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M. O. Tahim

Publications and source records attributed to M. O. Tahim.

At least 19 recordsLinked to original sources
arXiv2026

Mass for Particles from Extra Dimensions

We investigate a geometric mechanism for mass generation in a codimension-two hedgehog braneworld. A massless particle propagating in the bulk acquires an effective four-dimensional mass through its motion along the compact angular extra dimension, yielding a dynamically determined Kaluza-Klein spectrum after canonical quantization. While the bosonic sector exhibits no radial confinement, extending the analysis to N = 1, 2 spinning-particle models shows that the spin-curvature coupling modifies the effective potential and introduces a level-dependent localization pattern for the Kaluza-Klein modes. The results establish a particle-mechanics realization of geometric mass generation in flux-supported codimension-two braneworlds and highlight the interplay between bulk geometry, spin, and the effective four-dimensional mass spectrum.

hep-th↗
arXiv2026

Traversable double-throat wormholes in a string cloud background

This work constructs a new class of traversable wormhole solutions with a double-throat topology, modeled as a localized perturbation of the Ellis-Bronnikov metric in a string cloud background. Embedding diagrams and the analysis of curvature invariants, including the Kretschmann scalar and the Weyl invariant, illustrate the geometric transition from single to double-throat structures as a function of the perturbation amplitude. By imposing the zero-tidal condition, we derive analytical expressions for the energy density and pressures, showing an asymptotic $r^{-2}$ decay characteristic of a string cloud, endowed with the topology of a global monopole. A key finding is that the energy density converges to a positive constant at the center, with the radial pressure becoming negative. This local behavior provides the repulsive support necessary to inflate the inter-throat region with non-exotic matter, concentrating Null Energy Condition violations to the throat vicinities. These results suggest that multi-throat geometries offer a natural mechanism for localizing exotic matter while maintaining a physical asymptotic background.

gr-qc↗
arXiv2026

Particle and Superparticle Confinement in Higher Codimension Braneworlds

In this work we analyze the classical confinement of relativistic and supersymmetric spinning particles in higher-codimension braneworlds. Considering warped backgrounds generated by string-like $ n=2$ and global scalar defects $ n \geq 3$, we derive the effective radial dynamics from a Polyakov-type action. For spinless particles, the effective potential is monotonically decreasing, leading to repulsive behavior and the absence of confinement. In contrast, for $N=1,2 $ spinning particles, spin-curvature coupling modifies the potential, allowing the emergence of stable equilibrium points. Depending on the coupling parameter, particles may be confined on the membrane or in nearby regions, exhibiting bounded or satellite-like motion. These results emphasize the role of spin in localization mechanisms.

hep-th↗
arXiv2025

A Satellite $N=2$ Superparticle in Extra Dimensions

In this work we discuss the issue of localization of $N=2$ spinning particles. More specifically, we show that we can not confine the spinning particle within the Randall-Sundrum scenario. We argue that this result directly affects studies related to localization of $p$-form fields. We show that, due to the non confinement of the superparticle, we can not localize $p$-forms on the membrane.

hep-th↗
arXiv2025

Coupled Oscillators, Frequency Transfer and the Higgs Mechanism's Teaching

In this work, we propose a simple model to teach the Higgs mechanism of spontaneous symmetry breaking in particle physics. The basic idea is associated with the analysis of two particles' motion subjected to specific potentials that, in certain situations, will reproduce oscillatory motions with a frequency transfer effect.

physics.ed-ph↗
arXiv2022

Non-Integrability of Strings in $AdS_{6}\times S^{2}\timesΣ$ Background and its 5D Holographic Duals

In this manuscript we study Liouvillian non-integrability of strings in $AdS_{6}\times S^{2}\timesΣ$ background. We consider soliton strings and look for simple solutions in order to reduce the equations to only one linear second order differential equation called Normal Variation Equation (NVE). We study truncations in $η$ and $σ$ variables showing their applicability or not to catch (non) integrability of models. With this technique we are able to study many recent cases considered in the literature: the abelian and non-abelian T-duals, the $(p,q)$-5-brane system, the T$_{N}$, $+_{MN}$ theories and the $\tilde{T}_{N,P}$ and $+_{P,N}$ quivers. We show that all of them are not integrable. Finally, we consider the general case at the boundary $σ=σ_0$ for large $σ_0$ and show that we can get general conclusions about integrability. For example, beyond the above quivers, we show generically that long quivers are not integrable. In order to establish the results, we numerically study the string dynamical system seeking by chaotic behaviour. Such a characteristic gives one more piece of evidence for non-integrability of the background studied.

