arXiv subjects

Zygmunt Lalak

Publications and source records attributed to Zygmunt Lalak.

At least 19 recordsLinked to original sources

arXiv2026

Induced Multi-phase Inflation with Reheating: Leptogenesis and Dark Matter Production in Metric versus Palatini

We study non-minimally coupled scalar-induced multi-phase inflation in metric and Palatini gravity, considering linear, Brans-Dicke-like, and Higgs-like sectors. The scalar spectral index lies in the range $ n_s \simeq 0.93 \ \text{--} \ 0.98 $, consistent with \textit{Planck} and combined \textit{Planck}+ACT data. The tensor-to-scalar ratio can reach $ r \sim 0.03 $ in metric, whereas Palatini models generically predict $ r \lesssim 10^{-5} $. In the Palatini case, field excursions remain sub-Planckian, and the perturbative unitarity cutoff is raised. Reheating proceeds via perturbative inflaton decays into Higgs bosons and fermionic dark matter (DM) through the portal coupling $ λ_{12} $ and Yukawa coupling $ y_χ$. Radiative stability of the inflationary plateau constrains the couplings to $ y_χ, λ_{12} \sim 10^{-7} \ \text{--} \ 10^{-3} $, implying $ 4\,\mathrm{MeV} \lesssim T_{\rm rh} \lesssim 10^{15}\,\mathrm{GeV} $. Palatini realizations require smaller couplings and thus a narrower reheating window. Non-thermal DM production $χ$ from inflaton decays is viable for DM mass $ m_χ\sim \mathrm{keV} \ \text{--} \ \mathrm{PeV} $ with $ y_χ\lesssim 10^{-6} $ over large parameter regions. We estimate the inflaton-right-handed neutrino (RHN) Yukawa coupling $ y_N $ required for successful baryogenesis via non-thermal leptogenesis within a Type-I seesaw framework, for the lightest RHN mass $ M_{N_1} \sim 10^{9} \ \text{--} \ 10^{14}\,\mathrm{GeV} $, provided $ M_{N_1} > T_{\rm max} $, where $ T_{\rm max} $ follows from radiatively consistent reheating. In Palatini scenarios, the lower maximal temperature and tighter stability bounds further restrict the leptogenesis parameter space.

hep-ph↗

arXiv2025

Post-inflationary production of particle Dark Matter: non-minimal Natural and Coleman--Weinberg inflationary scenarios

We investigate the production of non-thermal fermionic dark matter particles during the reheating era following slow roll inflation, driven by inflaton $φ$ non-minimally coupled to the curvature scalar, $\mathcal{R}$. Two types of non-minimal couplings are considered: $ξφ^2\cal{R}$ for both natural (referred to as NM-N) and for Coleman-Weinberg (referred to as NM-CW) inflation, and $α\left(1+\cos(\fracφ{f_a})\right)$ only for natural inflation (referred to as NMP-N), where $α$ and $ξ$ are dimensionless parameters and $f_a$ is an energy scale. We determine benchmark values for slow roll inflationary scenarios satisfying current bounds from Cosmic Microwave Background (CMB) radiation measurement and find the mass of inflaton to be $m_ϕ\sim {\cal O}\left(10^{12}\right) \text{GeV}$ for all three inflationary scenarios and tensor-to-scalar ratio, $r\sim 0.0177$ (for NM-N), $\sim 0.0097$ (for NMP-N), and $r\sim 0.0157$ (for NM-CW) which fall inside $1-σ$ contour on scalar spectral index versus $r$ plane of Planck2018+BICEP3+KeckArray2018 joint analysis, and can be probed by future CMN~observations e.g. Simons Observatory. We then show that dark matter particles produced from the decay of inflaton can fully match the present-day cold dark matter (CDM) yield, as well as other cosmological constraints, if the coupling value between inflaton and dark matter, $y_χ$, and the dark matter mass, $m_χ$, are within the range $10^{-1}\gtrsim y_χ\gtrsim 10^{-20}$ for NM-N and NMP-N ($10^{-4}\gtrsim y_χ\gtrsim 10^{-20}$ for NM-CW) and ${\cal O}\left(\text{keV}\right)\lesssim m_χ\lesssim m_ϕ/2$ (for NM-N, NMP-N, and NM-CW). The exact range of $y_χ$ and $m_χ$ varies with different benchmark values as well as parameters of inflation, like energy scale of inflation and $r$, some of which are within reach of next-generation CMB experiments.

