arXiv subjects

Luis G. Cabral-Rosetti

Publications and source records attributed to Luis G. Cabral-Rosetti.

14 recordsLinked to original sources

arXiv2016

Anapole moment of the lightest neutralino in the cMSSM

We study the anapole moment of the lightest neutralino in the constrained Minimal Supersymmetric Standard Model (cMSSM). The electromagnetic anapole is the only allowed electromagnetic form factor for Majorana fermions, such as the neutralino. Since the neutralino is the LSP in many versions of the MSSM and therefore a candidate for dark matter, its characterization through its electromagnetic properties is important both for particle physics and for cosmology. We perform a scan in the parameter space of the cMSSM and find that the anapole moment is different from zero albeit very small ($< 10^{-3}$ GeV$^{-2}$). Combined with experimental constraints like the Higgs mass and the DM relic density, the allowed region of parameter space lies within the reach of future direct DM searches. Thus, the anapole moment could be used as a complementary constraint when studying the parameter space of the cMSSM and other similar models.

hep-ph↗

arXiv2012

Toroidal dipole moment of the lightest neutralino in the cMSSM

We study the toroidal dipole moment of the lightest neutralino in the constrained Minimal Supersymmetric Standard Model. The toroidal dipole moment is the only electromagnetic property of the neutralino. Since the neutralino is the LSP in many versions of the MSSM and therefore a candidate for dark matter, its characterization through its electromagnetic properties is important both for particle physics and for cosmology. We perform a scan in the parameter space of the cMSSM and find that the toroidal dipole moment is different from zero, albeit very small, in all the parameter space, and reaches a value around $10^{-3} \mathrm{GeV}^{-2}$ in a particular region of the parameter space, well below experimental bounds.

hep-ph↗

arXiv2008

Constraining the mSUGRA parameter space using the entropy of dark matter halos

We derive an expression for the entropy of a dark matter halo described by a Navarro-Frenk-White model with a core. The comparison of this entropy with the one of dark matter at the freeze-out era allows us to constraint the parameter space in mSUGRA models. Moreover, joining these constraints with the ones obtained from the usual abundance criteria and demanding both criteria to be consistent with the 2$σ$ bounds for the abundance of dark matter: $0.112\leqΩ_{DM}h^2\leq0.122$, we are able to clearly discriminate validity regions among the values of $\tan β$, one of the parameters of the mSUGRA model. We found that for the explored regions of the parameter space, small values of tan$β$ are not favored; only for tan$β\simeq50$ are both criteria significantly consistent. In the region where both criteria are consistent we also found a lower bound for the neutralino mass, $m_χ\geq 141$ GeV.

astro-ph↗

arXiv2006

Stellar polytropes and Navarro-Frenk-White halo models: comparison with observations

Motivated by the possible conflict between the Navarro-Frenk-White(NFW) model predictions for the dark matter contents of galactic systems and its correlation with baryonic surface density, we will explore an alternative paradigm for the description of dark matter halos. Such an alternative emerges from Tsallis' non-extensive thermodynamics applied to self-gravitating systems and leads to the so-called ``stellar polytrope'' (SP) model. We consider that this could be a better approach to real structures rather than the isothermal model, given the fact that the first one takes into account the non-extensivity of energy and entropy present in these type of systems characterized by long-range interactions. We compare a halo based on the Navarro-Frenk-White (NFW) and one which follows the SP description. Analyzing the dark matter contents estimated by means of global physical parameters of galactic disks, obtained from a sample of actual galaxies, with the ones of the unobserved dark matter halos, we conclude that the SP model is favored over the NFW model in such a comparison.

astro-ph↗

arXiv2006

Empirical testing of Tsallis' Thermodynamics as a model for dark matter halos

We study a dark matter halo model from two points of view: the ``stellar polytrope'' (SP) model coming from Tsallis' thermodynamics, and the one coming from the Navarro-Frenk-White (NFW) paradigm. We make an appropriate comparison between both halo models and analyzing the relations between the global physical parameters of observed galactic disks, coming from a sample of actual galaxies, with the ones of the unobserved dark matter halos, we conclude that the SP model is favored over the NFW model in such a comparison.

