arXiv subjects

Zygmunt Lalak

Publications and source records attributed to Zygmunt Lalak.

At least 37 records · Page 2Linked to original sources

arXiv2017

Non-minimally coupled gravity and vacuum stability

We investigate the properties of vacuum decay taking into account a non-minimal coupling to gravity. We extend the standard thin-wall solution to include the non-minimal coupling and verify its validity by comparison with a full numerical study. We also investigate the implications of a~large cosmological constant whose influence on the geometry boosts the tunneling rate. Our analysis shows that the influence of the non-minimal coupling differs significantly between the cases of Minkowski and deSitter backgrounds.

hep-ph↗

arXiv2017

Darkflation -- one scalar to rule them all?

The problem of explaining both inflationary and dark matter physics in the framework of a minimal extension of the Standard Model was investigated. To this end, the Standard Model completed by a real scalar singlet playing a role of the dark matter candidate has been considered. We assumed both the dark matter field and the Higgs doublet to be nonminimally coupled to gravity. Using quantum field theory in curved spacetime we derived an effective action for the inflationary period and analyzed its consequences. In this approach, after integrating out both dark matter and Standard Model sectors we obtained the effective action expressed purely in terms of the gravitational field. We paid special attention to determination, by explicit calculations, of the form of coefficients controlling the higher-order in curvature gravitational terms. Their connection to the Standard Model coupling constants has been discussed.

gr-qc↗

arXiv2016

Domain walls and gravitational waves in the Standard Model

We study domain walls which can be created in the Standard Model under the assumption that it is valid up to very high energy scales. We focus on domain walls interpolating between the physical electroweak vacuum and the global minimum appearing at very high field strengths. The creation of the network which ends up in the electroweak vacuum percolating through the Universe is not as difficult to obtain as one may expect, although it requires certain tuning of initial conditions. Our numerical simulations confirm that such domain walls would swiftly decay and thus cannot dominate the Universe. We discuss the possibility of detection of gravitational waves produced in this scenario. We have found that for the standard cosmology the energy density of these gravitational waves is too small to be observed in present and planned detectors.

astro-ph.CO↗

arXiv2016

Implications of extreme flatness in a general f(R) theory

We discuss a modified gravity theory defined by $f(R) = \sum_{n}^{l} α_n M^{2(1-n)} R^n$. We consider both finite and infinite number of terms in the series while requiring that the Einstein frame potential of the theory has a flat area around any of its stationary points. We show that the requirement of maximally flat stationary point leads to the existence of the saddle point (local maximum) for even (odd) $l$. In both cases for $l\to\infty$ one obtains the Starobinsky model with small, exponentially suppressed corrections. Besides the GR minimum the Einstein frame potential has an anti de Sitter vacuum. However we argue that the GR vacuum is absolutely stable and AdS cannot be reached neither via classical evolution nor via quantum tunnelling. Our results show that a Starobinsky-like model is the only possible realisation of $f(R)$ theory with an extremely flat area in the Einstein frame potential.

hep-th↗

arXiv2016

Multi-phase induced inflation in theories with non-minimal coupling to gravity

In this paper we investigate the induced inflation with two flat regions: one Starobinsky-like plateau in big field regime and one shorter plateau around the saddle point of the Einstein frame potential. This multi-phase inflationary scenario can be used to solve the problem of classical cosmology. The inflation at the saddle-point plateau is consistent with the data and can have arbitrarily low scale. The results can be useful in the context of the Higgs-Axion relaxation and in a certain limit they are equivalent to the $α$-attractors.

astro-ph.CO↗

arXiv2016

The impact of non-minimally coupled gravity on vacuum stability

We consider vacuum decay in the presence of a non-minimal coupling to gravity. We extend the usual thin-wall solution to include the non-minimal coupling. We also perform a full numerical study and discuss the validity of the new thin-wall approximation. Implications of a large cosmological constant, whose influence on the geometry boosts the tunnelling rate, are discussed. Our results show that the influence of the non-minimal coupling differs significantly between the cases of Minkowski and deSitter backgrounds. In the latter the decay probability quickly decreases when the coupling grows and in fact the vacuum can be made absolutely stable simply due to introduction of the non-minimal coupling. In the case of Minkowski background the effect is much weaker and the decay rate even increases for small values of the non-minimal coupling.

