Inflationary Scenario Research Articles

Brane nucleation in supersymmetric models

This paper explores the process of vacuum decay in supersymmetric models related to flux compactifications. In particular, we describe these instabilities within supersymmetric Lagrangians for a single three-form multiplet. This multiplet combines scalar fields, representing the moduli fields in four dimensions, with 3-form fields that influence the potential for these moduli via the integer flux of their associated 4-form field strength. Furthermore, using supersymmetry as a guide we obtain the form of the couplings of these fields to the membranes that act as sources to the 3-form potentials. Adding small supersymmetry breaking terms to these Lagrangians one can obtain instanton solutions describing the decay of the vacua in these models by the formation of a membrane bubble. These instantons combine the usual Coleman-de Luccia and the Brown-Teitelboim formalisms in a single unified model. We study simple numerical examples of theories with and without gravity in this new framework and generalize known Euclidean methods to accomodate the simulataneous inclusion of scalar fields and charged membranes to these instanton solutions. Moreover, we show explicitly in these examples how one recovers the static supersymmetric solutions in the limiting case where the supersymmetry breaking terms vanish. In this limit, the bubble becomes infinite and flat and represents a hybrid between the usual supersymmetric domain walls of field theory models and the brane solutions interpolating between the supersymmetric vacua; a sort of dressed supermembrane BPS solution. Finally, we briefly comment on the implications of these solutions in cosmological models based on the String Theory Landscape where these type of 4d effective theories could be relevant in inflationary scenarios.

Cosmological models for [formula omitted] gravity

The Universe is currently in a phase of accelerated expansion, a fact that was experimentally proven in the late 1990s. Cosmological models involving scalar fields allow the description of this accelerated expansion regime in the Cosmos and present themselves as a promising alternative in the study of the inflationary eras, especially the actual one which is driven by the dark energy. In this work we use the f(R,T)−Λ(ϕ) gravity to find different cosmological scenarios for our Universe. We also introduce a new path to derive analytic cosmological models which may have a non-trivial mapping between f and T. We show that the analytic cosmological models obtained with this approach are compatible with a good description of the radiation era. In addition, we investigated the inflationary scenario and obtained a good agreement for the scalar spectral index ns. Concerning the tensor-to-scalar ratio r, we found promising scenarios compatible with current CMB data.

Reconstructing inflation and reheating in [formula omitted] gravity

In this work we study the reconstruction of an inflationary universe in the context of a theory of gravity f(ϕ)T, in which T corresponds to the trace of energy momentum tensor. To realize this reconstruction during the inflationary epoch, we consider as attractor the scalar spectral index ns in terms of the number of e-folds N, in the framework of the slow-roll approximation. By assuming a specific function f(ϕ) together with the simplest attractor ns(N), we find different expressions for the reconstructed effective potential V(ϕ). Additionally, we analyze the era of reheating occurs after of the reconstruction obtained during the inflationary epoch. In this scenario we determine the duration and temperature during the reheating epoch, in terms of the equation of state parameter and of the observational parameters. In this context, the different parameters associated to the reconstructed model are restricted during the scenarios of inflation and reheating by considering the recent astronomical observations.

Formation of trapped vacuum bubbles during inflation, and consequences for PBH scenarios

A class of inflationary scenarios for primordial black hole (PBH) formation include a small barrier in the slope of the potential. There, the inflaton slows down, generating an enhancement of primordial perturbations. Moreover, the background solution overcomes the barrier at a very low speed, and large backward quantum fluctuations can prevent certain regions from overshooting the barrier. This leads to localized bubbles where the field remains “trapped” behind the barrier. In such models, therefore, we have two distinct channels for PBH production: the standard adiabatic density perturbation channel and the bubble channel. Here, we perform numerical simulations of bubble formation, addressing the issues of initial conditions, critical amplitude and bubble expansion. Further, we explore the scaling behaviour of the co-moving size of bubbles with the initial amplitude of the field fluctuation. We find that for small to moderate non-Gaussianity f NL ≲ 2.6, the threshold for the formation of vacuum bubbles agrees with previous analytical estimates [1] to 5% accuracy or so. We also show that the mass distribution for the two channels is different, leading to a slightly broader range of PBH masses when both contributions are comparable. The bubble channel is subdominant for small f NL, and becomes dominant for f NL ≳ 2.6. We find that the mass of PBHs in the bubble channel is determined by an adiabatic overdensity surrounding the bubble at the end of inflation. Remarkably, the profile of this overdensity turns out to be of type-II. This represents a first clear example showing that overdensities of type-II can be dominant in comparison with the standard type-I. We also comment on exponential tails and on the fact that in models with local type non-Gaussianity (such as the one considered here), the occurrence of alternative channels can easily be inferred from unitarity considerations.

