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A. J. da Silva

Publications and source records attributed to A. J. da Silva.

At least 19 recordsLinked to original sources
arXiv2025

On the physical running of the electric charge in a dimensionless theory of gravity

We revisit the renormalization of the gauge coupling in massless QED coupled to a scaleless quadratic theory of gravity. We compare two alternative prescriptions for the running of the electric charge: (i) the conventional $μ$-running in minimal subtraction, and (ii) a ''physical'' running extracted from the logarithmic dependence of amplitudes on a hard scale $Q^{2}$ (e.g., $p^{2}$ or a Mandelstam invariant) after removing IR effects. At one loop, using dimensional regularization with an IR mass regulator $m$, we compute the photon vacuum polarization. We find a clean separation between UV and soft logarithms: the former is gauge and process independent and fixes the beta function, whereas the latter encodes nonlocal, IR-dominated contributions that may depend on gauge parameters and must not be interpreted as UV running. In the quadratic-gravity sector, the photon self-energy is UV finite--the $\lnμ^{2}$ pieces cancel--leaving only $\ln(Q^{2}/m^{2})$ soft logs. Consequently, quadratic gravity does not modify the one-loop UV coefficient and thus does not alter $β(e)$. Therefore, the physical running coincides with the $μ$-running in QED at one loop. Our analysis clarifies how to extract a gauge and process independent running in the presence of gravitational interactions and why soft logs from quadratic gravity should not contribute to $β(e)$.

hep-th↗
arXiv2024

Gravitational corrections to the two-loop beta function in a non-Abelian gauge theory

This paper investigates the coupling of massive fermions to gravity within the context of a non-Abelian gauge theory, utilizing the effective field theory framework for quantum gravity. Specifically, we calculate the two-loop beta function of the gauge coupling constant in a non-Abelian gauge theory, employing the one-graviton exchange approximation. Our findings reveal that gravitational corrections may lead to a non-trivial UV fixed point in the beta function of the gauge coupling constant, contingent upon the specific gauge group and the quantity of fermions involved.

hep-th↗
arXiv2023

On the supersymmetric pseudo-QED

Within the superfield approach, we discuss the three-dimensional supersymmetric (SUSY) pseudo-QED. We prove that it is all-loop renormalizable. We demonstrate that the SUSY pseudo-QED action can be generated as a quantum correction from the coupling of a spinor gauge superfield to a set of $N$ massless complex scalar superfields. Afterwards, we calculate the two-point function of the scalar superfields in the pseudo-QED which displays a divergence vanishing in a certain gauge.

hep-th↗
arXiv2022

Topological Superconductor from the Quantum Hall Phase: Effective Field Theory Description

We derive low-energy effective field theories for the quantum anomalous Hall and topological superconducting phases. The quantum Hall phase is realized in terms of free fermions with nonrelativistic dispersion relation, possessing a global $U(1)$ symmetry. We couple this symmetry with a background gauge field and compute the effective action by integrating out the gapped fermions. In spite of the fact that the corresponding Dirac operator governing the dynamics of the original fermions is nonrelativistic, the leading contribution in the effective action is a usual Abelian $U(1)$ Chern-Simons term. The proximity to a conventional superconductor induces a pairing potential in the quantum Hall state, favoring the formation of Cooper pairs. When the pairing is strong enough, it drives the system to a topological superconducting phase, hosting Majorana fermions. Even though the continuum $U(1)$ symmetry is broken down to a $\mathbb{Z}_2$ one, we can forge fictitious $U(1)$ symmetries that enable us to derive the effective action for the topological superconducting phase, also given by a Chern-Simons theory. To eliminate spurious states coming from the artificial symmetry enlargement, we demand that the fields in the effective action are $O(2)$ instead of $U(1)$ gauge fields. In the $O(2)$ case we have to sum over the $\mathbb{Z}_2$ bundles in the partition function, which projects out the states that are not $\mathbb{Z}_2$ invariants. The corresponding edge theory is the $U(1)/\mathbb{Z}_2$ orbifold, which contains Majorana fermions in its operator content.

cond-mat.str-el↗
arXiv2022

Nonextensive realizations in interacting ion channels: implications for mechano-electrical transducer mechanisms

