arXiv subjects

Gabriella Piccinelli

Publications and source records attributed to Gabriella Piccinelli.

At least 19 recordsLinked to original sources

arXiv2023

Particle interaction strengths modified by magnetic fields

Magnetic fields are everywhere in the Universe and in our everyday life and many processes are affected by their presence, generating a rich phenomenology that depends also on other possible external agents. We review here some results, both from our workgroup and from other research groups, about the effect of magnetic fields on particles interaction processes, focusing mainly on recent results, but without losing sight on early seminal works on this topic. A vast assortment of physical situations and of analytical and numerical approaches can be found in the literature in this subject, making the comparison between them not straightforward. Our aim is to focus attention on differences and similarities between the different situations and approaches, looking for a systematization scheme that could be predictive, once the role played by each physical ingredient could be understood. The main purpose of this work is to find some physical explanations of the ongoing processes.

hep-ph↗

arXiv2022

Toward a magnetic warm inflation scenario

In this work we explore the effects that a possible primordial magnetic field can have on the inflaton effective potential, taking as the underlying model a warm inflation scenario, based on global supersymmetry with a new-inflation-type potential. The decay scheme for the inflaton field is a two-step process of radiation production, where the inflaton couples to heavy intermediate superfields, which in turn interact with light particles. In this context, we consider that both sectors, heavy and light, are charged and work in the strong magnetic field approximation for the light fields. We find an analytical expression for the one-loop effective potential, for an arbitrary magnetic field strength, and show that the trend of the magnetic contribution is to make the potential flatter in the origin's vicinity, preserving the conditions for a successful inflationary process. This result is backed up by the behavior of slow-roll parameter $ε$. The viability of this magnetic warm inflation scenario is also supported by the estimation of the effect of the magnetic field on the heavy particles decay width.

hep-ph↗

arXiv2021

Implementation of two-field inflation for cosmic linear anisotropy solving system

We outline the modifications in the numerical Boltzmann code Cosmic Linear Anisotropy Solving System (CLASS) in order to include extra inflationary fields. The functioning of the code is first described, how and where modifications are meant to be done are later explained. In the present study, we focus on the modifications needed for the implementation of a two-field inflationary model, with canonical kinetic terms and a polynomial potential with no cross terms, presenting preliminary results for the effect of the second field on the spectra. The adaptability of the code is exploited, making use of the classes and structures of C and the generic Runge-Kutta integration tool provided by the program.

astro-ph.CO↗

arXiv2020

Inflationary predictions of Geometric Inflation

In the framework of gravitational models obtained from the Geometric Inflation's proposal, where an infinite tower of curvature scalars are included into the action, we compute the slow-roll parameters by the Hubble slow-roll approach. We test the viability of such models as inflationary scenarios, focusing on the tensor-to-scalar ratio, $r$, and spectral scalar index, $n_s$, relation. We find that all models considered here produce inflation and, most of them coincide, some better than others, with the marginalized 95$\%$ CL region given by Planck's data collaboration.

gr-qc↗

arXiv2018

Response to an External Magnetic Field of the Decay Rate of a Neutral Scalar Field into a Charged Fermion Pair

In this work we explore the effects of a weak magnetic field on the decay process of a neutral scalar boson into a pair of charged fermions in vacuum. Since the analytical computation of the decay width needs of some approximation, following two different approaches, we study the low and high transverse momentum limits. Our findings indicate that the magnetic field effect depends on the kinematics of the scalar particle.

hep-ph↗

arXiv2018

Kicks of magnetized strange quark stars induced by anisotropic emission of neutrinos