Theoretical and observational prescription of warm-inflation in FLRW universe with torsion

The paper deals with Warm Inflationary scenario in FLRW with torsion both from theoretical and observational point of view. In the background of flat FLRW model the Hubble parameter is found to be proportional to the torsion function and warm inflation is examined both in weak and strong dissipation regimes for the power law choice of potential using slow-roll approximation with quasi-stable criteria for radiation. The slow-roll parameters, no.of e-folds, scalar spectral index, and tensor-to-scalar ratio are determined in the present model for mainly three choices of the dissipation coefficient Gamma using the Planck data set. Finally, we focus on single-field chaotic quartic potential with the above choices of the dissipation coefficient to confront the warm inflation observational predictions directly with the latest observational data set.

Cosmology inflation in viscous mimetic f(R,T) gravity

We investigate in this work the inflationary scenario in viscous [Formula: see text] gravity formalism with mimetic potential and Lagrange multiplier. Considering that our universe contains beside a perfect fluid, a dark energy and a bulk viscous fluid, we obtain through the modified Friedmann equations a main differential equation that may describe the cosmological evolution in viscous mimetic [Formula: see text] gravity. For particular choice of the model [Formula: see text] and for two forms of bulk viscosity coefficient, one as function of the Hubbe parameter [Formula: see text] and the other, as density-dependent viscosity, we present a numerical results of the inflationary parameters such as the tensor-to-scalar ratio [Formula: see text] and the scalar spectral index [Formula: see text]. A comparison of these results with observational data shows that our model can be used to describe the accelerated expansion of the universe.

Primordial black holes and inflation from double-well potentials

We investigate the formation of large peaks in the inflationary curvature power spectrum from double-well potentials. In such scenarios, the initial CMB spectrum is created at large field values. Subsequently, the inflaton will cross one of the minima and will decelerate rapidly as it reaches the local maximum at the origin, either falling back or crossing it. During this final phase, a significant peak in the curvature power spectrum can be generated. Our analysis reveals that this class of models produces more pronounced peaks than most quasi-inflection point scenarios with less tuning for the model parameters. Finally, we construct an explicit theoretically motivated inflationary scenario that is consistent with the latest CMB observations and capable of generating sufficiently large curvature perturbations for primordial black holes.

The cosmological model in [formula omitted] gravity with Scalar Field conformity

The homogeneous and isotropic cosmological model in generalized f(R,Tϕ) theories associated with the scalar field is discussed, which is motivated by the f(R,T) theory of gravity studied by Harko et al. (2011), Harko (2014) [1,2]. The f(R,Tϕ) gravity can be explained as f(R,T) gravity with a self-interacting scalar field ϕ, where Tϕ is the trace of the energy–momentum tensor. The parametrization of Hubble parameter H(t) is taken as α−βe−γt, where α, β, and γ are arbitrary constants such that α,γ>0, and β<0. The model shows no space–time singularity, and the expansion of the universe will continue forever, i.e., the future scenario of the universe attains Big Freeze. The model predicts the moderate inflationary scenario at the time of the evolution of the universe, and it is consistent with ΛCDM in the late times. The consistency of the model has also been examined using the recent observational Hubble dataset and supernovae dataset. Finally, the physical features of the model have been discussed in some detail.

Nonlinear sigma models in inflationary cosmology

Nonlinear Sigma Models in two dimensions ([Formula: see text]) describe the quantum-field theory (QFT) of the Embedding map from a two-dimensional surface to a higher dimensional target space. We assume that before the big bang the universe was an abstract space with a two-dimensional surface embedded in it. We study QFT of the Embedding map in the universe that is [Formula: see text]. We consider the abstract target space which is a Lie Group; SU(3) manifold. Then taking a symmetry breaking potential in [Formula: see text] QFT, we show the emergence of a geometric arrow of time via a big bang. This leads to an inflationary scenario driven by the Embedding map. We also discuss the mathematical existence of a [Formula: see text] and some aspects of the renormalization group flow in [Formula: see text] relevant to inflation.

