arXiv subjects

Fernando Mendez

Publications and source records attributed to Fernando Mendez.

9 recordsLinked to original sources

arXiv2025

Graviton Scattering on Gravitational Atoms: Relic Graviton Shot Noise

We study the scattering of a graviton on a gravitational atom. By gravitational atom we mean a quantum mechanical system of a gravitational (bound) state of two massive particles, with possibly some boundary conditions (such as bouncing on a table or hanging as a pendulum). We demonstrate the unexpected fact, that the total absorption cross section is universal, it is independent of both the mass of the gravitationally bound particle or of the mass providing the binding potential. We find that the total absorption cross-section is simply proportional to the Planck area, multiplied by a dimensionless, numerical factor. We speculate about the potential for detection of relic gravitons shot noise.

hep-th↗

arXiv2023

Dark Matter in a bi-metric universe

We study the possibility to describe dark matter in a model of the universe with two scale factors and a non-standard Poisson bracket structure characterized by the deformation parameter \kappa. The dark matter evolution is analyzed in the early stages of the universe, and its relic density is obtained via the Freeze-In and Freeze-Out mechanism. We show that by fixing \k{appa} and the initial ratio of energy densities present in the different sectors of the universe, the space of thermal average annihilation cross-sections and dark matter masses compatible with the standard cosmology prior to Big Bang Nucleosynthesis (BBN), is enlarged. This feature of the model is compatible with non-standard cosmology.

hep-ph↗

arXiv2021

Bi-metric Universe with Matter

We analyze the early stage of evolution of a universe with two scale factors proposed in [1] when matter is present. The scale factors describe two causally disconnected patches of the universe interacting trough a non-trivial Poisson bracket structure in the momentum sector characterized by one parameter κ. We studied two scenarios in which one of the patches is always filled with relativistic matter while the other contains relativistic matter in one case, and non-relativistic matter in the second case. By solving numerically the set of equations governing the dynamics, we found that the energy content of one sector drains to the other and from here it is possible to constraint the deformation parameter κby imposing that the decay of the energy density happens, at most, at the Big Bang Nucleosynthesis temperature in order to return to the usual behavior of radiation. The relation with Non Standard Cosmologies is also addressed.

gr-qc↗

arXiv2015

Extracting Hidden-Photon Dark Matter From an LC-Circuit

We point out that a cold dark matter condensate made of gauge bosons from an extra hidden U(1) sector - dubbed hidden- photons - can create a small, oscillating electric density current. Thus, they could also be searched for in the recently proposed LC-circuit setup conceived for axion cold dark matter search by Sikivie, Sullivan and Tanner. We estimate the sensitivity of this setup for hidden-photon cold dark matter and we find it could cover a sizable, so far unexplored parameter space.

hep-ph↗

arXiv2015

Cosmic Four-Fermion Neutrino Secret Interactions, Enhancement and Total Cross Section

The scattering of neutrinos assuming a "secret" interaction at low energy is considered. To leading order in energy, the two-body potential is a $δ$-potential, and it is used as a motivation to study generic short-range elastic interactions between neutrinos. The scattering cross section and Sommerfeld enhancement depend on two phenomenological parameters deriving from the exact form of the potential, akin to "renormalized" coupling constants. Repulsive potentials lead to a decrease in the total cross section, resulting in an enhancement of the neutrino density. For attractive potentials of the right form, substantial Sommerfeld enhancement can appear.

hep-ph↗

arXiv2008

Effects of heavy bosonic excitations on QED vacuum

We discuss the contribution of axion-like excitations (ALE) to the vacuum birrefringence in the limit $m_A \gtrsim ω$, where $m_A$ is the mass of the excitation and $ω$ the energy of test photons interacting with an external (intense) magnetic field. The relevance of this term with respect to the QED contribution depends on the ratio $g_A/m_A$ and, from present bounds on the mass and the coupling constant $g_A$, we find that in the present low energy regime, it ranges from $10^{-14}$ to $10^2$ suggesting an interesting alternative to explore.

hep-ph↗

arXiv2007

CPT/Lorentz Invariance Violation and Neutrino Oscillation

We analyze the consequences of violation of Lorentz and $CPT$ invariance in the massless neutrino sector by deforming the canonical anti-commutation relations for the fields. We show that, for particular choices of the deformation, oscillation between massless neutrino species takes place when only Lorentz invariance is violated. On the other hand, if both Lorentz and $CPT$ invariances are violated, we show that there is no oscillation between massless neutrino species. Comparing with the existing experimental data on neutrino oscillations, we obtain bounds on the parameter for Lorentz invariance violation.

hep-ph↗

arXiv2006

CPT/Lorentz Invariance Violation and Quantum Field Theory

Analogies between the noncommutative harmonic oscillator and noncommutative fields are analyzed. Following this analogy we construct examples of quantum fields theories with explicit CPT and Lorentz symmetry breaking. Some applications to baryogenesis and neutrino oscillation are also discussed

hep-th↗

arXiv1998

A note on covariant action integrals in three dimensions

We compute -in the saddle point approximation- the partition function for the 2+1 black hole using the Gibbons-Hawking approach. Some issues concerning the definition of thermodynamical ensembles are clarified. It is pointed out that the right action in covariant form is exactly equal to the Chern-Simons action with no added boundary terms. This action is finite, yields the right canonical free energy and has an extremum when the temperature and angular velocity are fixed. The correspondence with a 1+1 $CFT$ is indicated.

hep-th↗