Inflationary Models Research Articles

A Community Initiative to Increase Colorectal Cancer Knowledge, Awareness, and Intent to Screen in an Underserved Region.

Background: Colorectal cancer (CRC) is a leading cause of cancer-related deaths in the United States despite the availability of effective preventive screening. Objective: This project was designed as a community awareness initiative to increase CRC awareness, knowledge, and intent to discuss and complete CRC screening. Methodology: This quasi-experimental study had a QI focus and used a convenience sample in a public setting assessing CRC awareness, knowledge, and intent to discuss and complete screening after participating in an inflatable colon tour. Results: CRC awareness and knowledge scores showed a statistically significant increase in posttest scores at p < .001. Posttour, there was an 82% and 133% increase in people who identified as "very likely" or "definitely" willing to discuss CRC with their healthcare provider and complete CRC screening within the next 6 months, respectively. Conclusions: In line with previous studies, the inflatable colon model was a successful means of increasing CRC knowledge, awareness, and intent to complete CRC screening. Implications for Nursing: This project is evidence that community events can successfully increase knowledge in underserved populations. Implementing community-based interactive education, such as an inflatable colon tour, is an effective way to incorporate evidence-based education for vulnerable populations.

Embedding warm natural inflation in f(ϕ)T gravity

We study warm inflation in the framework of [Formula: see text] gravity, where [Formula: see text] is the inflaton and T is the trace of the energy–momentum tensor. The inflaton field is assumed to roll on the natural inflaton potential and the result is analyzed in light of Planck 2018 and BICEP/Keck 2021 data. We start by obtaining the field equations under slow-roll approximations. The scalar and tensor power spectra and their corresponding spectral index and tensor-to-scalar ratio with a temperature-dependent form of the dissipation coefficient during the inflationary era are then evaluated. It is found that the warm inflation model in [Formula: see text] gravity is compatible with observational bands.

New models of quintessential inflation featuring plateau and hilltop potentials

We introduce a new class of hilltop and plateau potentials which can successfully unify inflation and dark energy resulting in quintessential inflation (QI). Interestingly these new potentials are related through an inverse transformation. Namely, if V(ϕ)=V0v(ϕ) is a plateau potential then the inverse potential V(ϕ)=V0v(ϕ)-1 describes hilltop QI. A simple example is provided by the KKLT-inspired potential v(ϕ)=M2n+ϕ2nN2n+ϕ2n. When M/N≪1 this potential describes plateau QI, while its inverse, v(ϕ)-1 describes hilltop QI. Other simple models of QI arise for the class of potentials V(ϕ)∼exp∓f(ϕ), where the − (+) sign is associated with a plateau (hilltop). A key feature of this new class of QI models is the near absence of small dimensionless parameters, or small mass parameters (relative to the energy scale of the Standard Model of particle physics) – which are usually associated with the presence of dark energy. A forecast for the gravitational wave background generated in these models is provided.

A new approach in classical Klein-Gordon cosmology: “Small Bangs”, inflation and Dark Energy

Abstract In this work, we analyze the cosmological model in which the expansion is driven by a classical, free Klein-Gordon field on a flat, four-dimensional Friedmann-Lemaitre-Robertson-Walker spacetime. The model allows for arbitrary mass, non-zero cosmological constant and coupling to curvature. We find that there are strong restrictions to the parameter space, due to the requirement for the reality of the field values. At early cosmological times, we observe Big Bang singularities, solutions where the scale factor asymptotically approaches zero, and Small Bangs. The latter are solutions for which the Hubble parameter diverges at a finite value of the scale factor. They appear generically in our model for certain curvature couplings. An early inflationary era is observed for a specific value of the curvature coupling without further assumptions (unlike in many other inflationary models). A late-time Dark Energy period is present for all solutions with positive cosmological constant, numerically suggesting that a “cosmic no-hair” theorem holds under more general assumptions than the original Wald version which relies on classical energy conditions. The classical fields in consideration can be viewed as resembling one-point functions of a semiclassical model, in which the cosmological expansion is driven by a quantum field.&amp;#xD;

Chasing cosmic inflation: constraints for inflationary models and reheating insights

We investigate the impact of different choice of prior's range for the reheating epoch on cosmic inflation parameter inferencein light of cosmic microwave background (CMB) anisotropy measurements from the Planck 2018 legacy releasein combination with BICEP/Keck Array 2018 data and additional late-time cosmological observations such as uncalibratedType Ia supernovae from the Pantheon catalogue, baryon acoustic oscillations and redshift space distortionsfrom SDSS/BOSS/eBOSS.Here, we explore in particular the implications for the combination of reheating and inflationary-model parameter spaceconsidering R+R 2 inflation and a broad class of α-attractor and D-brane models.Propagating the uncertainties due to an unknown reheating phase, these inflationary models completely cover the n s-r parameter space allowed by Planck and BICEP/Keck dataand represent good targets for future CMB and large-scale structure experiments.We perform a Bayesian model comparison of inflationary models, taking into account the reheating uncertaintiesassuming a conservative but accurate modelling of inflationary predictions.R+R 2 inflation, T-model α-attractor inflation for n=1, E-model α-attractor inflation for n=1/2,and KKLT inflation for p=5 are the better performing models, with none being preferred at a statistically significant level.

