arXiv subjects

G. Alencar

Publications and source records attributed to G. Alencar.

At least 109 records · Page 6Linked to original sources

arXiv2015

Massive $p$-form trapping as a $p$-form on a brane

It is shown here that the zero mode of any form field can be trapped to the brane using the model proposed by Ghoroku and Nakamura. We start proven that the equations of motion can be obtained without splitting the field in even and odd parts. The massive and tachyonic cases are studied revealing that this mechanism only traps the zero mode. The result is then generalized to thick branes. In this scenario, the use of a delta like interaction of the quadratic term is necessary leading to a "mixed" potential with singular and smooth contributions. It is also shown that all forms produces an effective theory in the brane without gauge fixing. The existence of resonances with the transfer matrix method is then discussed. With this we analyze the resonances and look for peaks indicating the existence of unstable modes. Curiously no resonances are found in opposition of other models in the literature. Finally we find analytical solutions for arbitrary $p-$forms when a specific kind of smooth scenario is considered.

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

Solutions to the problem of ELKO spinor localization in brane models

In this paper we present two different solutions to the problem of zero mode localization of ELKO spinor. In a recent paper the present authors reopened this problem since the solution presented before did not satisfy the boundary condition at the origin. The first solution is given by the introduction of a mass term and by coupling the spinor with the brane through a delta function. The second solution is reached by a Yukawa geometrical coupling with the Ricci scalar. This two models changes consistently the the boundary condition at infinity and at the origin. For the case of Geometrical coupling we are able to show that the zero mode is localized for any smooth version of the RS model.

hep-th↗

arXiv2014

Comment on "Localization of 5D Elko Spinors on Minkowski Branes"

We show that the statement in Yu-Xiao Liu, Xiang-Nan Zhou, Ke Yang and Feng-Wei Chen [Phys. Rev. D 86 , 064012 (2012)] that the zero mode of ELKO spinor is localized in some thin brane scenarios is not correct. This reopens the problem of localization of ELKO spinors.

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

Construction of Multiple Spherical Branes Cosmological Scenario

The general solution of Einstein's gravity equation in $D$ dimensions for an anisotropic and spherically symmetric matter distribution is calculated in a bulk with position dependent cosmological constant. Results for $n$ concentric $(D-2)-$branes with arbitrary mass, radius and pressure with different cosmological constant between branes are found. It is shown how the difference between the cosmological constant contributes to the effective mass of each brane, and it is also shown that the equation of state for each brane influences the dynamics of branes, which can be divided into eras according to the dominant matter. This scenario can be used to model the universe in the D=5 case, which may presents a richer phenomenology than the current models. The evolution law of the branes is studied, and the anisotropic pressure that remove divergences is found. The Randall-Sundrum metric in an outside region in the flat branes limit is also derived.

gr-qc↗

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↗

arXiv2013

Cosmologies of Multiple Spherical Brane-universe Model

The Friedmann-Robertson-Walker metric with spherical topology is calculated as an effective metric at the brane in a multiple branes in $D-$dimensional spacetime scenario. In this model the radius of the brane is the cosmological scale factor, and its evolution is calculated from the viewpoint of the observers on their respective branes. The cosmology of the brane-universe is analyzed in cases where the anisotropic pressure has a cosmological constant like state equation. The pressure values needed to distinguish the oscillating, expanding or collapsing solutions are found, and the minimum value of a brane-universe mass to prevent a collapse into a black hole is also calculated. Finally the equation of motion is solved numerically in order to illustrate the different cosmological scenarios and to validate the analytical results.

gr-qc↗

arXiv2012

Quantum Kalb-Ramond Field in D-dimensional de Sitter Spacetimes

In this work we investigate the quantum theory of the Kalb-Ramond fields propagating in $D-$dimensional de Sitter spacetimes using the dynamic invariant method developed by Lewis and Riesenfeld [J. Math. Phys. 10, 1458 (1969)] to obtain the solution of the time-dependent Schrödinger equation. The wave function is written in terms of a $c-$number quantity satisfying of the Milne-Pinney equation, whose solution can be expressed in terms of two independent solutions of the respective equation of motion. We obtain the exact solution for the quantum Kalb-Ramond field in the de Sitter background and discuss its relation with the Cremmer-Scherk-Kalb-Ramond model.

hep-th↗

arXiv2012

A Transfer Matrix Method for Resonances in Randall-Sundrum Models III: An analytical comparison

The transfer matrix method is used to analyze resonances in Randall-Sundrum models. Although it has successfully been used previously by us we provide here a comparison between the numerical and analytical models. To reach this we first find new exact solution for the scalar, gauge, Kalb-Ramond and $q-$form fields. Them we calculate numerically the resonances by the transfer matrix method and compare with the analytical result. For completeness, this is done for models with and without the dilaton coupling. The results show a perfect agreement between the analytical and numerical methods.