Although there are theoretical studies on the thermodynamics of ion channels, an investigation involving the thermodynamics of coupled channels has not been proposed. To overcome this issue, we developed calculations to present a thermodynamic scenario associated with mechanoelectrical transduction channels as a single and coupling of two-state channels. The modeling was inspired by the Tsallis theory, in which we derived the open and closed probability distributions, the joint probability distribution, the Tsallis entropy, and the Shannon mutual information. Despite being well studied in many biological systems, the literature has not addressed both entropy and mutual information related to isolated and a pair of physically interacting mechanoelectrical transduction channels. Inspired by the hair cell biophysics, we revealed how the presence of nonextensivity modulates the degree of entropy and mutual information as a function of stereocilia displacements. In this sense, we showed how the non-extensivity regulates the current versus displacement curve for a single and two interacting channels made up of a single open and closed states. Overall, subadditivity and superadditivity yielded increments and decrements in the entropy and mutual information compared with the extensive regime. We also observed that the magnitude of the interaction between the two channels significantly influences the amplitude of the joint entropy and the mutual information. These results are directly related to the modulation of the channel kinetics, given by changes evoked by hair cell displacements. Finally, we found that the gating force modulates the contribution of subadditivity and superadditivity present in the joint entropy and the mutual information. The present findings shed light on the thermodynamic process involved in the molecular mechanisms of the auditory system.

physics.bio-ph↗
arXiv2021

Gravitational corrections to two-loop beta function in quantum electrodynamics

In this work, we use the framework of effective field theory to couple Einstein's gravity to quantum electrodynamics (QED) and determine the gravitational corrections to the two-loop beta function of the electric charge in arbitrary electrodynamics (Lorentz-like) and arbitrary (de Donder like) gravitational gauges. Our results indicate that gravitational corrections do not alter the running behavior of the electric charge; on the contrary, we observe that it gives a positive contribution to the beta function, making the electric charge grow even faster.

hep-th↗
arXiv2020

On the validation of Newcomb-Benford law and Weibull distribution in neuromuscular transmission

The neuromuscular junction represents a relevant substrate for revealing important biophysical mechanisms of synaptic transmission. In this context, calcium ions are important in the synapse machinery, providing the nervous impulse transmission to the muscle fiber. In this work, we carefully investigated whether intervals of spontaneous electrical activity, recorded in seven different calcium concentrations, conform Newcomb-Benford law. Our analysis revealed that electrical discharge of neuromuscular junction obeys the expected values for Newcomb-Benford law for first and second digits, while first-two digits do not perfectly follows the law. We next examined previous theoretical studies, establishing a relation between the law and lognormal and Weibull distributions. We showed that Weibull distribution is more appropriate to fit the intervals as compared to lognormal distribution. Altogether, the present findings strongly suggest that spontaneous activity is a base-scale invariant phenomenon.

q-bio.SC↗
arXiv2020

1/N Expansion for Horava-Lifshitz like four-fermion models

We study a class of four-fermion Gross-Neveu like models in four dimensions with critical exponents $z=2$ and $z=3$. The models with $z=2$ are known to be perturbatively nonrenormalizable but are shown to be renormalizable in the context of the $1/N$ expansion. We calculate explicitly the effective potential for these models.

hep-th↗
arXiv2018

Soft supersymmetry breaking in the nonlinear sigma model

In this work we discuss the dynamical generation of mass in a deformed ${\cal N}=1$ supersymmetric nonlinear sigma model in a two-dimensional ($D=1+1$) space-time. We introduce the deformation by imposing a constraint that softly breaks supersymmetry. Through the tadpole method, we compute the effective potential at leading order in $1/N$ expansion showing that the model exhibit a dynamical generation of mass to the matter fields. Supersymmetry is recovered in the limit of the deformation parameter going to zero.

hep-th↗
arXiv2018

One-loop corrections in the z=3 Lifshitz extension of QED

In this work we study a z=3 Horava-Lifshitz-like extension of QED in (3+1) dimensions. We calculate the one-loop radiative corrections to the two and three-point functions of the gauge and fermion fields. Such corrections were achieved using the perturbative approach and a dimensional regularization was performed only in the spatial sector. Renormalization was required to eliminate the divergent contributions emergent from the photon and electron self-energies and from the three-point function. We verify that the one-loop vertex functions satisfy the usual Ward identities and using renormalization group methods we show that the model is asymptotically free.

hep-th↗
arXiv2017

An UV Completion of Five Dimensional Scalar QED and Lorentz Symmetry

We study a five dimensional Horava-Lifshitz like scalar QED with dynamical exponent z=2. Consistency of the renormalization procedure requires the presence of four quartic and one six-fold scalar couplings besides the terms bilinear in the scalar fields. We compute one-loop radiative corrections to the parameters in the original Lagrangian employing dimensional regularization in the spacial part of the Feynman integrals and prove the relevant Ward identities. By using renormalization group methods, we determine the behavior of the coupling constants with changes in the energy and discuss the emergence of Lorentz symmetry at low energies.

