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W. T. Cruz

Publications and source records attributed to W. T. Cruz.

At least 19 recordsLinked to original sources

Softly higher-derivative massive gravity

In this work, we study the higher-derivative massive gravity in $D$-dimensional space-time with the mass term arisen due to a 2-brane embedded in a $4D$ Minkowski spacetime. We consider the effect of a resonance mass term from the DGP braneworld model for the higher-derivative massive gravity. Moreover, we add the gravitational Chern-Simons and Ricci-Cotton terms to this model and evaluate the graviton propagator using a basis of Barnes-Rivers spin projectors. Using the obtained propagator, we proceed with discussing the consistency of the model, writing the dispersion relations, and analyzing causality and unitarity.

hep-th

Torsion braneworlds in a tensor-vector gravity

We study the properties of gravity and bulk fields living in a torsion warped braneworld. The torsion is driven by a background vector whose norm provides a source for the bulk cosmological constant. For a vector as the derivative of a scalar field, we find new isotropic and anisotropic thick brane geometries. We analyse the features of bosonic and fermionic fields in this isotropic and in standing wave scenarios. The background vector provides nonminimal coupling between the field and the geometry leading to modifications in the Kaluza-Klein states. The spinor connection is modified by the torsion and a derivative Yukawa-like coupling is proposed. The effects of these new couplings are investigated.

gr-qc

Configurational entropy and Newton's Law in double sine-Gordon braneworlds

In this work, we evaluate the Shannon-like entropic measure of spatially-localized functions for a five-dimensional braneworld generated by a double sine-Gordon (DSG) potential. The differential configurational entropy (DCE) has been shown in several recent works to be a configurational informational measure (CIM) that selects critical points and brings out phase transitions in confined energy models with arbitrary parameters. We select the DSG scenario because it presents an energy-degenerate spatially localized profile where the solutions to the scalar field demonstrate critical behavior that is only a result of geometrical effects. As we will show, the DCE evaluation provides a method for predicting the existence of a transition between the phases of the domain wall solutions. Moreover, the entropic measure reveals information about the model that is capable of describing the phase sector where we obtain resonance modes on the massive spectra of the graviton. The graviton resonance lifetimes are related to the existence of scales on which 4D gravity is recovered. Thus, we correlate the critical points defined by the {CIMs} with the existence of resonances and their lifetimes. To extend our research regarding this system, we calculate the corrections to Newton's Law coming from the graviton modes.

gr-qc

Construction of a Model of the Solar System with Temperature Control for Visually Impaired Students

In this work, we present a study carried out to develop a didactic kit based on the use of touch and thermal receivers for the teaching of Astronomy. The proposal arose in the face of the difficulties encountered in the search for experiments capable of presenting the best concepts involved in the teaching of Astronomy for visually impaired people. The equipment consists of the use of a model with hemispheres with Peltier pellets for simulation of temperature scale of planets of the Solar System. The research was based on the use of accessible and low-cost materials. All the materials used and the assembly of the equipment are described in this work, since the design until the application of the final product for students. This experiment was part of a set of pedagogical equipment presented at a scientific exhibition for the visually impaired during the 15 a National Science and Technology Week in the city of Juazeiro do Norte in the State of Ceará.

physics.ed-ph

Antisymmetric tensor propagator with spontaneous Lorentz violation

In this work, we study the spontaneous Lorentz symmetry breaking due to an antisymmetric 2-tensor field in Minkowski spacetime. For a smooth quadratic potential, the spectrum of the theory exhibits massless and massive excitations. We show that the equations of motion for the free field obey some constraints which lead to the massive mode be non-propagating at leading order. Besides, there exists a massless mode in the theory which can be identified with the usual Kalb-Ramond field, carrying only one on-shell degree of freedom. The same conclusion holds when one analyses the pole structure of its Feynman propagator. A new complete set of spin-type operators is found, which was the requirement to evaluate the propagator of the Kalb-Ramond field modified by the presence of a nonzero vacuum expectation value responsible for the Lorentz violation.

hep-th

Geometric standing wave braneworld and field localization in Lyra manifold

In this work, we propose a standing wave braneworld based on Lyra geometry scenario. The Lyra displacement vector provides a modification in Einstein equations which can be interpreted as a noninteracting phantom scalar. From the Einstein's equation in Lyra manifold, a 5D standing wave braneworld is constructed in the presence of a cosmological constant. Unlike other standing wave solutions presented in the literature, no matter field is necessary to obtain these new solutions. We analyze the properties of the scalar, gauge vector and fermionic fields in this model, highlighting the relevance of geometric structure in the process of trapping matter.

