Cosmic Inflation Research Articles

Cosmic inflation and (g-2) μ in minimal gauged Lμ-Lτ model

The minimal U(1) Lμ - Lτ gauge symmetry extended Standard Model (SM) is a well motivated framework that resolves the discrepancy between the theoretical prediction and experimental observation of muon anomalous magnetic moment. We envisage the possibility of identifying the beyond Standard Model Higgs of U(1) Lμ - Lτ sector, non-minimally coupled to gravity, as the inflaton in the early universe, while being consistent with the (g-2)μ data. Although the structure seems to be trivial, we observe that taking into consideration of a complete cosmological history starting from inflation through the reheating phase to late-time epoch along with existing constraints on U(1) Lμ - Lτ gauge symmetry extended Standard Model (SM) is a well motivated framework that resolves the discrepancy between the theoretical prediction and experimental observation of muon anomalous magnetic moment. We envisage the possibility of identifying the beyond Standard Model Higgs of U(1) Lμ Lτ model parameters leave us a small window of allowed reheating temperature. This further results into restriction of (n s -r) plane which is far severe than the one in a generic non-minimal quartic inflationary set up.

Clocking the end of cosmic inflation

Making observable predictions for cosmic inflation requires determining when the wavenumbers of astrophysical interest today exited the Hubble radius during the inflationary epoch. These instants are commonly evaluated using the slow-roll approximation and measured in e-folds Δ N=N - N end, in reference to the e-fold N end at which inflation ended. Slow roll being necessarily violated towards the end of inflation, both the approximated trajectory and N end are determined at, typically, one or two e-folds precision. Up to now, such an uncertainty has been innocuous, but this will no longer be the case with the forthcoming cosmological measurements. In this work, we introduce a new and simple analytical method, on top of the usual slow-roll approximation, that reduces uncertainties on ΔN to less than a tenth of an e-fold.

Vanilla inflation predicts negative running

We show that the simplest, and currently favoured, theoretical realizations of cosmic inflation yield a sharp prediction for the running of the spectral index . Using latest cosmological data, we compute its marginalized posterior probability distribution over the space of nearly 300 models of single-field slow-roll inflation. The most probable value is , lying within the credible interval . Within the landscape of all the proposed slow-roll inflationary models, positive values for the running are therefore disfavoured at more than three-sigma.

Gravitational wave signatures of post-fragmentation reheating

After cosmic inflation, coherent oscillations of the inflaton field about a monomial potential V(ϕ) ∼ ϕ k result in an expansion phase characterized by a stiff equation-of-state w ≃ (k-2)/(k+2). Sourced by the oscillating inflaton condensate, parametric (self)resonant effects can induce the exponential growth of inhomogeneities eventually backreacting and leading to the fragmentation of the condensate. In this work, we investigate realizations of inflation giving rise to such dynamics, assuming an inflaton weakly coupled to its decay products. As a result, the transition to a radiation-dominated universe, i.e. reheating, occurs after fragmentation. We estimate the consequences on the production of gravitational waves by computing the contribution induced by the stiff equation-of-state era in addition to the signal generated by the fragmentation process for k = 4,6,8,10. We find that the signal generated during the fragmentation process gives a larger contribution than the one induced by the stiff equation-of-state era in given frequency ranges for all values of k. Our results are independent of the reheating temperature provided that reheating is achieved posterior to fragmentation. Our work shows that the dynamics of such weakly-coupled inflaton scenario can actually result in characteristic gravitational wave spectra with frequencies from Hz to GHz, in the reach of future gravitational wave observatories, in addition to the complementarity between upcoming detectors in discriminating (post)inflation scenarios. We advocate the need of developing high-frequency gravitational wave detectors to gain insight into the dynamics of inflation and reheating.

Cosmic inflation from fluctuating baby-Skyrme brane

In this work, we explore the inflationary dynamics induced by small fluctuations on the Skyrme brane, characterized by a time-dependent perturbative function ϕ̃. In the low-energy regime, the model successfully reproduces standard inflation, with a potential term dictated by the Skyrmion at the brane. Gravity localization is achieved at the brane, and the lowest energy scale is established at the asymptotic boundary. The model demonstrates the capability to emulate standard inflation dynamics, resembling ϕ̃4 potential characteristics under certain conditions. At higher energy regions, the behaviour of ϕ̃ is contingent upon the Skyrme term coupling constant λ, influencing reheating phases. The wave-like nature of fluctuations allows for energy transfer, resulting in a possibly lower reheating temperature. We also discuss the prospect of λ changing sign during inflation, presenting a non-standard coupling dependent on the matter field.