hep-ph↗

arXiv2016

Gauge fixing and renormalisation scale independence of tunneling rate in abelian Higgs model and in the Standard Model

We explicitly show perturbative gauge fixing independence of the tunneling rate to a stable radiatively induced vacuum in the abelian Higgs model. We work with a class of $R_ξ$ gauges in the presence of both dimensionless and dimensionful gauge fixing parameters. We show that Nielsen identities survive the inclusion of higher order oparators and compute the tunnelling rate to the vacua modified by the nonrenormalisable operators in a gauge invariant manner. We also discuss implications of this method for the complete Standard Model.

hep-ph↗

arXiv2015

Gravity and the stability of the Higgs sector

We pursued the question of the influence of a strong gravitational field on the structure of the Higgs effective potential in the gauge-less top-Higgs sector of the Standard Model with an additional scalar singlet. To this end, we calculated the one-loop corrected effective potential in an arbitrary curved spacetime. We have found that the gravity induced terms in the effective potential may influence its behavior in both small and large field regions. This result indicated the necessity of a more careful investigation of the effect of high curvature in the problems concerning the stability of the Higgs effective potential in the full Standard Model.

hep-th↗

arXiv2015

Suppressing gravitino thermal production with a temperature-dependent messenger coupling

We show that the constraints on GMSB theories from the gravitino cosmology can be significantly relaxed if the messenger-spurion coupling is temperature dependent. We demonstrate this novel mechanism in a scenario in which this coupling depends on the VEV of an extra singlet field $S$ that interacts with the thermalized plasma which can result in a significantly suppressed gravitino production rate. In such a scenario the relic gravitino abundance is determined by the thermal dynamics of the $S$ field and it is easy to fit the observed dark matter abundance evading the stringent constraints on the reheating temperature, thus making gravitino dark matter consistent with thermal leptogenesis.

hep-ph↗

arXiv2015

Saddle point inflation from higher order corrections to Higgs/Starobinsky inflation

We explore two saddle point inflationary scenarios in the context of higher order corrections related to different generalisations of general relativity. Firstly, we deal with Jordan frame Starobinsky potential, for which we identify a portion of a parameter space of inflection point inflation, which can accommodate all the experimental results. Secondly, we analyse Higgs inflation and more specifically the influence of non-renormalisible terms on the standard quartic potential. All results were verified with the PLANCK 2015 data.

hep-th↗

arXiv2015

Features of electroweak symmetry breaking in five dimensional SUSY models

We explore the phenomenological predictions of a supersymmetric standard model, with a large extra dimension and unifying gauge couplings. The modified five dimensional renormalisation group equations make it possible to obtain light, maximally mixed stops, with a low scale of supersymmetry breaking and a low unification scale. This allows the fine-tuning to be lowered right down to the barrier coming directly from experimental lower limits on the stop masses. We also show that attempts at modifying the SUSY breaking pattern to obtain more natural soft terms at the high scale do not give the expected fine-tuning relaxation, and only RGE effects turn out to be effective in generating a lower fine-tuning.

hep-ph↗

arXiv2015

Stability of the effective potential of the gauge-less top-Higgs model in curved spacetime

We investigate stability of the Higgs effective potential in curved spacetime. To this end, we consider the gauge-less top-Higgs sector with an additional scalar field. Explicit form of the terms proportional to the squares of the Ricci scalar, the Ricci tensor and the Riemann tensor that arise at the one-loop level in the effective action has been determined. We have investigated the influence of these terms on the stability of the scalar effective potential. The result depends on background geometry. In general, the potential becomes modified both in the region of the electroweak minimum and in the region of large field strength.