astro-ph↗

arXiv2006

Entropy considerations in constraining the mSUGRA parameter space

We explore the use of two criteria to constraint the allowed parameter space in mSUGRA models. Both criteria are based in the calculation of the present density of neutralinos as dark matter in the Universe. The first one is the usual ``abundance'' criterion which is used to calculate the relic density after the ``freeze-out'' era. To compute the relic density we used the numerical public code micrOMEGAs. The second criterion applies the microcanonical definition of entropy to a weakly interacting and self-gravitating gas evaluating then the change in the entropy per particle of this gas between the ``freeze-out'' era and present day virialized structures. An ``entropy-consistency'' criterion emerges by comparing theoretical and empirical estimates of this entropy. The main objective of our work is to determine for which regions of the parameter space in the mSUGRA model are both criteria consistent with the 2$σ$ bounds according to WMAP for the relic density: $0.0945<Ω_{CDM}h^2<0.1287$. As a first result, we found that for $A_0=0$, sgn$μ=+$, small values of tan$β$ are not favored; only for tan$β\simeq50$ are both criteria significantly consistent.

astro-ph↗

arXiv2005

Stellar polytropes and Navarro--Frenk--White dark matter halos: a connection to Tsallis entropy

We present an alternative for the description of galactic halos based on Tsallis' non--extensive entropy formalism; on this scheme, halos are stellar polytropes characterized by three parameters, the central density, $ρ_c$, the central velocity dispersion, $σ_c$ and the polytropic index, $n$. To evaluate these parameters we take the Navarro-Frenk-White paradigm as a comparative model and make the following assumptions: both halo models must have the same virial mass, the same total energy and the same maximal velocity. These three conditions fix all the parameters for a given stellar polytrope allowing us to compare both halo models. The halos studied have virial masses on the range $10^{12}-10^{15} M_\odot$, and it was found after the analysis that they are described, at all scales, by almost the same polytropic index, $n\approx 4.8$, implying an empirical estimation of Tsallis non--extensive parameter for this type of dynamical systems: $q\approx 1.3$.

astro-ph↗

arXiv2004

Using Entropy to Discriminate Annihilation Channels in Neutralinos Making up Galactic Halos

Applying the microcanonical definition of entropy to a weakly interacting and self--gravitating neutralino gas, we evaluate the change in the local entropy per particle of this gas between the freeze out era and present day virialized halo structures. An ``entropy consistency'' criterion emerges by comparing theoretical and empirical estimates of this entropy. We apply this criterion to the cases when neutralinos are mostly B-inos and mostly Higgsinos, in conjunction with the usual ``abundance'' criterion requiring that present neutralino relic density complies with $0.2<Ω_{\tildeχ^1_0} < 0.4$ for $h\simeq 0.65$. The joint application of both criteria reveals that a much better fitting occurs for the B-ino than for the Higgsino channels, so that the former seems to be a favored channel along the mass range of $155 \hbox{GeV} < m_{\tildeχ^1_0} < 230 \hbox{GeV}$. These results are consistent with neutralino annihilation patterns that emerge from recent theoretical analysis on cosmic ray positron excess data reported by the HEAT collaboration. The suggested methodology can be applied to test other annihilation channels of the neutralino, as well as other particle candidates of thermal WIMP gas relics.

hep-ph↗

arXiv2003

A New Method to Infere Which Type of Neutralinos Make Up Galactic Halos

Applying the microcanonical definition of entropy to a weakly interacting and self--gravitating neutralino gas, we evaluate the change in the local entropy per particle of this gas between the freeze out era and present day virialized halo structures. An ``entropy consistency'' criterion emerges by comparing the obtained theoretical entropy per particle of the virialized halos with an empirical entropy per particle given in terms of dynamical halo variables of actual galactic structures. We apply this criterion to the cases when neutralinos are mostly B-inos and mostly Higgsinos, in conjunction with the usual ``abundance'' criterion requiring that present neutralino relic density complies with $0.2<Ω_{\tildeχ^1_0} < 0.4$ for $h\simeq 0.65$. The joint application of both criteria reveals that a much better fitting occurs for the B-ino than for the Higgsino channels, so that the former seems to be a favored channel along the mass range of $150 \hbox{GeV} < m_{\tildeχ^1_0} < 250 \hbox{GeV}$. These results are consistent with neutralino annihilation patterns that emerge from recent theoretical analysis on cosmic ray positron excess data reported by the HEAT collaboration. The suggested methodology can be applied to test other annihilation channels of the neutralino, as well as other particle candidates of thermal WIMP gas relics.