hep-th↗
arXiv2019

Localization of a Model With U(1) Kinetic Gauge Mixing

In this paper we study the localization of a model with kinetic gauge mixing on a thin membrane. The model we discuss is a theory for millicharged particles, proposed by Holdom in 1985, and that now is object of study in the LHC. We propose a geometrical coupling between the gauge fields, the Ricci scalar and the Ricci tensor. We show that it is possible to localize such a model by regarding specific values for the coupling constants. We find the solutions for the two gauge fields and discuss the localization for scalar fields that appears naturally in the process. We show that not necessarily the gauge and scalar fields are localized at the same time.

hep-th↗
arXiv2018

Quantum Vacuum Fluctuations in a Chromomagnetic-like Background

In this paper we study the effects associated to quantum vacuum fluctuations of vectorial perturbations of the Abelian SU(2) Yang-Mills field in a static and homogeneous chromomagnetic-like background field, at zero temperature. We use periodic and antiperiodic boundary conditions in order to calculate the Casimir energy by means of the frequency sum technique and of the regularization method based on zeta functions, analyzing its behavior in the weak and strong coupling regimes. We compare the obtained results with the similar ones found for scalar and spinor fields placed in an ordinary magnetic field background. We show that only in the weak coupling regime the non-trivial topology of the system encoded in the antiperiodic boundary conditions changes the nature of the Casimir force with respect to the periodic ones. Considering the weak coupling scenario, we show that the introduction of a third polarization state in the perturbations makes manifest the effects on the Casimir energy due to the coupling with the chromomagnetic-like background field, for both the boundary conditions. Finally, in the strong coupling regime, in which the quantum vacuum is not stable due to the Nielsen-Olesen instabilities, we evaluate the effects of a compact extra dimension on its stabilization.

hep-th↗
arXiv2018

Comment on "Quantizing strings in de Sitter space"

Trying to quantize the string in a de Sitter spacetime, Miao Li, Wei Song and Yushu Song presents a solution for the string equation of motion (JHEP04(2007)042) that is not correct. This reopens the problem by them addressed.

hep-th↗
arXiv2017

On the Global Casimir Effect in the Schwarzschild Spacetime

In this paper we study the vacuum quantum fluctuations of the stationary modes of an uncharged scalar field with mass $m$ around a Schwarzschild black hole with mass $M$, at zero and non-zero temperatures. The procedure consists of calculating the energy eigenvalues starting from the exact solutions found for the dynamics of the scalar field, considering a frequency cutoff in which the particle is not absorbed by the black hole. From this result, we obtain the exterior contributions for the vacuum energy associated to the stationary states of the scalar field, by considering the half-summing of the levels of energy and taking into account the respective degeneracies, in order to better capture the nontrivial topology of the black hole spacetime. Then we use the Riemann's zeta function to regularize the vacuum energy thus found. Such a regularized quantity is the Casimir energy, whose analytic computation we show to yield a convergent series. The Casimir energy obtained does not take into account any boundaries artificially imposed on the system, just the nontrivial spacetime topology associated to the source and its singularity. We suggest that this latter manifests itself through the vacuum tension calculated on the event horizon. We also investigate the problem by considering the thermal corrections via Helmholtz free energy calculation, computing the Casimir internal energy, the corresponding tension on the event horizon, the Casimir entropy, and the thermal capacity of the regularized quantum vacuum, analyzing their behavior at low and high temperatures, pointing out the thermodynamic instability of the system in the considered regime, i.e., $mM\ll 1$.

gr-qc↗
arXiv2017

Thermal Casimir effect in Kerr spacetime with quintessence and massive gravitons

Starting from an analytical expression for the Helmholtz free energy we calculate the thermal corrections to the Casimir energy-density and entropy within nearby ideal parallel plates in the vacuum of a massless scalar field. Our framework is the Kerr spacetime in the presence of quintessence and massive gravitons. The high and low temperature regimes are especially analysed in order to distinguish the main contributions. For instance, in the high temperature regime, we show that the force between the plates is repulsive and grows with both the quintessence and the massive gravitons. Regarding the Casimir entropy, our results are in agreement with the Nernst heat theorem and therefore confirm the third law of thermodynamics in the present scenario.

gr-qc↗
arXiv2016

Variations in the fine structure constant constraining gravity theories

In this paper, we investigate how the fine structure constant, $α$, locally varies in the presence of a static and spherically symmetric gravitational source. The procedure consists in calculating the solution and the energy eigenvalues of a massive scalar field around that source, considering the weak-field regimen. From this result, we obtain expressions for an spatially variable fine structure constant by considering suitable modifications in the involved parameters admitting some scenarios of semi-classical and quantum gravities. Constraints on free parameters of the approached theories are calculated from astrophysical observations of the emission spectra of a white dwarf. Such constraints are finally compared with those ones obtained in the literature.