A non-linear model of public debt with bonds and money finance

In this paper, we study the dynamic relationship between the public debt ratio and the inflation rate. Using a non-linear macroeconomic model of difference equations, we analyze the role of monetary and fiscal policy in influencing the stability of the debt ratio and inflation. We get three main results. First, we find that, in a low inflation scenario, money finance can be helpful in stabilizing the debt ratio. Second, we show that in a dynamic setting, standard Taylor rules may not be sufficient to control inflation. The Central Bank’s credibility in driving inflation expectations is indeed crucial to control price developments and to achieve macroeconomic stability. Finally, an active budget adjustment rule has a stabilizing effect on the debt ratio, even if it may not be enough to avoid explosive patterns. Notably, the stability of the steady state depends on the fine-tuning of the policy mix. One of the novelties of our analysis is the presence of a threshold level for the debt ratio and inflation, beyond which the debt ratio becomes unsustainable following an explosive path. The distance between this threshold and the steady state can be considered a proxy of the robustness of the economy to exogenous shocks.

Estimation of imprints of the bounce in loop quantum cosmology on the bispectra of cosmic microwave background

Primordial non-Gaussianity has set strong constraints on models of the early universe.Studies have shown that Loop Quantum Cosmology (LQC), which is an attempt to extend inflationary scenario to planck scales, leads to a strongly scale dependent and oscillatory non-Gaussianity. In particular, the non-Gaussianity function f NL (k 1, k 2, k 3) generated in LQC, though similar to that generated during slow roll inflation at small scales, is highly scale dependent and oscillatory at long wavelengths. In this work, we investigate the imprints of such a primordial bispectrum in the bispectrum of Cosmic Microwave Background (CMB).Inspired by earlier works, we propose an analytical template for the primordial bispectrum in LQC.We write the template as a sum of strongly scale dependent and oscillatory part, which captures the contribution due to the bounce, and a part which captures the scale invariant behaviour similar to that of slow roll. We then compute the reduced bispectra of temperature and electric polarisation and their three-point cross-correlations corresponding to these two parts.We show that the contribution from the bounce to the reduced bispectrum is negligible compared to that from the scale-independent part. Thus, we conclude that the CMB bispectra generated in LQC will be similar to that generated in slow roll inflation. We conclude with a discussion of our results and its implications to LQC.

Constant-roll and primordial black holes in f(Q,T) gravity

In this study, we investigate the consequence of the constant-roll condition and examine the role of a chosen form of f(Q,T) gravity, given by f(Q,T)=αQ2+σT, in the cosmological inflation process. We analyze the inflationary scenario by calculating modified Friedmann equations and giving an alternative technique that enables relating modified slow-roll parameters to the constant roll parameter β. Considering both chaotic and hilltop models, we calculate the spectral index and the tensor-to-scalar ratio and compare their compatibility with Planck’s data for different choices of the constant roll parameter β. We examine the evolution of primordial black holes in our chosen modified gravity model taking into account the accretion process and the evaporation due to Hawking radiation. We compute the evaporation and accretion masses rate and provide an analytic estimation of the primordial black holes mass and of the radiation in the f(Q,T) gravity model.

Inflation caused by a potential valley with 𝖢𝖯 violation

We propose an inflation scenario caused by an inflaton identified with a potential valley which brings about CP violation in the standard model (SM). If singlet scalars have nonminimal couplings with the Ricci scalar in a suitable way, favorable inflation could be derived through the potential valley composed of such scalars. We study dynamics of the scalars during and after the inflation, which suggests that it could be described as a single field inflation approximately. If these scalars make suitable ingredients of the SM couple with vectorlike fermions and right-handed neutrinos, a CKM phase could be induced and also leptogenesis could occur successfully even at a rather low reheating temperature.

Thermodynamics of warm axionic Abelian gauge inflation

Inflationary spectral index from the Langevin equation is calculated under the frame of warm inflationary scenario with inflaton interacting with U(1) gauge fields through the Chern–Simons coupling ∝ ϕ F μ ν F ∼ μ ν / f . Under the strong dissipative condition, the spectral index is calculated in terms of the ratio of Hubble parameter to temperature H/T. Then relation between H/T and other cosmic parameters is analytically expressed, based on which a spectral index related to the Chern–Simons coupling strength is further obtained. Numerical results show that cosmic temperature T closes to a constant during inflation and decreases after inflation without a reheating process. Meanwhile, the ratio H/T tends to a constant if the gauged coupling constant is less than a threshold. This phenomenon shows that cosmic temperature may be an important physical parameter with a special value and adiabatic approximation still holds. We obtain the estimate H/T ≤ 0.3377 during inflation from Planck data and other constraint conditions.