hep-ph↗

arXiv2024

Post-inflationary Leptogenesis and Dark Matter production: Metric versus Palatini formalism

We investigate production of non-thermal dark matter particles and heavy sterile neutrinos from inflaton during the reheating era, which is preceded by a slow-roll inflationary epoch with a quartic potential and non-minimal coupling ($ξ$) between inflaton and gravity. We compare our analysis between metric and Palatini formalism. For the latter, the tensor-to-scalar ratio, r, decreases with $ξ$. We find that for $ξ=0.5$ and number of $e$-folds $\sim 60$, $r$ can be as small as $\sim {\cal O}\left(10^{-3}\right)$ which may be validated at future reaches of upcoming CMB observation such as CMB-S4 etc. We identify the permissible range of Yukawa coupling $y_χ$ between inflaton and fermionic DM $χ$, to be ${\cal O}\left(10^{-3.5}\right)\gtrsim y_χ\gtrsim {\cal O}\left(10^{-20}\right)$ for metric formalism and ${\cal O}\left(10^{-4}\right)\gtrsim y_χ\gtrsim {\cal O}\left(10^{-11}\right)$ for Palatini formalism which is consistent with current PLANCK data and also within the reach of future CMB experiments. For the scenario of leptogenesis via the decay of sterile neutrinos produced from inflaton decay, we also investigate the parameter space involving heavy neutrino mass $M_{N_1}$ and Yukawa coupling $y_{N_1}$ of sterile neutrino with inflaton, which are consistent with current CMB data and successful generation of the observed baryon asymmetry of the universe via leptogenesis. In contrast to metric formalism, in the case of Palatini formalism, for successful leptogenesis to occur, we find that $y_{N_1}$ has a very narrow allowable range and is severely constrained from the consistency with CMB predictions.

astro-ph.CO↗

arXiv2024

Post-inflationary production of particle Dark Matter: Hilltop and Coleman-Weinberg inflation

We investigate the production of non-thermal dark matter (DM), $χ$, during post-inflationary reheating era. For inflation, we consider two slow roll single field inflationary scenarios - generalized version of Hilltop (GH) inflation, and Coleman-Weinberg (CW) inflation. Using a set of benchmark values that comply with the current constraints from Cosmic Microwave Background Radiation (CMBR) data for each inflationary model, we explored the parameter space involving mass of dark matter particles, $m_χ$, and coupling between inflaton and $χ$, $y_χ$. For these benchmarks, we find that tensor-to-scalar ratio $r$ can be as small as $2.69\times 10^{-6}$ for GH and $1.91\times 10^{-3}$ for CW inflation, both well inside $1-σ$ contour on scalar spectral index versus $r$ plane from Planck2018+BICEP3+KeckArray2018 dataset, and testable by future cosmic microwave background (CMB) observations e.g. Simons Observatory. For the production of $χ$ from the inflaton decay satisfying CMB and other cosmological bounds and successfully explaining total cold dark matter density of the present universe, we find that $y_χ$ should be within this range ${\cal O}\left(10^{-4}\right) \gtrsim y_χ\gtrsim {\cal O}\left(10^{-20}\right)$ for both inflationary scenarios. We also show that, even for the same inflationary scenario, the allowed parameter space on reheating temperature versus $m_χ$ plane alters with inflationary parameters including scalar spectral index, $r$, and energy scale of inflation.