gr-qc

Configurational Entropy as a tool to select a physical Thick Brane Model

We analise braneworld scenarios via a configurational entropy (CE) formalism. Braneworld scenarios have drawn attention mainly due to the fact that they can explain the hierarchy problem and unify the fundamental forces through a symmetry breaking procedure. Those scenarios localize matter in a $(3+1)$ hypersurface, the brane, which is inserted in a higher dimensional space, the bulk. Novel analytical braneworld models, {in which the warp factor depends} on a free parameter $n$, were recently released in the literature. In this article we will provide a way to constrain this parameter through the relation between information and dynamics of a system described by the CE. We demonstrate that in some cases the CE is an important tool in order to provide the most probable physical system among all the possibilities. In addition, we show that the highest CE is correlated to a tachyonic sector of the configuration, where the solutions for the corresponding model are dynamically unstable.

hep-th

Phase transitions in thick branes endorsed by entropic information

The so-called configurational entropy (CE) framework has proved to be an efficient instrument to study nonlinear scalar field models featuring solutions with spatially-localized energy, since its proposal by Gleiser and Stamapoulos. Therefore, in this work, we apply this new physical quantity in order to investigate the properties of degenerate Bloch branes. We show that it is possible to construct a configurational entropy measure in functional space from the field configurations, where a complete set of exact solutions for the model studied displays both double and single-kink configurations. Our study shows a rich internal structure of the configurations, where we observe that the field configurations undergo a quick phase transition, which is endorsed by information entropy. Furthermore, the Bloch configurational entropy is employed to demonstrate a high organisational degree in the structure of the configurations of the system, stating that there is a best ordering for the solutions.

hep-th

Analytical model of atomic-force-microscopy force curves in viscoelastic materials exhibiting power law relaxation

We propose an analytical model for the force-indentation relationship in viscoelastic materials exhibiting a power law relaxation described by an exponent n, where n = 1 represents the standard viscoelastic solid (SLS) model, and n < 1 represents a fractional SLS model. To validate the model, we perform nanoindentation measurements of poylacrylamide gels with atomic force microscopy (AFM) force curves. We found exponents n < 1 that depends on the bysacrylamide concentration. We also demonstrate that the fitting of AFM force curves for varying load speeds can reproduce the dynamic viscoelastic properties of those gels measured with dynamic force modulation methods.

cond-mat.soft

Multiresonance modes in sine-Gordon brane models

In this work, we study the localization of the vector gauge field in two five-dimensional braneworlds generated by scalar fields coupled to gravity. The sine-Gordon like potentials are employed to produce different thick brane setups. A zero mode localized is obtained, and we show the existence of reverberations with the wave solutions indicating a quasi-localized massive mode. More interesting results are achieved when we propose a double sine-Gordon potential to the scalar field. The resulting thick brane shows a more detailed topology with the presence of an internal structure composed by two kinks. The massive spectrum of the gauge field is revalued on this scenario revealing the existence of various resonant modes. Furthermore, we compute the corrections to Coulomb law coming from these massive KK vector modes in these thick scenarios, where is concluded that the dilaton parameter regulates these corrections.

hep-th

Gravity localization on hybrid branes

This work deals with gravity localization on codimension-1 brane worlds engendered by compacton-like kinks, the so-called hybrid branes. In such scenarios, the thin brane behaviour is manifested when the extra dimension is outside the compact domain, where the energy density is non-trivial, instead of asymptotically as in the usual thick brane models. The zero mode is trapped in the brane, as required. The massive modes, although are not localized in the brane, have important phenomenological implications such as corrections to the Newton's law. We study such corrections in the usual thick domain wall and in the hybrid brane scenarios. By means of suitable numerical methods, we attain the mass spectrum for the graviton and the corresponding wavefunctions. The spectra possess the usual linearly increasing behaviour from the Kaluza-Klein theories. Further, we show that the 4D gravitational force is slightly increased at short distances. The first eigenstate contributes highly for the correction to the Newton's law. The subsequent normalized solutions have diminishing contributions. Moreover, we find out that the phenomenology of the hybrid brane is not different from the usual thick domain wall. The use of numerical techniques for solving the equations of the massive modes is useful for matching possible phenomenological measurements in the gravitational law as a probe to warped extra dimensions.

hep-th

Gravity localization in sine-Gordon braneworlds

In this work we study two types of five-dimensional braneworld models given by sine-Gordon potentials. In both scenarios, the thick brane is generated by a real scalar field coupled to gravity. We focus our investigation on the localization of graviton field and the behaviour of the massive spectrum. In particular, we analyse the localization of massive modes by means of a relative probability method in a Quantum Mechanics context. Initially, considering a scalar field sine-Gordon potential, we find a localized state to the graviton at zero mode. However, when we consider a double sine-Gordon potential, the brane structure is changed allowing the existence of massive resonant states. The new results show how the existence of an internal structure can aid in the emergence of massive resonant modes on the brane.