Robustness of inflation to kinetic inhomogeneities

We investigate the effects of large inhomogeneities in both the inflaton field and its momentum. We find that in general, large kinetic perturbations reduce the number of e-folds of inflation. In particular, we observe that inflationary models with sub-Planckian characteristic scales are not robust even to kinetic energy densities that are sub-dominant to the potential energy density, unless the initial field configuration is sufficiently far from the minimum. This strengthens the results of our previous work. In inflationary models with super-Planckian characteristic scales, despite a reduction in the number of e-folds, inflation is robust even when the potential energy density is initially sub-dominant. For the cases we study, the robustness of inflation strongly depends on whether the inflaton field is driven into the reheating phase by the inhomogeneous scalar dynamics.

SIMP dark matter during reheating

Strongly interacting massive particle (SIMP) has become one of the promising dark matter (DM) candidates due to its capability of addressing the small-scale anomaly, where the final DM abundance is set via the freeze-out of 3→ 2 or 4→ 2 annihilation process involving solely the dark sector particles. In this work, we explore the freeze-out of SIMP DM during the inflationary reheating epoch. During reheating, the radiation energy density evolves differently based on the shape of inflaton potential and spin of its decay products than the standard radiation-dominated picture; as a result, in this scenario, the freeze-out temperature varies distinctly with DM mass compared to the standard case. Large entropy injection due to inflaton decay demands a smaller cross-section to satisfy the observed relic than the standard radiation-dominated freeze-out case. The required cross-section, satisfying the relic density constraint and the maximum allowed thermally averaged cross-section by the unitarity of the S-matrix, set an upper limit on the DM mass. The upper bound on the mass of the dark matter for 3→2 (4→2) is 1 GeV (7 MeV), assuming a radiation-dominated background. Interstingly, these limits get relaxed to 106 (104) GeV for 3→2 (4→2) SIMP dark matter for quadratic inflaton potential. We find that a small amount of DM parameter space survives for reheating with quadratic inflaton potential after considering the lower bound of reheating temperature, put by the latest CMB observation depending on the inflationary models. In the case of the quartic inflaton potential, the allowed DM parameter space gets reduced compared to the quadratic case.

Warm affine inflation

The warm inflationary scenario is investigated in the context of affine gravity formalism. A general framework is provided for studying different single-field potentials. Using the sphaleron mechanism we explain the continuous dissipation of the inflaton field into radiation, leading to the Γ = Γ0 T 3 dissipation coefficient. The treatment is performed in the weak and strong dissipation limits. We consider the quartic potential as a case study to provide a detailed study. Moreover, in this study, we discuss various constraints on inflationary models in general. We compare the theoretical results of the quartic potential model within warm inflation with the observational constraints from Planck 2018 and BICEP/Keck 2018, as presented by the tensor-to-scalar ratio, spectral index and the perturbation spectrum.

Constraining primordial non-Gaussianity with Density-Split Clustering

Obtaining tight constraints on primordial non-Gaussianity (PNG) is a key step in discriminating between different models for cosmic inflation. The constraining power from large-scale structure (LSS) measurements is expected to overtake that from cosmic microwave background (CMB) anisotropies with the next generation of galaxy surveys including the Dark Energy Spectroscopic Instrument (DESI) and Euclid. We consider whether Density-Split Clustering (DSC) can help improve PNG constraints from these surveys for local, equilateral and orthogonal types. DSC separates a surveyed volume into regions based on local density and measures the clustering statistics within each environment. Using the Quijote simulations and the Fisher information formalism, we compare PNG constraints from the standard halo power spectrum, DSC power spectra and joint halo/DSC power spectra. We find that the joint halo/DSC power spectra outperform the halo power spectrum by factors of ∼ 1.4, 8.8, and 3.6 for local, equilateral and orthogonal PNG, respectively. This is driven by the higher-order information that DSC captures on small scales. We find that applying DSC to a halo field does not allow sample variance cancellation on large scales by providing multiple tracers of the same volume with different local PNG responses. Additionally, we introduce a Fourier space analysis for DSC and study the impact of several modifications to the pipeline, such as varying the smoothing radius and the number of density environments and replacing random query positions with lattice points.

