arXiv subjects

Samuel W. P. Oliveira

Publications and source records attributed to Samuel W. P. Oliveira.

5 recordsLinked to original sources

arXiv2026

Conformal anomaly in a vector field model with auxiliary scalar field

The conformal anomaly has well-known ambiguities related to the possible schemes of regularization and renormalization. In case of dimensional regularization, one of the options is to formulate the theory as conformal in the dimension $D \neq 4$. For a gauge vector field this can be done in several ways and one of the options is to introduce an auxiliary scalar playing the role of a compensator. The advantage of this approach is that it preserves gauge symmetry and avoids problems with possible violation of unitarity. We explore the consequences of introducing such an auxiliary field for the anomaly and anomaly-induced action. It is shown that the new scalar degree of freedom gains an independent dynamics after taking the $4D$ limit. The remnant scalar, also, demonstrates some interesting properties.

hep-th↗

arXiv2026

Bounce solutions with quantum vacuum effects of massive fields and subsequent Starobinsky inflation

We extend the previous work about the cosmological solutions with a bounce without modifications of gravity or introducing an extra scalar field. The main finding was that the bounce is possible in the initially contracting Universe filled with matter. After a strong contraction, matter gains the equation of state close to the one of radiation, such that the effect on matter on the evolution of the FLRW metric disappears at the classical level. However, this effect comes back owing to the quantum trace anomaly in the matter/radiation sector. In the present contribution, we explore the weak impact of massive fields on the anomaly-driven bounce solution and discuss the role of the vacuum terms. The masses are assumed small and regarded as small perturbations, which enables using trace anomaly even in this case. On the other hand, by adding the $R^2$ term to the action, we arrive at the model with the trans-Planckian bounce and subsequent Starobinsky inflation. In such a framework, using the numerical analysis, we consider three scenarios providing bounce solutions.

gr-qc↗

arXiv2026

Cosmological Singularities and Quantum Particles

We study if there is an opportunity to describe quantum particles in the vicinity of three types of cosmological singularities, big bang-big crunch, big rip and big brake. Writing down the Dirac equation for spinors, and choosing a convenient parametrization for basis functions of the spinor field, we show that the corresponding second-order differential equation has two independent solutions which are non-singular in the case of all three types of singularities. That permits us to construct the Fock space for the spinor particles and to interprete this fact as their opportunity to cross these cosmological singularities. We show also that this is impossible to do for scalar particles and changing the parametrization does not help. Thus, fermions look more resilient to the passage of the cosmological singularities than bosons.

gr-qc↗

arXiv2025

Trace anomaly for a conformal 2D vector field model

The trace anomaly and anomaly-induced action are evaluated for the two-dimensional $2D$ vector theory with classical conformal symmetry. Implementing local conformal symmetry while preserving the gauge invariance requires either giving up locality of the classical action or, equivalently, introducing an auxiliary scalar field. The two-dimensional limit in such a theory is singular. However, in the dimensional regularization, the limit $D \to 2$ in the one-loop divergence is smooth. As a result, we arrive at the expression for anomaly, which has a rich general structure, typical for the dimensions $D \geq 4$. For comparison and completeness, we also evaluate anomalies for conformal scalar and fermions, also in the presence of auxiliary external scalars.

hep-th↗

arXiv2024

Pauli equation and charged spin-1/2 particle in a weak gravitational field

Using the nonrelativistic approximation in the curved-space Dirac equation, the analog of the Pauli equation is derived for a weak gravitational field with a gauge fixing condition related to the synchronous gauge, in the presence of an electromagnetic field. Different from the previous works which were employing either the exact or conventional Foldy-Wouthuysen transformations, here we perform calculations by directly performing nonrelativistic approximation which reduced in the power series expansion in the inverse mass of the spinning particle. On top of that, the equations of motion for the massive spin-$1/2$ charged particle are obtained. The two particular cases of the previously explored backgrounds, namely a) plane gravitational wave and b) homogeneous static gravitational field are considered for control. In the case a) we meet correspondence with the previous results. On the other hand, in case b), there is no correspondence with neither perturbative nor with exact Foldy-Wouthuysen transformations, which we also recalculate and agree with the previous works. The disagreement is a kind of a theoretical challenge and most likely occurs because the potential energy, in the particular case of Newtonian approximation, is proportional to the mass of the particle.

gr-qc↗