The James Webb Space Telescope (JWST) Anomalies Resolved

A model of the universe is offered that can derive the Hubble Constant independent of empirical measurement, using just a midline estimate of the age of the universe and simple arithmetic calculations. It can explain the JWST discoveries of apparent anomalous early galaxy formations without need of substantial revisions to established astrophysical theories, as the new findings have seemed to require. Concepts of “Dark energy”, cosmic flatness, cosmic inflation, and an accelerating expansion of the universe are rendered unnecessary or at least partly misinterpreted.

Impact of dark sector preheating on CMB observables

The prediction of a nearly scale-invariant spectrum of curvature and tensor fluctuations is among the main features of cosmic inflation. The current measurements of the primordial fluctuations in the cosmic microwave background (CMB) provide tight constraints on the amplitude of the scalar and tensor spectra, and the scalar tilt. However, the precise connection between these observables and a given inflationary model, depends on the expansion history between the end of inflation and the beginning of the radiation dominated era, which corresponds to the reheating epoch. This mapping between horizon exit and reentry of fluctuations, parametrized by the number of e-folds N*, can therefore be affected by the presence of a transient epoch of non-perturbative particle production during reheating (preheating). Using a combination of perturbative and lattice computations, we quantify the impact of preheating in a non-equilibrated dark matter sector on the CMB observables, under the assumption of a simultaneous perturbative decay of the inflaton into Standard Model particles. Combined with structure formation constraints, this allows us to impose stringent bounds on the post-inflationary reheating temperature.

Dissipative quintessential cosmic inflation

In this paper we construct a dissipative quintessential cosmic inflation. For this purpose, we add a multiplicative dissipative term in the standard quintessence field Lagrangian. We consider the specific form of dissipation as the time integral including the Hubble parameter and an arbitrary function that describes the dissipative properties of the quintessential scalar field. Inflation parameters and observables are calculated under slow-roll approximations and a detailed calculation of the cosmological perturbations is performed in this setup. We consider different forms of potentials and calculate the scalar spectral index and tensor-to-scalar ratio for a constant as well as variable dissipation function. To check the reliability of this model, a numerical analysis on the model parameters space is done in confrontation with recent observational data. By comparing the results with observational joint datasets at 68% and 95% confidence levels, we obtain some constraints on the model parameters space, specially the dissipation factor with e-folds numbers N=55 and N=60. As some specific results, we show that the power-law potential with a constant dissipation factor and N=60 is mildly consistent with observational data in some restricted domains of the model parameter space with very small and negative dissipation factor and a negligible tensor-to-scalar ratio. But this case with N=55 is consistent with observation considerably. For power-law potential and variable dissipation factor as Q=αϕn, the consistency with observation is also considerable with a reliable tensor-to-scalar ratio. The quadratic and quartic potentials with variable dissipation function as Q=αϕn are consistent with Planck2018 TT, TE, EE+lowE+lensing data at the 68% and 95% levels of confidence for some intervals of the parameter n.

Ward identities under the frame transformations in curved space-time

Scalar-tensor theories of gravity are considered to be competitors to Einstein's theory of general relativity for the description of classical gravity, as they are used to build feasible models for cosmic inflation. These theories can be formulated both in the Jordan and Einstein frame, which are related by a Weyl transformation with a field transformation, known together as a frame transformation. These theories formulated in the above two frames are often considered to be equivalent from the point of view of classical theory. However, this is no longer true from the quantum field theoretical perspective. In the present article, we show that the Ward identities derived in the above two frames are not connected through the frame transformation. This shows that the quantum field theories formulated in these two frames are not equivalent to each other. Moreover, this inequivalence is also shown by comparing the effective actions derived in these two frames.

Warm inflation triggered by entropies of some recent dark energy models within gravity

This manuscript aims to study cosmic warm inflation (WI) in the framework of - gravity, where Q represents the nonmetricity (NM) scalar. To accomplish this task, we introduce the Tsallis, Renyi, and Barrow holographic dark energy (HDE) entropies into the standard Friedmann equations. Utilizing the slow-roll (SR) approximation, we find exact analytic solutions for the inflaton field, the effective potential necessary to produce inflation, and the scale factor for both low- and high-dissipative regimes. We calculate key parameters, including SR parameters, the number of e-folds, the scalar spectral index and its running, and finally tensor-to-scalar ratio to assess the accuracy of the chosen DE models in light of the published observational data. The allowed ranges of the involved free parameters are found from the limits on inflationary observables imposed by the Planck data. It is concluded that the obtained results are consistent with proposed theoretical predictions up to the confidence level.

Connecting Cosmic Inflation to Particle Physics with LiteBIRD, CMB-S4, EUCLID, and SKA.