Analytic results in aligned axion inflation

The original model of axion natural inflation produces a tensor-to-scalar ratio above the experimental limit. Aligned axion inflation admits inflationary trajectories that originate near a saddle point of the two-field potential, and terminate due to the instability of the orthogonal direction. The phenomenology of these solutions is within the current constraints, and a range of parameters will be probed by the next stage CMB experiments. We provide the analytic solution for these trajectories and very compact analytic expressions for the associated phenomenology. For parameters leading to the observed value for the scalar spectral tilt the extension of the inflationary trajectory is sub-Planckian. However, one eigenvalue of the axion kinetic matrix (in the basis that diagonalizes the potential) is trans-Planckian. Finally, we discuss the post-inflationary evolution after the instability. In some cases, the fields reach a second inflationary valley, connected to a minimum. Multiple stages of inflation might be a more general occurrence in multiple-field inflationary models with trajectories starting next to critical points.

Primordial black holes in SB SUSY Gauss-Bonnet inflation

Here, we explore the formation of primordial black holes (PBHs) within a scalar field inflationary model coupled to the Gauss-Bonnet (GB) term, incorporating the low-scale spontaneously broken supersymmetric (SB SUSY) potential.The coupling function amplifies the curvature perturbations, consequently leading to the formation of PBHs and detectable secondary gravitational waves (GWs).Through the adjustment of the model parameters, the inflaton can be decelerated during an ultra-slow-roll (USR) phase, thereby augmenting curvature perturbations. Beside the observational constraints, the swampland criteria are investigated.Our computations forecast the formation of PBHs with masses around 𝒪(10)M ⊙, aligning with the observational data of LIGO-Virgo, and PBHs with masses 𝒪(10-6)M ⊙ as potential explanation for the ultrashort-timescale microlensing events recorded in the OGLE data.Additionally, our proposed mechanism can generate PBHs with masses around 𝒪(10-13)M ⊙, constituting roughly 99% of the dark matter.The density parameters of the produced GWs (ΩGW 0) intersect with the sensitivity curves of GW detectors. Two cases of our model fall within the nano-Hz frequency regime. One of them satisfies the power-law scaling as ΩGW(f) ∼ f 5-γ, with the γ = 3.51, which is consistent with the data of NANOGrav 15-year.

Large field polynomial inflation in Palatini f(R,ϕ) gravity

In this paper, we employ the Palatini formalism to investigate the dynamics of large-field inflation using a renormalizable polynomial inflaton potential in the context of f(R,ϕ) gravity. Assuming instant reheating, we make a comparative analysis of large-field polynomial inflation (PI). We first consider the minimal and non-minimal coupling of inflaton in R gravity, and then we continue with the minimally and non-minimally coupled inflaton in f(R,ϕ) gravity. We scan the parameter space for the inflationary predictions (n s and r) consistent with the Planck and BICEP/Keck 2018 results as well as the sensitivity forecast of the future CMB-S4 and depict the compliant regions in the ϕ 0-β plane where ϕ 0 and β are two parameters of polynomial inflation model which control the saddle point of the potential and the flatness in the vicinity of this point respectively. We find that a substantial portion of the parameter space aligns with the observational data.

Some general points for inflation models

Some general points for inflation models

Induced gravitational waves, metastable cosmic strings and primordial black holes in GUTs

We explore the cosmological and astrophysical implications of a realistic hybrid inflation model based on flipped SU(5). The model contains superheavy metastable cosmic strings arising from a waterfall field that encounters a limited number of e-foldings during the inflationary phase. In addition to the gravitational waves emitted by the metastable strings, there also appear scalar induced gravitational waves linked to the waterfall phase transition. These two independent sources of gravitational waves can yield a combined spectrum that is compatible with the recent PTA measurements, and with additional features that can be probed in future experiments. We also show the appearance of primordial black holes with mass on the order of 1029 g from the waterfall phase transition, and with an abundance that can be tested in the gravitational lensing experiments.