hep-ph↗

arXiv2023

Measuring inflaton couplings via dark radiation as $ΔN_{\rm eff}$ in CMB

We study the production of a beyond the Standard Model (BSM) free-streaming relativistic particles which contribute to $N_{eff}$ and investigate how much the predictions for the inflationary analysis change. We consider inflaton decay as the source of this dark radiation (DR) and use the Cosmic Microwave Background (CMB) data from $\textit{Planck}$-2018 to constrain the scenarios and identify the parameter space involving couplings and masses of the inflaton that will be within the reach of next-generation CMB experiments like SPT-3G, CMB-S4, $\text{CMB-Bh$\overline{a}$rat}$, PICO, CMB-HD, etc. We find that if the BSM particle is produced only from the interaction with inflaton along with Standard Model (SM) relativistic particles, then its contribution to $N_{eff}$ is a monotonically increasing function of the branching fraction, $B_X$ of the inflaton to the BSM particle $X$; $\textit{Planck}$ bound on $N_{eff}$ rules out such $B_X \gtrsim 0.09$. Considering two different analyses of $\textit{Planck}$+BICEP data together with other cosmological observations, $N_{eff}$ is treated as a free parameter, which relaxes the constraints on scalar spectral index ($n_s$) and tensor-to-scalar ratio ($r$). The first analysis leads to predictions on the inflationary models like Hilltop inflation being consistent with the data. Second analysis rules out the possibility that BSM particle $X$ producing from the inflaton decay in Coleman-Weinberg Inflation or Starobinsky Inflation scenarios. To this end, we assume that SM Higgs is produced along with the BSM particle. We explore the possibilities that $X$ can be either a scalar or a fermion or a gauge boson and consider possible interactions with inflaton and find out the permissible range on the allowed parameter space Planck and those which will be within the reaches of future CMB observations.

hep-ph↗

arXiv2023

Growth of curvature perturbations for PBH formation \& detectable GWs in non-minimal curvaton scenario revisited

We revisit the growth of curvature perturbations in non-minimal curvaton scenario with a non-trivial field metric $λ(ϕ)$ where $ϕ$ is an inflaton field, and incorporate the effect from the non-uniform onset of curvaton's oscillation in terms of an axion-like potential. The field metric $λ(ϕ)$ plays a central role in the enhancement of curvaton field perturbation $δχ$, serving as an effective friction term which can be either positive or negative, depending on the first derivative $λ_{,ϕ}$.Our analysis reveals that $δχ$ undergoes the superhorizon growth when the condition $η_\text{eff} \equiv - 2 \sqrt{2ε} M_\text{Pl} { λ_{,ϕ} \over λ} < -3$ is satisfied. This is analogous to the mechanism responsible for the amplification of curvature perturbations in the context of ultra-slow-roll inflation, namely the growing modes dominate curvature perturbations. As a case study, we examine the impact of a Gaussian dip in $λ(ϕ)$ and conduct a thorough investigation of both the analytical and numerical aspects of the inflationary dynamics.Our findings indicate that the enhancement of curvaton perturbations during inflation is not solely determined by the depth of the dip in $λ(ϕ)$. Rather, the first derivative $λ_{,ϕ}$ also plays a significant role, a feature that has not been previously highlighted in the literature. Utilizing the $δ\mathcal{N}$ formalism, we derive analytical expressions for both the final curvature power spectrum and the non-linear parameter $f_\text{NL}$ in terms of an axion-like curvaton's potential leading to the non-uniform curvaton's oscillation. Additionally, the resulting primordial black hole abundance and scalar-induced gravitational waves are calculated, which provide observational windows for PBHs.