We show that next generation Cosmic Microwave Background (CMB) experiments will be capable of the first ever measurement of the inflaton coupling to other particles, opening a new window to probe the connection between cosmic inflation and particle physics. This sensitivity is based on the impact that the reheating phase after cosmic inflation has on the redshifting of cosmic perturbations. For our analysis we introduce a simple analytic method to estimate the sensitivity of future CMB observations to the reheating temperature and the inflaton coupling. Applying our method to LiteBIRD and CMB-S4 we find that, within a given model of inflation, these missions have the potential to impose both an upper and a lower bound on the inflaton coupling. Further improvement can be achieved if CMB data are combined with optical and 21cm surveys. Our results demonstrate the potential of future observations to constrain microphysical parameters that can provide an important clue to understand how a given model of inflation may be embedded in a more fundamental theory of nature.

A hybrid Euclidean–Lorentzian universe

The limited velocity in a geometry of Lorentzian signature seem to prevent the universe to reach thermodynamic equilibrium as suggested by the cosmic microwave background. Thus it was suggested that the universe which was initially minuscule has reached a more considerable radius in a short duration by a process known as cosmic inflation. However, to drive such a process have led to the suggestion of an ad-hoc scalar field the inflaton, which has no purpose in nature other than driving the cosmic inflation field and then stopping it once the universe reached the right size. In a recent paper it was shown that rapid expansion can occur without postulating an inflation by following Hawking’s suggestion and assuming that primordially the metric of the universe had an Euclidean signature, in which case velocity is not limited and thermalization and rapid expansion are derived without the need to assume an ad-hoc field. However, while in the previous work emphasis was put on the dynamics and physical statistics of the particles in a Euclidean space versus Lorentzian space in which both spaces were given. No mathematical model was given regarding the development of current Lorentzian space-time from the early Euclidean space-time, and how fundamental problems such as the space-time singularity and the homogeneity of the CMB can be solved in the hybrid Euclidean–Lorentzian picture. This lacuna is to be rectified in this paper.

Realisation of cosmic inflation under the purview of f(Q) gravity with agegraphic fluid

Realisation of cosmic inflation under the purview of f(Q) gravity with agegraphic fluid

Cosmic Inflation at the crossroads

The capability of Cosmic Inflation to explain the latest Cosmic Microwave Background and Baryonic Acoustic Oscillation data is assessed by performing Bayesian model comparison within the landscape of nearly three-hundred models of single-field slow-roll inflation. We present the first Bayesian data analysis based on the third-order slow-roll primordial power spectra. In particular, the fourth Hubble-flow function ε4 remains unbounded while the third function verifies, at two-sigma, ε3 ∈[-0.4,0.5], which is perfectly compatible with the slow-roll predictions for the running of the spectral index. We also observe some residual excess of B-modes within the BICEP/Keck data favoring, at a non-statistically significant level, non-vanishing primordial tensor modes: log(ε1) > -3.9, at 68% confidence level. Then, for 287 models of single-field inflation, we compute the Bayesian evidence, the Bayesian dimensionality and the marginalized posteriors of all the models' parameters, including the ones associated with the reheating era. The average information gain on the reheating parameter R reh reaches 1.3 ± 0.18 bits, which is more than a factor two improvement compared to the first Planck data release. As such, inflationary model predictions cannot meet data accuracy without specifying, or marginalizing over, the reheating kinematics. We also find that more than 40% of the scenarios are now strongly disfavored, which shows that the constraining power of cosmological data is winning against the increase of the number of proposed models. In addition, about 20% of all models have evidences within the most probable region and are all favored according to the Jeffreys' scale of Bayesian evidences.

A Comprehensive Overview of the Ulianov Theory

BThis article provides a comprehensive overview of the Ulianov Theory (UT), a pioneering model formulated by Dr. Policarpo Yoshin Ulianov. The UT offers a revolutionary approach to understanding the universe, anchored in mathematical rigor and logical scrutiny. Central to its framework is a redefined conception of time, positing it as a digital and complex variable time dimension and aligning the notion of imaginary time, with six digital spatial dimensions (three normal space dimensions an three spatial wrapped dimensions) named as General Octo-Dimension Universe (GODU), that also can see like four five-dimensions subuniverses separate by walls of space and walls of time, an original idea proposed by Issac Asimov in 1966 to explain a ”four leaf clover universe” beginning for noting, with the antimatter universes going to the negative time direction (travel to the past before the Big Bang). The Ulianov theory present a 12 basic particles model (6 particles and 6 antiparticles, like the quarks) seems as elastic holes in walls of time and space. The connections between it proposes particles properties (mass and electric charge) are familiar within our observable universe. In challenging prevailing scientific paradigms, UT beckons the scientific community to reassess foundational beliefs. The UT is based on only two fundamental forces (gravitational and eletromagnetic), replacing the Nuclear Strong add Week Forces by an Gravitational Contact Force, that becomes in play only wen two masses becomes in contact (with a Planck distance between then). Additionally, the article delves into a novel String Theory model (when photons, protons electrons and neutrons are basically the same length string, but wrapped in distinct ways). The UT also presents the ”Small Bang” hypothesis, suggesting the universe’s genesis from a small and cold space bubble (only a Planck length of diameter), with antimatter micro black hole becomes supermassive antimatter black holes and generating matter and antimatter (in the same proportion), stolen energy by the cosmic inflation field. Within the UT’s purview, seminal equations from classical physics, Einstein’s theories of relativity, and quantum mechanics are eloquently derived.