We study the anisotropic neutrino emission from the core of neutron stars induced by the star's magnetic field. We model the core as made out of a magnetized ideal gas of strange quark matter and implement the conditions for stellar equilibrium in this environment. The calculation is performed without resorting to analytical simplifications and for temperature, density and magnetic field values corresponding to typical conditions for a neutron star's evolution. The anisotropic neutrino emission produces a rocket effect that contributes to the star's kick velocity. We find that the computed values for the kick velocity lie within the range of the observed values, reaching velocities of the order of $\sim1000$ km s$^{-1}$ for magnetic fields between $10^{15}-10^{18}$ G and radii of 20 to 5 km, respectively.

astro-ph.HE↗

arXiv2017

Magnetic Field Effect on Charged Scalar Pair Creation at Finite Temperature

In this work we explore the effects of a weak magnetic field and a thermal bath on the decay process of a neutral scalar boson into two charged scalar bosons. Our findings indicate that magnetic field inhibits while temperature enhances the pair production. The employed formalism allows us to isolate the contribution of magnetic fields in vacuum, leading to a separate analysis of the effects of different ingredients. This is essential since the analytical computation of the decay width necessarily needs of some approximation and the results that can be found in the literature are not always coincident. We perform the calculation in vacuum by two different weak field approximations. The particle pair production in vacuum was found to coincide with finite temperature behavior, which is opposite to results obtained by other authors in scenarios that involve neutral particles decaying into a pair of charged fermions. Among other differences between these scenarios, we traced that the analytical structure of the self-energy imposed by the spin of particles involved in the process is determinant in the behavior of the decay rate with the magnetic field.

hep-ph↗

arXiv2014

Warm inflation in the presence of magnetic fields

We study the effects of primordial magnetic fields on the inflationary potential in the context of a warm inflation scenario. The model, based on global supersymmetry with a new-inflation-type potential and a coupling between the inflaton and a heavy intermediate superfield, is already known to preserve the flatness required for slow-roll conditions even after including thermal contributions. Here we show that the magnetic field makes the potential even flatter, retarding the transition and rendering it smoother.

hep-ph↗

arXiv2013

Warm inflation in presence of magnetic fields

We present preliminary results on the possible effects that primordial magnetic fields can have for a warm inflation scenario, based on global supersymmetry, with a new-inflation-type potential. This work is motivated by two considerations: first, magnetic fields seem to be present in the universe on all scales, which rises the possibility that they could also permeate the early universe; second, the recent emergence of inflationary models where the inflaton is not assumed to be isolated but instead it is taken as an interacting field, even during the inflationary expansion. The effects of magnetic fields are included resorting to Schwinger proper time method.

astro-ph.CO↗

arXiv2011

Ferromagnetic properties of charged vector bosons condensate in the early universe

Bose-Einstein condensation in the early universe is considered. The magnetic properties of a condensate of charged vector bosons are studied, showing that a ferromagnetic state is formed. As a consequence, the primeval plasma may be spontaneously magnetized inside macroscopically large domains and primordial magnetic fields can be generated.

astro-ph.CO↗

arXiv2010

Symmetry restoration at finite temperature with weak magnetic fields

We study symmetry restoration at finite temperature in the standard model during the electroweak phase transition in the presence of a weak magnetic field. We compute the finite temperature effective potential up to the contribution of ring diagrams, using the broken phase degrees of freedom, and keep track of the gauge parameter dependence of the results. We show that under these conditions, the phase transition becomes stronger first order.

hep-ph↗

arXiv2010

Ferromagnetic properties of charged vector boson condensate

Bose-Einstein condensation of W bosons in the early universe is studied. It is shown that, in the broken phase of the standard electroweak theory, condensed W bosons form a ferromagnetic state with aligned spins. In this case the primeval plasma may be spontaneously magnetized inside macroscopically large domains and form magnetic fields which may be seeds for the observed today galactic and intergalactic fields. However, in a modified theory, e.g. in a theory without quartic self interactions of gauge bosons or for a smaller value of the weak mixing angle, antiferromagnetic condensation is possible. In the latter case W bosons form scalar condensate with macroscopically large electric charge density i.e. with a large average value of the bilinear product of W-vector fields but with microscopically small average value of the field itself.