Nonminimally-coupled warm Higgs inflation: Metric vs. Palatini formulations

In this work, we study the non-minimally-coupled Higgs model in the context of warm inflation scenario on both metric and Palatini approaches. We particularly consider a dissipation parameter of the form Γ=CTT with CT being a coupling parameter and focus only on the strong regime of the interaction between inflaton and radiation fluid. We compute all relevant cosmological parameters and constrain the models using the observational Planck 2018 data. We discover that the ns and r values are consistent with the observational bounds. Having used the observational data, we constrain a relation between ξ and λ for the non-minimally-coupled warm Higgs inflation in both metric and Palatini cases. To produce ns and r in agreement with observation, we find that their values are two orders of magnitude higher than those of the usual (cold) non-minimally-coupled Higgs inflation.

Reconstruction of inflationary scenarios in non-conservative unimodular gravity

ABSTRACT Unimodular gravity is an alternative theory of gravity to general relativity. The gravitational field equations are given by the trace-free version of Einstein’s field equations. Due to the structure of the theory, unimodular gravity admits a diffusion term that characterizes a possible non-conservation of the canonical energy–momentum tensor locally. Employing this feature of unimodular gravity, in this work, we explicitly show how to construct an inflationary phase that can be contrasted with current observations. In particular, we focus on three different inflationary scenarios of physical interest. An important element in these scenarios is that the accelerated expansion is driven by the diffusion term exclusively, i.e. there is no inflaton. Furthermore, the primordial spectrum during inflation is generated by considering inhomogeneous perturbations associated to standard hydrodynamical matter (modelled as a single ultra-relativistic fluid). For each of the scenarios, we obtain the prediction for the primordial spectrum and contrast it with recent observational bounds using Planck 2018 + Bicep2/KECK Array data.

Causes and lessons of accelerating global inflation

The world economy has recently experienced a strong inflationary shock, which the leading research institutions and central banks were unable to predict. In advanced economies inflation rates spiked up to levels had not been seen for decades. Inflation also hit emerging economies albeit the shocks of such magnitude are more common for the countries of this group. What was the reason of the inflationary wave of 2021-2002 and why was it unexpected? In the paper we propose that the main driver of inflation was the rapid recovery of aggregate demand while aggregate supply lagged behind since it was negatively affected by quarantine restrictions and supply chain disruptions. A sharp increase in the prices of food and energy contributed to inflation significantly. Unprecedented fiscal stimulus supported by liquidity injections from central banks was also an important factor in boosting demand and accelerating inflation. Sharp turn towards ultra­loose monetary and fiscal policy can be largely attributed to the experience of the previous decade which showed that inflation in advanced economies remained below the target level, despite constant stimulus. We discuss arguments considered by central banks when they kept monetary policy soft even after inflation significantly exceeded the target levels. Finally, we briefly discuss scenarios of possible future inflation, including a stagflation scenario, and analyze their underlying factors.

Warm inflation in [formula omitted] gravity

In this work, we explored warm inflation in the background of f(R,T) gravity in the strong dissipation regime. Considering scalar field for FLRW universe, we derived modified field equations. We then deduced slow-roll parameters under slow-roll approximations followed by power spectrum for scalar and tensor perturbations and their corresponding spectral indices. We have considered Chaotic and Natural potentials and estimated scalar spectral index and tensor-to-scalar ratio for constant as well as variable dissipation factor Γ. We found that both the rejected potentials can be revived under the context of f(R,T) gravity with suitable choice of the model parameters. Further, it is seen that within the warm inflationary scenario both the potentials can yield result consistent with Planck 2018 and BICEP/Keck bounds at the Planckian and sub-Planckian energy scales.

Policy Forum: The Impact of a Rise in Inflation on Marginal Effective Tax Rates on Corporate Capital

The purpose of this article is to discuss the impact of inflation on the incentive effects of the corporate income tax in Canada. Illustrative calculations of the marginal effective tax rate (METR) on capital are provided under two inflation scenarios: 2 percent and 4 percent. It is shown that while there are counteracting effects, on balance higher inflation tends to increase the METR on capital. More importantly, higher inflation increases the variability in METRs across assets and sectors. This increase in interasset and intersectoral distortions has important efficiency implications for the Canadian economy.

Population mortality impacts of the rising cost of living in Scotland: scenario modelling study

IntroductionTo inform policymaking, it is important to understand the population health impacts of recent increased inflation, and of measures implemented to mitigate these.MethodsWe used scenario modelling to estimate (a) how...