
Araujo Filho, A. A. (2023). Thermodynamics of massless particles in curved spacetime. Int. J. Geom. Methods Mod. Phys., 12(13), 2350226–40pp.
Abstract: This work is devoted to study the behavior of massless particles within the context of curved spacetime. In essence, we investigate the consequences of the scale factor C(?) of the FriedmannRobertsonWalker metric in the Einsteinaether formalism to study photonlike particles. To do so, we consider the system within the canonical ensemble formalism in order to derive the following thermodynamic state quantities: spectral radiance, Helmholtz free energy, pressure, entropy, mean energy and the heat capacity. Moreover, the correction to the StefanBoltzmann law and the equation of states are also provided. Particularly, we separate our study within three distinct cases, i.e. s = 0, p = 0; s = 1, p = 1; s = 2, p = 1. In the first one, the results are derived numerically. Nevertheless, for the rest of the cases, all the calculations are accomplished analytically showing explicitly the dependence of the scale factor C(?) and the Riemann zeta function ?(s). Furthermore, our analyses are accomplished in general taking into account three different regimes of temperature of the universe, i.e. the inflationary era (T = 10(13)GeV), the electroweak epoch (T = 10(3)GeV) and the cosmic microwave background (T = 10(13)GeV).



Araujo Filho, A. A., Reis, J. A. A. S., & Ghosh, S. (2023). Quantum gases on a torus. Int. J. Geom. Methods Mod. Phys., 20(10), 2350178–19pp.
Abstract: This paper is aimed at studying the thermodynamic properties of quantum gases confined to a torus. To do that, we consider noninteracting gases within the grand canonical ensemble formalism. In this context, fermions and bosons are taken into account and the calculations are properly provided in both analytical and numerical manners. In particular, the system turns out to be sensitive to the topological parameter under consideration: the winding number. Furthermore, we also derive a model in order to take into account interacting quantum gases. To corroborate our results, we implement such a method for two different scenarios: a ring and a torus.



Capozziello, S., Harko, T., Lobo, F. S. N., Olmo, G. J., & Vignolo, S. (2014). The Cauchy problem in hybrid metricPalatini f(X)gravity. Int. J. Geom. Methods Mod. Phys., 11(5), 1450042–12pp.
Abstract: The wellformulation and the wellposedness of the Cauchy problem are discussed for hybrid metricPalatini gravity, a recently proposed modified gravitational theory consisting of adding to the EinsteinHilbert Lagrangian an f(R)term constructed a la Palatini. The theory can be recast as a scalartensor one predicting the existence of a light longrange scalar field that evades the local Solar System tests and is able to modify galactic and cosmological dynamics, leading to the latetime cosmic acceleration. In this work, adopting generalized harmonic coordinates, we show that the initial value problem can always be wellformulated and, furthermore, can be wellposed depending on the adopted matter sources.



Izadi, A., Shacker, S. S., Olmo, G. J., & Banerjee, R. (2018). Observational effects of varying speed of light in quadratic gravity cosmological models. Int. J. Geom. Methods Mod. Phys., 15(5), 1850084–16pp.
Abstract: We study different manifestations of the speed of light in theories of gravity where metric and connection are regarded as independent fields. We find that for a generic gravity theory in a frame with locally vanishing affine connection, the usual degeneracy between different manifestations of the speed of light is broken. In particular, the spacetime causal structure constant (c(ST)) may become variable in that local frame. For theories of the form f(R, Rmu nu Rmu nu), this variation in c(ST) has an impact on the definition of the luminosity distance (and distance modulus), which can be used to confront the predictions of particular models against Supernovae type Ia (SN Ia) data. We carry out this test for a quadratic gravity model without cosmological constant assuming (i) a constant speed of light and (ii) a varying speed of light (VSL), and find that the latter scenario is favored by the data.



Sepehri, A., Pincak, R., & Olmo, G. J. (2017). Mtheory, graphenebranes and superconducting wormholes. Int. J. Geom. Methods Mod. Phys., 14(11), 1750167–32pp.
Abstract: Exploiting an Mbrane system whose structure and symmetries are inspired by those of graphene (what we call a graphenebrane), we propose here a similitude between two layers of graphene joined by a nanotube and wormholes scenarios in the brane world. By using the symmetries and mathematical properties of the Mbrane system, we show here how to possibly increase its conductivity, to the point of making it as a superconductor. The questions of whether and under which condition this might point to the corresponding real graphene structures becoming superconducting are briefly outlined.