gr-qc↗
arXiv2015

Vacuum polarization at the boundary of a topological insulator

In this paper we study the polarized vacuum energy on the conducting surface of a topological insulator characterized by both $Z_2$ topological index and time reversal symmetry. This boundary is subject to the action of a static and spatially homogeneous magnetic field perpendicular to it as well as of an electric field that is uniform near the considered surface and produced by a biased voltage, at zero temperature. To do this, we consider modifications in the Gauss law that arise due to the nonzero gradient of the axionlike pseudoscalar factor coupled to the applied magnetic field, which accounts for the topological properties of the system. Such a term allows us to find a correction to the induced charges which modifies the quantum vacuum of the spinor field regarding an ordinary surface. The polarized vacuum energy is calculated in both the weak-field approximation and in the general case, and since the found energy depends on a length defined on the boundary, we show that there is a radial density of force or a surface shear stress that tends to shrink it.

hep-th↗
arXiv2014

Gauge Field Emergence from Kalb-Ramond Localization

A new mechanism, valid for any smooth version of the Randall-Sundrum model, of getting localized massless vector field on the brane is described here. This is obtained by dimensional reduction of a five dimension massive two form, or Kalb-Ramond field, giving a Kalb-Ramond and an emergent vector field in four dimensions. A geometrical coupling with the Ricci scalar is proposed and the coupling constant is fixed such that the components of the fields are localized. The solution is obtained by decomposing the fields in transversal and longitudinal parts and showing that this give decoupled equations of motion for the transverse vector and KR fields in four dimensions. We also prove some identities satisfied by the transverse components of the fields. With this is possible to fix the coupling constant in a way that a localized zero mode for both components on the brane is obtained. Then, all the above results are generalized to the massive $p-$form field. It is also shown that in general an effective $p$ and $(p-1)-$forms can not be localized on the brane and we have to sort one of them to localize. Therefore, we can not have a vector and a scalar field localized by dimensional reduction of the five dimensional vector field. In fact we find the expression $p=(d-1)/2$ which determines what forms will give rise to both fields localized. For $D=5$, as expected, this is valid only for the KR field.

hep-th↗
arXiv2014

Gauge Field Localization on the Brane Through Geometrical Coupling

In this paper we consider a geometrical Yukawa coupling as a solution to the problem of gauge field localization. We show that upon dimensional reduction the vector field component of the field is localized but the scalar component ($A_5$) is not. We show this for any smooth version of the Randall-Sundrum model. The covariant version of the model with geometrical coupling simplify the generalization to smooth versions generated by topological defects. This kind of model has been considered some time ago, but there it has been introduced two free parameters in order to get a localized solution which satisfy the boundary conditions: a mass term in five dimensions and a coupling with the brane. The boundary condition fix one of them and the model is left with one free parameter $M$. First we show that by considering a Yukawa coupling with the Ricci scalar it is possible to unify these two parameter in just one fixed by the boundary condition. With this we get a consistent model with no free parameters and the mass term can be interpreted as a coupling to the cosmological constant.

hep-th↗
arXiv2014

New Analytical Solutions for Bosonic Field Trapping in Thick Branes

New analytical solutions for gravity, scalar and vector field localization in Randall-Sundrum(RS) models are found. A smooth version of the warp factor with an associated function $f(z)=\exp(3A(z)/2)$ inside the walls ($|z|<d$) is defined, leading to an associated equation and physical constraints on the continuity and smoothness of the background resulting in a new space of analytical solutions. We solve this associated equation analytically for the parabolic and Pöschl-Teller potentials and analyze the spectrum of resonances for these fields. By using the boundary conditions we are able to show that, for any of these solutions, the density probability for finding a massive mode in the membrane has a universal behavior for small values of mass given by $|ψ_m(0)|^2=β_1m+β_3m^3+β_L m^3\log(m)+\cdots$. As a consequence, the form of the leading order correction, for example, to the Newton's law is general and does not depend on the potential used. At the end we also discuss why complications arises when we try to use the method to find analytical solutions to the fermion case.

hep-th↗
arXiv2013

Bosonic Fields in Crystal Manyfolds

A chain-like or a 1D crystal-like universe made of intersecting membranes in extra dimensions in a Randall-Sundrum scenario is studied. A background gravitational metric satisfying the right boundary conditions is considered to study the localization of the scalar, gauge and Kalb-Ramond field. It is found that the wave function for the fields are Bloch waves. The mass modes equations are calculated allowing us to show the zero-gap mass behavior and the mass dispersion relation for each field. Finally we generalize all these results and consider $q-$forms in the crystal membrane universe. We show that, depending to the dimension $D$, the form $q$ and the dilation coupling $λ$ the mass spectrum can be the same for the different bosonic field studied.

hep-th↗