hep-th↗

arXiv2015

Inflation and dark energy from $f(R)$ gravity

Inflationary paradigm has several issues, such as the pre-inflationary horizon problem or the eternal inflation. To avoid that the standard Starobinsky inflation has been extended to $R + αR^n$ and $R + αR^n -δR^{2-n}$ models as well as Brans-Dicke generalisation of those $f(R)$ models. The region of the parameter space, which provides consistency with PLANCK data and lack of eternal inflation has been founded. The Einstein frame potential has a stable minimum with non-zero vacuum energy, which may be a source of dark energy.

hep-th↗

arXiv2015

Standard Model vacuum stability in the presence of gauge invariant nonrenormalizable operators

Analysis of the Standard Model effective potential can reveal certain properties of the UV completion of SM. We discuss the issue of stability of the SM potential after inclusion of new nonrenormalizable interactions. We present the map of lifetimes resulting from different configurations of the new operators. The key result is proof of gauge independence of our results after inclusion of nonrenormalizable operators. We also discuss the consequences of RGE improvement of the potential.

hep-ph↗

arXiv2015

Naturalness of effective theories in Wilsonian approach

We have computed Wilsonian effective action in a simple model containing scalar field with quartic self-coupling which interacts via Yukawa coupling with a Dirac fermion. The model is invariant under a chiral parity operation, which can be spontaneously broken by a vev of the scalar field. We have computed explicitly Wilsonian running of relevant parameters which makes it possible to discuss in a consistent manner the issue of fine-tuning and stability of the scalar potential. This has been compared with the typical picture based on Gell-Mann-Low running. Since Wilsonian running includes automatically integration out of heavy degrees of freedom, the running differs markedly from the Gell-Mann-Low version. However, similar behavior can be observed: scalar mass squared parameter and the quartic coupling can change sign from a positive to a negative one due to running which causes spontaneous symmetry breaking or an instability in the renormalizable part of the potential for a given range of scales. As for the issue of fine-tuning, since in the Wilsonian approach power-law terms are not subtracted, one can clearly observe the quadratic sensitivity of fine-tuning measure to the change of the cut-off scale.

hep-ph↗

arXiv2015

Particle production in the background with VEV depending on time

It is known that time-dependent vacuum expectation value of the background field may lead to abundant particle production in the early Universe. In supersymmetric theories bosons and fermions are produced in a correlated manner that depends on the details of the supersymmetric scenario. Paper presents the general method of calculating the number density of produced particles based on the WKB approximation and the generalized Bogoliubov transformation law. The impact of the backreaction and rescattering is emphasized, also in models with more than one coupling constant.

hep-ph↗

arXiv2015

Influence of interactions on particle production induced by time-varying mass terms

We have investigated effects of interaction terms on non-perturbative particle production. It is well known that time-varying masses induce abundant particle production. In this paper we have shown that it is possible to induce particle production even if the mass term of a particle species is not varying in time. Such particles are produced through the interactions with other fields, whose mass terms are varying due to a time-dependent background. The necessary formalism has been introduced and analytic and numerical calculations have been performed in a simple but illustrative model. The rather general result is that the amount of produced particles without time-dependent masses can be comparable with the particle density produced directly by the varying background if the strength of interaction terms is reasonably large.

hep-ph↗

arXiv2015

Saddle point inflation from $f(R)$ theory

We analyse several saddle point inflationary scenarios based on power-law $f(R)$ models. We investigate inflation resulting from $f(R) = R + α_n M^{2(1-n)}R^n + α_{n+1}M^{-2n}R^{n+1}$ and $f(R) = \sum_n^l α_n M^{2(1-n)} R^n$ as well as $l\to\infty$ limit of the latter. In all cases we have found relation between $α_n$ coefficients and checked consistency with the PLANCK data as well as constraints coming from the stability of the models in question. Each of the models provides solutions which are both stable and consistent with PLANCK data, however only in parts of the parameter space where inflation starts on the plateau of the potential, some distance from the saddle. And thus all the correct solutions bear some resemblance to the Starobinsky model.

gr-qc↗