hep-th

Dirac equation in very special relativity for hydrogen atom

In this work, we study the modified Dirac equation in the framework of very special relativity (VSR). The low-energy regime is accessed and the nonrelativistic Hamiltonian is obtained. It turns out that this Hamiltonian is similar to that achieved from the Standard Model Extension (SME) via coupling of the spinor field to a Lorentz-violating term, but new features arise inherited from the non-local character of the VSR. In addition, the implications of the VSR-modified Lorentz symmetry on the spectrum of a hydrogen atom are determined by calculating the first-order energy corrections in the context of standard quantum mechanics. Among the results, we highlight that the modified Hamiltonian provides non-vanishing corrections which lift the degeneracy of the energy levels and allow us to find an upper bound upon the VSR-parameter.

hep-th

Gravitational Kaluza-Klein modes in the String-Cigar Braneworld

In this work the gravitational Kaluza-Klein (KK) modes are analysed on string-like braneworlds in six dimensions, namely the thin string-like Gherghetta-Shaposhnikov (GS) and the thick string-cigar model. We find a new massless mode in both modes satisfying the respective Schroedinger equation. By means of numerical analysis for both models, a complete graviton spectrum and eigenfunctions is attained. Besides the linear regime, the KK spectrum exhibits a decreasing behavior with an asymmetric mass gap with respect to the massless mode. The discontinuity is bigger in the GS model, and it is invariant upon the geometrical flow. A massive mode is obtained in the GS model with a tiny mass which does not match in any regime. It turns out that in the string-cigar model, the core brane structure smoothes and amplifies the KK modes near the brane. Further, the presence of a potential well allows the existence of resonant massive gravitons for small masses in the string-cigar scenario.

hep-th

Graviton resonances on two-field thick branes

This work presents new results about the graviton massive spectrum in two-field thick branes. Analyzing the massive spectra with a relative probability method we have firstly showed the presence of resonance structures and obtained a connection between the thickness of the defect and the lifetimes of such resonances. We obtain another interesting results considering the degenerate Bloch brane solutions. In these thick brane models, we have the emergence of a splitting effect controlled by a degeneracy parameter. When the degeneracy constant tends to a critical value, we have found massive resonances to the gravitational field indicating the existence of modes highly coupled to the brane. We also discussed the influence of the brane splitting effect over the resonance lifetimes.

hep-th

A 6D standing-wave Braneworld with normal matter as source

A six dimensional standing-wave braneworld model has been constructed. It consists in an anisotropic 4-brane generated by standing gravitational waves whose source is normal matter. In this model the compact (on-brane) dimension is assumed to be sufficiently small in order to describe our universe (hybrid compactification). The bulk geometry is non-static, unlike most of the braneworld models in the literature. The principal feature of this model is the fact that the source is not a phantom like scalar field, as the original standing-wave model that was proposed in five dimensions and its six dimensional extension recently proposed in the literature. Here it was obtained a solution in the presence of normal matter what assures that the model is stable. Also our model is the first standing wave brane model in the literature which can be applied successfully to the hierarchy problem. Additionally, we have shown that the zero-mode for the scalar and fermionic fields are localized around the brane. Particularly for the scalar field we show that it is localized on the brane, regardless the warp factor is decreasing or increasing. This is in contrast to the case of the local string-like defect where the scalar field is localized for a decreasing warp factor only.

hep-th

Kalb-Ramond field localization on the Bloch brane

This work deals with new results on the Kalb-Ramond (KR) field localization in braneworld models. We consider a five-dimensional warped spacetime with an embedded 4D thick brane which is generated by two real scalar fields coupled with gravity (the so called Bloch brane). We find a KR field zero mode localized with the inclusion of the dilaton coupling. Analyzing the massive spectrum, we detected a series of resonant modes that arise from the solutions of the Schrödinger-like equation for KR field. The effects of the brane thickness and of the dilaton coupling over the resonance structures are determined. Such analysis is extended to the resonance lifetimes of the massive modes, allowing a better understanding on the localization mechanism of the model.

hep-th

Matter-gravity scattering in the presence of spontaneous Lorentz violation

Considering quantum gravity within the framework of effective field theory, we investigated the consequences of spontaneous Lorentz violation for the gravitational potential. In particular, we focus our attention on the bumblebee models, in which the graviton couples to a vector $B_μ$ that assumes a nonzero vacuum expectation value. The leading order corrections for the nonrelativistic potential are obtained from calculation of the scattering matrix of two scalar particles interacting gravitationally. These corrections imply anisotropic properties associated with the bumblebee background and also add a Darwin-like term for Newton's potential.

hep-th