hep-th↗

arXiv2012

An Exact Solution to the Quantized Electromagnetic Field in D-dimensional de Sitter Spacetimes

In this work we investigate the quantum theory of light propagating in $D-$dimensional de Sitter spacetimes. To do so, we use the method of dynamic invariants to obtain the solution of the time-dependent Schrödinger equation. The quantum behavior of the electromagnetic field in this background is analyzed. As the electromagnetism loses its conformality in $D\neq4$, we point that there will be particle production and comoving objects will feel a Bunch-Davies thermal bath. This may become important in extra dimension physics and raises the intriguing possibility that precise measurements of the Cosmic Microwave Background could verify the existence of extra dimensions.

hep-th↗

arXiv2012

Morse potential derived from first principles

We show that a direct connection can be drawn, based on fundamental quantum principles, between the Morse potential, extensively used as an empirical description for the atomic interaction in diatomic molecules, and the harmonic potential. This is conceptually achieved here through a non-additive translation operator, whose action leads to a perfect equivalence between the quantum harmonic oscillator in deformed space and the quantum Morse oscillator in regular space. In this way, our theoretical approach provides a distinctive first principle rationale for anharmonicity, therefore revealing a possible quantum origin for several related properties as, for example, the dissociation energy of diatomic molecules and the deformation of cubic metals.

cond-mat.mtrl-sci↗

arXiv2012

Quantum Scalar Field in D-dimensional de Sitter Spacetimes

In this work we investigate the quantum theory of scalar fields propagating in a $D-$dimensional de Sitter spacetime. The method of dynamic invariants is used to obtain the solution of the time-dependent Schrödinger equation. The quantum behavior of the scalar field in this background is analyzed, and the results generalize previous ones found in the literature. We point that the Bunch-Davies thermal bath depends on the choice of $D$ and the conformal parameter $ξ$. This is important in extra dimension physics, as in the Randall-Sundrum model.

hep-th↗

arXiv2011

RNS and Pure Spinors Equivalence for Type I Tree Level Amplitudes Involving up to Four Fermions

In this paper we give a proof of the equivalence between the RNS and Pure Spinor formalism for Type I tree level amplitudes involving up to four fermions. This result have been obtained previously for amplitudes involving only closed or open amplitudes and here we extend it to include Type I amplitudes. For this we first prove the cyclic symmetry of Type I superstring in a way that it is also valid for the Pure Spinor formalism. The technique used is applied to simplify the calculation of the tree level three point amplitude previously computed. As a byproduct, we are able to calculate the gauge anomaly amplitude of type I Superstrings in this formalism.

hep-th↗

arXiv2011

A Transfer Matrix Method for Resonances in Randall-Sundrum Models II: The Deformed Case

Here we consider resonances of the Gauge, Gravity and Spinor fields in Randall-Sundrum-like scenarios. We consider membranes that are generated by a class of topological defects that are deformed domain walls obtained from other previously known ones. They are obtained by a deformation procedure generate different potentials to the associated Schrödinger-like equation. The resonance spectra are calculated numerically using the method of Transfer Matrix developed by the authors and presented in JHEP 1108 (2011) 071. The new deformed defects change the resonances spectra of all fields considered and the associated phenomenology as well.

hep-th↗

arXiv2011

A Transfer Matrix Method for Resonances in Randall-Sundrum Models

In this paper we discuss in detail a numerical method to study resonances in membranes generated by domain walls in Randall-Sundrum-like scenarios. It is based on similar works to understand the quantum mechanics of electrons subject to the potential barriers that exist in heterostructures in semiconductors. This method was used recently to study resonances of a three form field and lately generalized to arbitrary forms. We apply it to a lot of important models, namely those that contain the Gauge, Gravity and Spinor fields. In many cases we find a rich structure of resonances which depends on the parameters involved.

hep-th↗

arXiv2011

Dual Spaces of Resonance In Thick $p-$Branes

In this work we consider $q-$form fields in a $p-$brane embedded in a $D=(p+2)$ space-time. The membrane is generated by a domain wall in a Randall-Sundrum-like scenario. We study conditions for localization of zero modes of these fields. The expression agrees and generalizes the one found for the zero, one, two and three-forms in a $3-$brane. By a generalization we mean that our expression is valid for any form in an arbitrary dimension with codimension one. We also point out that, even without the dilaton coupling, some form fields are localized in the membrane. The massive modes are considered and the resonances are calculated using a numerical method. We find that different spaces have identical resonance structures, which we call dual spaces of resonances(DSR).

hep-th↗