astro-ph.CO↗

arXiv2023

Spontaneous scale symmetry breaking at high temperature

We consider a scale symmetric extension of the Standard Model Higgs scalar sector. The new sector, dilaton, is responsible for the generation of mass scales and may have geometric origin in the Weyl gravity $\tilde{R}^2$ term. We show how temperature as a mass scale breaks scale symmetry explicitly and through a nonvanishing thermal vev. In addition we demonstrate that cosmological evolution of the dilaton-Higgs system can lead to late time mass scales, which agree with the Standard Model.

hep-ph↗

arXiv2022

Stability of domain walls in models with asymmetric potentials

We study the evolution of cosmological domain walls in models with asymmetric potentials. Our research goes beyond the standard case of spontaneous breaking of an approximate symmetry. When the symmetry is explicitly broken the potential exhibits nearly degenerate minima which can lead to creation of a metastable network of domain walls. The time after which the network will decay depends on the difference of values of the potential in minima, its asymmetry around the maximum separating minima and the bias of the initial distribution of the field. Effect of asymmetry around the maximum separating minima is novel one that we study with a new type of potential. Using numerical lattice simulations we determine relative importance of these factors on decay time of networks for generic potentials. We find that even very small departures from the symmetric initial distribution case lead to rapid decay of the domain wall network. As a result creation of a long lasting network capable of producing observable gravitational wave signals is much more difficult than previously thought. On the other hand details of the shape of the potential turn out to be much less important than was expected and the evolution of network from symmetric distribution is controlled by the difference of values of the potential in the minima.

astro-ph.CO↗

arXiv2021

Primordial black holes as dark matter and gravitational waves from bumpy axion inflation

We consider a mechanism for producing a significant population of primordial black holes (PBHs) and an observable stochastic gravitational wave background (SGWB) within string theory inspired models of inflation. In this framework where inflaton is identified as a non-compact axion-like field, sub-leading non-perturbative effects can superimpose steep cliffs connected by smooth plateaus onto the underlying axion potential. In the presence of coupling to Abelian gauge fields, the motion of axion on the cliff-like region(s) of its potential triggers a localized production of one helicity state of gauge fields due to the temporary fast-roll of axion around such a feature. In this setup, primordial fluctuations sourced by vector fields exhibit a localized peak in momentum space corresponding to modes that exit the horizon when the axion velocity is maximal. As an application of this general mechanism, we present an example of axion inflation which both matches Planck observations at CMB scales and generates a population of light PBHs ($M_{\rm PBH} \simeq 10^{-13} M_{\odot}$) that can account for all dark matter. In this scenario, the enhanced scalar fluctuations that leads to PBHs also generate an observable SGWB of induced origin at LISA scales. The amplitude and shape of the resulting GW signal inherits specific properties (such as non-Gaussianity and its shape) of its scalar sources that may allow us to distinguish this mechanism from other inflationary scenarios and astrophysical backgrounds. This GW signal together with an observation of PBH distribution at the corresponding scales can thus provide a window to the inflationary dynamics on scales much smaller than those probed by Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) Measurements.

astro-ph.CO↗

arXiv2020

Two interacting scalars system in curved spacetime -- vacuum stability from the curved spacetime Effective Field Theory (cEFT) perspective

In this article we investigated the influence of the gravity induced higher dimensional operators on the issue of vacuum stability in a model containing two interacting scalar fields. As a framework we used the curved spacetime Effective Field Theory (cEFT) applied to the aforementioned system in which one of the scalars is heavy. After integrating out the heavy scalar we used the standard Euclidean approach to the obtained cEFT. Apart from analyzing the influence of standard operators like the non-minimal coupling to gravity and the dimension six contribution to the scalar field potential, we also investigated the rarely discussed dimension six contribution to the kinetic term and the new gravity induced contribution to the scalar quartic self-interaction.