Two-Loop Corrections in Power Spectrum in Models of Inflation with Primordial Black Hole Formation

Two-Loop Corrections in Power Spectrum in Models of Inflation with Primordial Black Hole Formation

Inflation models with Peccei–Quinn symmetry and axion kinetic misalignment

We propose a consistent framework with the U(1) Peccei–Quinn (PQ) symmetry for obtaining the initial condition for axion kinetic misalignment from inflation. We introduce a PQ complex scalar field and an extra Higgs doublet, which are conformally coupled to gravity, and three right-handed neutrinos for the seesaw mechanism. In the DFSZ type scenarios for the axion, we obtain the PQ anomalies from the Standard Model quarks carrying nonzero PQ charges in some of two Higgs doublet models, solving the strong CP problem by the QCD potential for the axion. Assuming that the PQ symmetry is explicitly violated in the scalar potential by quantum gravity effects, we show that a sufficiently large initial axion velocity can be obtained before the QCD phase transition while avoiding the axion quality problem. As inflation is driven by the radial distance from the origin in the space of scalar fields close to the pole of the kinetic terms in the Einstein frame, we obtain successful inflationary predictions and set the initial axion velocity at the end of inflation. Focusing on the pure PQ inflation with a small running quartic coupling for the PQ field, we discuss the post-inflationary dynamics for the inflaton and the axion. As a result, we show that a sufficiently high reheating temperature can be obtained dominantly from the Higgs-portal couplings to the PQ field, while being consistent with axion kinetic misalignment, the stability for the Higgs fields during inflation and the non-restoration of the PQ symmetry after reheating.

STOLAS: STOchastic LAttice Simulation of cosmic inflation

We develop a C++ package of the STOchastic LAttice Simulation (STOLAS) of cosmic inflation. It performs the numerical lattice simulation in the application of the stochastic-δ N formalism. STOLAS can directly compute the three-dimensional map of the observable curvature perturbation without estimating its statistical properties. In its application to two toy models of inflation, chaotic inflation and Starobinsky's linear-potential inflation, we confirm that STOLAS is well-consistent with the standard perturbation theory. Furthermore, by introducing the importance sampling technique, we have success in numerically sampling the current abundance of primordial black holes (PBHs) in a non-perturbative way. The package is available at https://github.com/STOchasticLAtticeSimulation/STOLAS_dist.

Open EFT treatment of inflation with thermal initial conditions

Investigating the thermal inflationary model, we introduce stochastic effects, incorporating a cutoff parameter σ which distinguishes between quantum and classical modes. Testing the model against Planck 2018 data, we observe a preference for a non-zero σ at least at 68% C.L., suggesting the classicalization of most modes and providing a theoretical foundation for the quantum to classical transition. As a result of introducing the stochastic effects, we find that the solution to the large-scale power deficit requires a lower comoving temperature of inflaton.

CMB constraints on natural inflation with gauge field production

The natural inflation model with a periodic cosine potential is ruled out by recent Planck 2018 data for the decay constant f ≲ 5.5 M Pl. If the Planck data is combined with the BICEP Keck array and BAO data, the model is excluded (at 2-σ) for all values of f. In this context, we revisit the model when the pseudoscalar inflation ϕ is coupled with a gauge field via a coupling of the form α/fϕ FF̃, where F(F̃) denotes the gauge field (dual) strength tensor, and α is the coupling constant. The back-reactions associated with the gauge field production during the later stages of inflation extend the duration of inflation. We numerically evaluate the dynamics of the fields while neglecting the effects due to the perturbations in the inflaton field. It allows us to determine the scalar and tensor power spectra leading to the calculations of observables at the Cosmic Microwave Background (CMB) scales. We find that the natural inflation model survives the test of the latest data only for a certain range of the coupling constant α. Our analysis shows that the latest constraints coming from the scalar spectral index are more stringent than the ones arising from the non-gaussianities and the running of the scalar spectrum. This leads to lower and upper bounds on ξ *, the parameter that controls the growth of the gauge field.

Inflation Targeting with an Optimal Nonlinear Monetary Rule—The Case Study of Colombia

This article examines whether Banco de la República (Banrep), Colombia’s central bank, has operated under a dual-regime policy framework—one for recessionary periods and another for periods of economic overheating—since adopting inflation targeting (IT) from Q4 2000 to Q4 2019. We modify the canonical New Keynesian inflation model to accommodate an optimal nonlinear monetary rule aligned with a two-regime policy framework. Using a LSTAR model estimated over the study period, with the output gap lagged by three periods as the transition variable, we identify two distinct monetary regimes. Our findings reveal that the smooth transitions between regimes were driven by shifts in Banrep’s preferences related to its loss function, alongside adjustments in the parameters of the aggregate demand and supply curves within the Colombian economy. Notably, we observe that a modified Taylor principle is not met in either identified monetary regime. This suggests that, in this context, IT has been a successful policy framework even without requiring the policy interest rate to respond aggressively to inflation gaps, as the Taylor principle would otherwise dictate.