflation is highlighted, and opens interesting possibilities for exploring stochastic inflation effects that could determine its distribution.

Plateau inflation in SUGRA-MSSM

We explored a Higgs inflationary scenario in the SUGRA embedding of the MSSM in Einstein frame where the inflaton is contained in the $SU(2)$ Higgs doublet. We include all higher order non-renormalizable terms to the MSSM superpotential and an appropriate K\"ahler potential which can provide slow-roll inflaton potential in the $D-$flat direction. In this model, a plateau-like inflation potential can be obtained if the imaginary part of the neutral Higgs acts as the inflaton. The inflationary predictions of this model are consistent with the latest CMB observations. The model represents a successful Higgs inflation scenario in the context of Supergravity and it is compatible with Minimal Supersymmetric extension of the Standard Model.

Plateau inflation from random non-minimal coupling

A generic non-minimal coupling can push any higher-order terms of the scalar potential sufficiently far out in field space to yield observationally viable plateau inflation. We provide analytic and numerical evidence that this generically happens for a non-minimal coupling strength ξ of the order N2e. In this regime, the non-minimally coupled field is sub-Planckian during inflation and is thus protected from most higher-order terms. For larger values of ξ, the inflationary predictions converge towards the sweet spot of PLANCK. The latter includes ξ ≃ 104 obtained from CMB normalization arguments, thus providing a natural explanation for the inflationary observables measured.

Radiative plateau inflation

We describe how monomial chaotic inflation becomes compatible with the latest CMB data thanks to radiative corrections producing a plateau. The interactions of the inflation with other fields, required for reheating, can flatten the potential and moderate the production of primordial gravitational waves, keeping these below the current upper bound. We show that the appearance of a plateau requires that the inflaton couples to fermions and to another scalar or a gauge group. We give concrete examples of minimal particle physics models leading to plateaus for quadratic and quartic chaotic inflation. We also provide a three-parameter model-independent description of radiatively corrected inflation that is amenable to CMB analyses.

The Hubble flow of plateau inflation

In the absence of CMB precision measurements, a Taylor expansion has often been invoked to parametrize the Hubble flow function during inflation. The standard ``horizon flow'' procedure implicitly relies on this assumption. However, the recent Planck results indicate a strong preference for plateau inflation, which suggests the use of Padé approximants instead. We propose a novel method that provides analytic solutions of the flow equations for a given parametrization of the Hubble function. This method is illustrated in the Taylor and Padé cases, for low order expansions. We then present the results of a full numerical treatment scanning larger order expansions, and compare these parametrizations in terms of convergence, prior dependence, predictivity and compatibility with the data. Finally, we highlight the implications for potential reconstruction methods.