hep-th↗

arXiv2020

Novel matter coupling in Einstein gravity

A general framework of the novel matter coupling in the Einstein gravity is introduced. We firstly prove that a class of theories whose Hamiltonian constraint is given by an arbitrary function $f(H_g)$, where $H_g$ is the Hamiltonian constraint of general relativity (GR), is equivalent to GR in the vaccum. A novel Jordan frame is defined when GR is rewritte in terms of one of its equivalents in this class. The transformation between the novel Jordan frame and the Eintein frame is a redifinition of lapse. We discuss two types of consistency condition for matter to couple to Einstein gravity in the novel Jordan frame. The Type I consistency condition is found by demanding all constraints to be first class; the type II consistency condition is found by demanding the algebra is closed when matter minimally couples to gravity in the novel Jordan frame, which an additional gauge condition is required. We discuss the cosmological implications from these two types of matter coupling.

gr-qc↗

arXiv2019

Higgs domain walls in the thermal background

Most cosmological models predict that the universe was hot and dense at the early stages of it's evolution. In this paper we analyse the influence of the thermal bath of Standard Model particles on the dynamics of cosmological Higgs domain walls. This manuscript poses an~extension of our earlier work in which we investigated the evolution of networks of Higgs domain walls neglecting the impact of temperature variation. Using the thermally corrected effective potential of Standard Model we have found that both the position of the local maximum $h_{max}$ separating minima and the width of domain walls strongly depend on temperature $T$. For temperatures higher than $10^{10}\; \textrm{GeV}$ they respectively increase proportionally and decrease inverse proportionally to the increasing temperature. Thus, the energy scale of the problem follows the value of temperature. Our numerical lattice simulations based on the PRS algorithm reveal that Higgs domain walls in the presence of the background thermal bath are highly unstable and decay shortly after formation. Moreover we have found that the fraction of horizons produced by inflation in which Higgs field expectation value is higher then $h_{max}$ needs to be very low in order for the evolution of the~network of the domain walls to end in the electroweak vacuum. This means that Higgs domain walls necessarily were very rare objects and their average energy density was very small. As a result, the domain walls can not significantly effect cosmological observables.

hep-ph↗

arXiv2018

Vanishing trace anomaly in flat spacetime

Quantum scale invariant regularization is a variant of dimensional regularization where the renormalization scale is treated as a dynamical field. But, rather than be regarded as a novel regularization method on par with dimensional regularization, momentum cutoff, Pauli-Villars etc., it should be understood as a way to define a subset in the infinite space of nonrenormalizable models of certain type. The subset realizes the demand that renormalization scale, along with any other dimensionful parameters, should be interpreted as a dynamical field's homogeneous background. This restriction is most straightforwardly implemented using dimensional regularization but it can hypothetically be imposed with any regularization method. Theories that satisfy it offer a new perspective on the radiative violation of global scale symmetry associated with RGE functions. As a result of the quantum scale invariant regularization being implemented, the scale symmetry is preserved at the quantum level despite the RGE functions being non-zero, as can be inspected at the level of composite quantum operators that govern dilatation of Green functions. We analyze these statements in explicit detail using a specific but easily generalized toy model with scalar fields.

hep-th↗

arXiv2018

Hill-climbing dark inflation

Within the framework of the scalar-tensor theory we consider a hill-climbing inflation, in which the effective Planck mass increases in time. We obtain the Einstein frame potential with infinitely long and flat plateau as we approach towards the strong coupling regime, together with a run-away vacuum in the GR limit of the theory. The inflation ends with the scalar field rolling down towards infinity, which at the effective level indicates the massless scalar field domination in the Universe. In this scheme we assume that the inflaton is a dark particle, which has no couplings to the Standard Model degrees of freedom (other than the gravitational ones). We discuss the gravitational reheating of the Universe together with its implications on the predictions of the model, including possible amplification of primordial gravitational waves. Our model for the first time realizes explicitly the enhancement of the primordial gravitational waves in the dark inflation scenario.

astro-ph.CO↗

arXiv2017

Gravitational wave signals and cosmological consequences of gravitational reheating