astro-ph.CO↗

arXiv2009

Screening effects in plasma with charged Bose condensate

Screening of Coulomb field of test charge in plasma with Bose condensate of electrically charged scalar field is considered. It is found that the screened potential contains several different terms: one decreases as a power of distance (in contrast to the usual exponential Debye screening), some other oscillate with an exponentially decreasing envelope. Similar phenomenon exists for fermions (Friedel oscillations), but fermionic and bosonic systems have quite different features. Several limiting cases and values of the parameters are considered and the resulting potentials are presented.

hep-ph↗

arXiv2009

Electrodynamics at non-zero temperature, chemical potential, and Bose condensate

Electrodynamics of charged scalar bosons and spin 1/2 fermions is studied at non-zero temperature, chemical potentials, and possible Bose condensate of the charged scalars. Debye screening length, plasma frequency, and the photon dispersion relation are calculated. It is found that in presence of the condensate the time-time component of the photon polarization operator in the first order in electric charge squared acquires infrared singular parts proportional to inverse powers of the spatial photon momentum k.

hep-th↗

arXiv2008

Feynman parametrization and Mellin summation at finite temperature

We show that the Mellin summation technique (MST) is a well defined and useful tool to compute loop integrals at finite temperature in the imaginary-time formulation of thermal field theory, especially when interested in the infrared limit of such integrals. The method makes use of the Feynman parametrization which has been claimed to have problems when the analytical continuation from discrete to arbitrary complex values of the Matsubara frequency is performed. We show that without the use of the MST, such problems are not intrinsic to the Feynman parametrization but instead, they arise as a result of (a) not implementing the periodicity brought about by the possible values taken by the discrete Matsubara frequencies before the analytical continuation is made and (b) to the changing of the original domain of the Feynman parameter integration, which seemingly simplifies the expression but in practice introduces a spurious endpoint singularity. Using the MST, there are no problems related to the implementation of the periodicity but instead, care has to be taken when the sum of denominators of the original amplitude vanishes. We apply the method to the computation of loop integrals appearing when the effects of external weak magnetic fields on the propagation of scalar particles is considered.

hep-ph↗

arXiv2008

Minimal Standard Model self-energies at finite temperature in the presence of weak magnetic fields: towards a full symmetry restoration study

The study of the universe's primordial plasma at high temperature plays an important role when tackling different questions in cosmology, such as the origin of the matter-antimatter asymmetry. In the Minimal Standard Model (MSM) neither the amount of CP violation nor the strength of the phase transition are enough to produce and preserve baryon number during the Electroweak Phase Transition (EWPT), which are two of the three ingredients needed to develop baryon asymmetry. In this talk we present the first part of the analysis done within a scenario where it is viable to have improvements to the aforementioned situation: we work with the degrees of freedom in the broken symmetry phase of the MSM and analyze the development of the EWPT in the presence of a weak magnetic field. More specifically, we calculate the particle self-energies that include the effects of the weak magnetic field, needed for the MSM effective potential up to ring diagrams.

hep-ph↗

arXiv2006

Effective potential at finite temperature in a constant hypermagnetic field: Ring diagrams in the Standard Model

We study the symmetry breaking phenomenon in the standard model during the electroweak phase transition in the presence of a constant hypermagnetic field. We compute the finite temperature effective potential up to the contribution of ring diagrams in the weak field, high temperature limit and show that under these conditions, the phase transition becomes stronger first order.

hep-th↗

arXiv2005

Effective potential at finite temperature in a constant magnetic field I: Ring diagrams in a scalar theory

We study symmetry restoration at finite temperature in the theory of a charged scalar field interacting with a constant, external magnetic field. We compute the finite temperature effective potential including the contribution from ring diagrams. We show that in the weak field case, the presence of the field produces a stronger first order phase transition and that the temperature for the onset of the transition is lower, as compared to the case without magnetic field.

hep-ph↗