hep-ph↗

arXiv2003

On the thermal footsteps of Neutralino relic gases

Current literature suggests that neutralinos are the dominant cold dark matter particle species. Assuming the microcanonical definition of entropy, we examine the local entropy per particle produced between the ``freeze out'' era to the present. An ``entropy consistency'' criterion emerges by comparing this entropy with the entropy per particle of actual galactic structures given in terms of dynamical halo variables. We apply this criterion to the cases when neutralinos are mosly b-inos and mostly higgsinos, in conjunction with the usual ``abundance'' criterion requiring that present neutralino relic density complies with $0.1 < Ω_{\chic{\tildeχ^0_1}} < 0.3$ for $h\simeq 0.65$. The joint application of both criteria reveals that a better fitting occurs for the b-ino channels, hence the latter seem to be favoured over the higgsino channels. The suggested methodology can be applied to test other annihilation channels of the neutralino, as well as other particle candidates of thermal gases relics.

hep-ph↗

arXiv2002

Appell Functions and the Scalar One-Loop Three-point Integrals in Feynman Diagrams

The scalar three-point function appearing in one-loop Feynman diagrams is compactly expressed in terms of a generalized hypergeometric function of two variables. Use is made of the connection between such Appell function and dilogarithms coming from a previous investigation. Special cases are obtained for particular values of internal masses and external momenta.

hep-ph↗

arXiv2002

Hydrodynamical description of Galactic Dark Matter

We consider simple hydrodynamical models of galactic dark matter in which the galactic halo is a self-gravitating and self-interacting gas that dominates the dynamics of the galaxy. Modeling this halo as a sphericaly symmetric and static perfect fluid satisfying the field equations of General Relativity, visible barionic matter can be treated as ``test particles'' in the geometry of this field. We show that the assumption of an empirical ``universal rotation curve'' that fits a wide variety of galaxies is compatible, under suitable approximations, with state variables characteristic of a non-relativistic Maxwell-Boltzmann gas that becomes an isothermal sphere in the Newtonian limit. Consistency criteria lead to a minimal bound for particle masses in the range $30 \hbox{eV} \alt m \alt 60 \hbox{eV}$ and to a constraint between the central temperature and the particles mass. The allowed mass range includes popular supersymmetric particle candidates, such as the neutralino, axino and gravitino, as well as lighter particles ($m\sim$ keV) proposed by numerical N-body simulations associated with self-interactive ``cold'' and ``warm'' dark matter structure formation theories.

hep-ph↗

arXiv2002

Hydrodynamics of galactic dark matter

We consider simple hydrodynamical models of galactic dark matter in which the galactic halo is a self-gravitating and self-interacting gas that dominates the dynamics of the galaxy. Modeling this halo as a sphericaly symmetric and static perfect fluid satisfying the field equations of General Relativity, visible barionic matter can be treated as ``test particles'' in the geometry of this field. We show that the assumption of an empirical ``universal rotation curve'' that fits a wide variety of galaxies is compatible, under suitable approximations, with state variables characteristic of a non-relativistic Maxwell-Boltzmann gas that becomes an isothermal sphere in the Newtonian limit. Consistency criteria lead to a minimal bound for particle masses in the range $30 \hbox{eV} \leq m \leq 60 \hbox{eV}$ and to a constraint between the central temperature and the particles mass. The allowed mass range includes popular supersymmetric particle candidates, such as the neutralino, axino and gravitino, as well as lighter particles ($m\approx$ keV) proposed by numerical N-body simulations associated with self-interactive CDM and WDM structure formation theories.

gr-qc↗

arXiv1998

Generalized Hypergeometric Functions and the Evaluation of Scalar One-loop Integrals in Feynman Diagrams

Present and future high-precision tests of the Standard Model and beyond for the fundamental constituents and interactions in Nature are demanding complex perturbative calculations involving multi-leg and multi-loop Feynman diagrams. Currently, large effort is devoted to the search for closed expressions of loop integrals, written whenever possible in terms of known - often hypergeometric-type - functions. In this work, the scalar three-point function is re-evaluated by means of generalized hypergeometric functions of two variables. Finally, use is made of the connection between such Appell functions and dilogarithms coming from a previous investigation, to recover well-known results.

hep-ph↗