hep-th↗
arXiv2017

Statistical crossover and nonextensive behavior of the neuronal short-term depression

The theoretical basis of neuronal coding, associated with short term degradation in synaptic transmission, is a matter of debate in the literature. In fact, electrophysiological signals are commonly characterized as inversely proportional to stimulus intensity. Among theoretical descriptions of this phenomenon, models based on $1/f$-dependency are employed to investigate the biophysical properties of the short term synaptic depression. In this work we formulated a model based on a paradigmatic \textit{q}-differential equation to obtain a generalized formalism useful for investigation of nonextensivity in this specific type of synaptic plasticity. Our analysis reveals nonextensivity in data from electrophysiological recordings and also a statistical crossover in neurotransmission. In particular, statistical transitions providesadditional support to the hypothesis of heterogeneous release probability of neurotransmitters. On the other hand, the simple vesicle model agrees with data only at low frequency stimulations. Thus, the present work presents a method to demonstrate that short-term depression is not only governed by random mechanisms but also by a nonextensive behavior. Our findings also conciliate morphological and electrophysiological investigations into a coherent biophysical scenario.

q-bio.NC↗
arXiv2017

Aqueous solution interactions with sex hormone-binding globulin and estradiol: A theoretical investigation

Sex hormone-binding globulin (SHBG) is a binding protein that regulates availability of steroids hormones in the plasma. Although best known as steroid carrier, studies have associated SHBG in modulating behavioral aspects related to sexual receptivity. Among steroids, estradiol (17\b{eta}-estradiol, oestradiol or E2) is well recognized as the most active endogenous female hormone, exerting important roles in reproductive and nonreproductive functions. Thus, in this study we aimed to employ molecular dynamics (MD) and docking techniques for quantifying the interaction energy between a complex aqueous solution, composed by different salts, SHBG and E2. Due to glucose concentration resembles those observed in diabetic levels, special emphasis was devoted to uncover the main consequences of this carbohydrate on the SHBG and E2 molecules. We also examined possible energetic changes due to solution on the binding energy of SHBG-E2 complex. In this framework, our calculations uncovered a remarkable interaction energy between glucose and SHBG surface. Surprisingly, we also observed solute components movement toward SHBG yielding clusters surrounding the protein. This finding, corroborated by the higher energy and shorter distance found between glucose and SHBG, suggests a scenario in favor of a detainment state. In addition, in spite of protein superficial area increment it does not exerted modification on binding site area nor over binding energy SHBG-E2 complex. Finally, our calculations also highlighted an interaction between E2 and glucose when the hormone was immersed in the solution. In summary, our findings contribute for a better comprehension of both SHBG and E2 interplay with aqueous solution components.

q-bio.BM↗
arXiv2016

Effective field theory of quantum gravity coupled to scalar electrodynamics

In this work we use the framework of effective field theory to couple Einstein's gravity to scalar electrodynamics and determine the renormalization of the model through the study of physical processes below Planck scale, a realm where quantum mechanics and general relativity are perfectly compatible. We consider the effective field theory up to dimension six operators, corresponding to processes involving one graviton exchange. Studying the renormalization group functions we see that the beta function of the electric charge is positive and possesses no contribution coming from gravitational interaction. Our result indicates that gravitational corrections do not alter the running behavior of the gauge coupling constants, even if massive particles are present.

hep-th↗
arXiv2016

Remarks on a Lorentz-breaking 4D chiral gauge theory

We investigate a Lorentz-violating chiral model composed by two fermions, a complex scalar field and a gauge field. We show that by convenientely adjusting the parameters of the model, it is possible to generate an unambiguous Carroll-Field-Jackiw term and, at the same time, provide the cancelation of the chiral anomaly. The renormalizability of the model is investigated and it is shown that the same counterterms needed in the symmetric phase also renormalize the model with broken symmetry.

hep-th↗
arXiv2015

On one-loop corrections in the Horava-Lifshitz-like QED

We study the one-loop two point functions of the gauge, scalar and spinor fields for a Horava-Lifshitz-like QED with critical exponent $z=2$. It turns out that, in certain cases, the dynamical restoration of the Lorentz symmetry at low energies can take place. We also analyze the three point vertex function of the gauge and spinor fields and prove that the triangle anomaly identically vanishes in this theory.

hep-th↗