Why Does Inflation Look Single Field to Us?

Most high-energy constructions that realize a phase of cosmic inflation contain many degrees of freedom. Yet, cosmological observations are all consistent with single-field embeddings. We show how volume selection effects explain this apparent paradox. Because of quantum diffusion, different regions of space inflate by different amounts. In regions that inflate most, and eventually dominate the volume of the Universe, a generic mechanism is unveiled that diverts the inflationary dynamics towards single-field attractors. The formalism of constrained stochastic inflation is developed to this end.

Higgs Inflation in Unimodular Gravity

Abstract The discovery of the Higgs mechanism within the context of spontaneous symmetry breaking has offered a new perspective on early-time cosmic inflation and also on the relationship between elementary particles and dark energy, believed to drive the universe’s accelerating expansion. We suggest an inflation scenario driven by the Higgs boson within the framework of unimodular gravity, where the Higgs field acts as the inflaton and has a significant non-minimal coupling to the gravity. We present a detailed analysis of the problem in the Jordan and then Einstein frame for a unimodular Higgs inflation, followed by a comparison of our findings with the cosmic microwave background observations made by the Planck Collaboration and other joint data sets. Therefore, new constraints are imposed on the non-minimal coupling parameter, $\xi$, by determining the magnitudes required for effective cosmic inflation. We demonstrate that a substantial non-minimal coupling of order $\xi \sim 10^{2}\!-\!10^{4}$ is required for this model to match with the observed primordial spectrum.

Small Bang Model: A New Paradigm for Understanding Universe Creation

The Small Bang Model (SBM) introduces a revolutionary framework for the genesis of the universe, challenging conventional cosmological theories. By suggesting the universe originated from a zero-mass state, facilitated by antimatter black holes, the SBM provides fresh insights into galaxy formation and the distribution of matter and antimatter. This paper outlines the SBM’s foundational principles, contrasts it with the Big Bang theory, and highlights its potential to resolve longstanding cosmological puzzles. Notably, it presents empirical validations demonstrating distinct mass relationships between supermassive black holes and their host galaxies, supporting a novel classification into matter and antimatter galaxies. The Small Bang model is founded on two pivotal concepts: the theory of Cosmic Inflation and the principle of ‘Shunyata Universe’s Gene- sis’ (or ’Emptiness Universe’s Genesis’), a framework envisioning the universe’s inception as small, empty, and cold, entirely devoid of matter or energy. These SBM findings offer a groundbreaking perspective on the early universe’s dynamics and the distribution of cosmic matter, deepening our understanding of cosmic inflation. Consequently, we invite physicists to study, comprehend, and assess the new cosmological model proposed by the Small Bang Model.

Implementation and testing of a 100 mK ADR backed by a 4He/3He sorption fridge for CMB-S4 project

CMB-S4 is a ground-based experiment that will use large-format bolometer arrays to map Cosmic Microwave Background (CMB) polarization with unprecedented sensitivity, including the search for a B-mode polarization pattern associated with cosmic inflation. The focal planes on which the superconducting detectors are mounted weigh about 20 kg each and must be cooled at 100 mK. To reach this temperature for a first receiver fielding prototype hardware, we have developed an Adiabatic Demagnetization Refrigerator (ADR) used in conjunction with an existing 4He/3He sorption refrigerator.The ADR unit described here is based on a Chromium Potassium Alum (CPA) salt pill. It is backed by a 3-stage (4He/3He/3He) sorption fridge, coupled through a 3He gas-gap heat switch. This heat switch is connected to a 3He stage of the sorption fridge to dissipate the heat generated by magnetization. The ADR is cycled with a 1.3 T magnetic field. The parasitic field at the detectors’ location during observations is kept below 2.5 µT thanks to a ferromagnetic shield. The pill is supported by Kevlar lines, which are doubly intercepted by the 4He and 3He stages of the sorption fridge to reduce conductive heat losses. With a total recycling time of 12 hours, this cryogenic assembly provides 2 µW of cooling power during 48 hours at 100 mK. The ADR has been designed by CEA/DSBT in France and is now implemented in a cryostat at Caltech.

Results and forecasts on cosmic inflation from weak lensing

Results and forecasts on cosmic inflation from weak lensing