Reheating after inflation can proceed even if the inflaton couples to Standard Model (SM) particles only gravitationally. However, particle production during the transition between de-Sitter expansion and a decelerating Universe is rather inefficient and the necessity to recover the visible Universe leads to a non-standard cosmological evolution initially dominated by remnants of the inflaton field. We remain agnostic to the specific dynamics of the inflaton field and discuss a generic scenario in which its remnants behave as a perfect fluid with a general barotropic parameter $w$. Using CMB and BBN constraints we derive the allowed range of inflationary scales. We also show that this scenario results in a characteristic primordial Gravitational Wave (GW) spectrum which gives hope for observation in upcoming runs of LIGO as well as in other planned experiments.

astro-ph.CO↗

arXiv2017

Domain walls in the extensions of the Standard Model

Our main interest is the evolution of domain walls of the Higgs field in the early Universe. The aim of this paper is to understand how dynamics of Higgs domain walls could be influenced by yet unknown interactions from beyond the Standard Model. We assume that the Standard Model is valid up to certain, high, energy scale $Λ$ and use the framework of the effective field theory to describe physics below that scale. Performing numerical simulations with different values of the scale $Λ$ we are able to extend our previous analysis and determine its range of validity. We study domain walls interpolating between the physical electroweak vacuum and the vacuum appearing at very high field strengths. These domain walls could be formed from non-homogeneous configurations of the Higgs field produced by quantum fluctuations during inflation or thermal fluctuations during reheating. Our numerical simulations show that evolution of Higgs domain walls is rather insensitive to interactions beyond the Standard Model as long as masses of new particles are grater than $10^{12}\ \textrm{GeV}$. For lower values of $Λ$ the RG improved effective potential is strongly modified at field strengths crucial to the evolution of domain walls. For instance its minima become degenerate for $Λ$ around $10^{11}\ \textrm{GeV}$. We find that even in the case when the minima of the potential are nearly degenerate Higgs domain walls decayed shortly after their formation for generic initial conditions. On the other hand, in simulations with specifically chosen initial conditions Higgs domain walls can live longer and enter the scaling regime. We also determine the energy spectrum of gravitational waves produced by decaying domain walls of the Higgs field. For generic initial field configurations the amplitude of the signal is too small to be observed in present and planned detectors.

hep-ph↗

arXiv2017

Dynamical relaxation in 2HDM models

The dynamical relaxation provides an interesting solution to the hierarchy problem in face of the missing signatures of any new physics in recent experiments. Through a dynamical process taking place in the inflationary phase of the universe it manages to achieve a small electroweak scale without introducing new states observable in current experiments. Appropriate approximation makes it possible to derive an explicit formula for the final vevs in the double-scanning scenario extended to the two Higgs doublet models (2HDM). Analysis of the relaxation in 2HDM indicates, that in a general case it is impossible to keep vevs of both scalars small, unless fine-tuning is present or additional symmetries are cast upon the Lagrangian. Within the slightly constrained variant of 2HDM, where odd powers of the fields' expectation values are not present (which can be easily enforced by requiring that the doublets have different gauge transformations or by imposing a global symmetry) it is shown that the the difference between the vevs of two scalars tends to be proportional to the cutoff. The analysis of the relaxation in 2HDM indicates, that in a~general case the relaxation would be stopped by the first doublet that gains a vev, with the other one remaining vevless with a mass of the order of the cutoff. This happens to conform with the inert doublet model.

hep-ph↗

arXiv2017

Quenching preheating by light fields

In this paper we investigate the role of additional light fields not directly coupled to the background during preheating. We extend our previous study that proved that the production of particles associated with such fields can be abundant due to quantum corrections, even for the massless states. We also obtain the expression for the occupation number operator in terms of interacting fields which includes the non-linear effects important for non-perturbative particle production. We show that adding too many light degrees of freedom without direct interactions with the background might attenuate or even quench preheating as the result of backreaction effects.

hep-ph↗