arXiv subjects

O. Santillán

Publications and source records attributed to O. Santillán.

7 recordsLinked to original sources

arXiv2024

About gravitational radiation of semi local strings with non compact internal modes

The present work studies the gravitational radiation of a non abelian vortex with a non compact internal moduli describing its excitations. This situation may be realised by semi-local supersymmetric vortices \cite{novedad1}-\cite{reviewshifman}, although supersymmetry is not necessary for this to happen. In the situation considered along this work, the internal space has infinite volume, and a largely energetic perturbation propagates along the object, even though the vortex line may not be moving. A specific configuration is presented, in which the internal space is the resolved conifold with its Ricci flat metric. The curious feature about it is that it corresponds to a static vortex, that is, the perturbation is only due to the internal modes. Even being static, the emission of gravitational radiation is in the present case of considerable order. This suggest that the presence of slowly moving objects that can emit a large amount of gravitational radiation is a hint of non abelianity.

hep-th↗

arXiv2022

About apparent superluminal drives in generic gravity theories

As is well known, there exists warp drives in GR, such as the Alcubierre bubbles, which achieve an apparent faster than light travel \cite{alcubierre}. A result due to Gao and Wald \cite{gaowald} suggests that such a travel is unlikely for GR with matter satisfying both the Null Energy and the Null Generic Conditions. There exists a generalization of this statement due to Galloway, that ensures that the Gao-Wald result is true regardless the underlying gravity model, unless there exists at least one inextendible null geodesic with achronal image in the space time (a null line). The proof of this proposition is based on techniques of causal theories, and has never been released. In the present work an independent proof of this result is presented by use of the Raychaudhuri equation, and avoiding several technical complications described along the text. Some consequences of these affirmations are discussed at last section, in particular their potential use in problems of causality.

gr-qc↗

arXiv2021

Neutrino emission and initial evolution of axionic quark nuggets

The axion quark nuggets introduced in \cite{zhitnitsky}-\cite{zhitnitsky13} are a candidate for cold dark matter which, in addition, may be relevant in baryogenesis scenarios. The present work studies their evolution till they enter in the colour superconducting phase. This evolution was already considered in \cite{zhitnitsky5}, where it is concluded that a large chemical potential $μ$ is induced on the bulk of the object. The baryon number accumulated at the domain wall surrounding the object is taken as predominant in \cite{zhitnitsky5}, and it is suggested that internal and external fluxes are compensated and can be neglected. In the present work, the possibility that the bulk contribution to the baryon number may be relevant at initial stages and that the object may emit a large amount of neutrinos due to quark-antiquark annihilations is taken into account. The outcome is a more violent contraction of the object and, perhaps, a more effective cooling. Therefore, the resulting objects may have a smaller size. Even taking into account these corrections, it is concluded that the cosmological applications of these objects are not spoiled. These applications are discussed along the text.

hep-ph↗

arXiv2019

About the Cauchy problem in Stelle's quadratic gravity

The focus of the present work is on the Cauchy problem for the quadratic gravity models introduced in \cite{stelle}-\cite{stelle2}. These are renormalizable higher order derivative models of gravity, but at cost of ghostly states propagating in the phase space. A previous work on the subject is \cite{noakes}. The techniques employed here differ slightly from those in \cite{noakes}, but the main conclusions agree. Furthermore, the analysis of the initial value formulation in \cite{noakes} is enlarged and the use of harmonic coordinates is clarified. In particular, it is shown that the initial constraints found \cite{noakes} include a redundant one. In other words, this constraint is satisfied when the equations of motion are taken into account. In addition, some terms that are not specified in \cite{noakes} are derived explicitly. This procedure facilitates application of some of the mathematical theorems given in \cite{ringstrom}. As a consequence of these theorems, the existence of both $C^\infty$ solutions and maximal globally hyperbolic developments is proved. The obtained equations may be relevant for the stability analysis of the solutions under small perturbations of the initial data.

hep-th↗

arXiv2016

About the isocurvature tension between axion and high scale inflationary models

The present work suggests that the isocurvature tension between axion and high energy inflationary scenarios may be avoided by considering a double field inflationary model involving the hidden Peccei-Quinn Higgs and the Standard Model one. Some terms in the lagrangian we propose explicitly violate the Peccei-Quinn symmetry but, at the present era, their effect is completely negligible. The resulting mechanism allows a large value for the axion constant, of the order $f_a\sim M_p$, thus the axion isocurvature fluctuations are suppressed even when the scale of inflation $H_{inf}$ is very high, of the order of $H_{inf}\sim M_{gut}$. This numerical value is typical in Higgs inflationary models. An analysis about topological defect formation in this scenario is also performed, and it is suggested that, under certain assumptions, their effect is not catastrophic from the cosmological point of view.

hep-ph↗

arXiv2015

Zak Phase in Discrete-Time Quantum Walks

We report on a simple scheme that may present a non-trivial geometric Zak phase ($Φ_{Zak}$) structure, which is based on a discrete-time quantum walk architecture. By detecting the Zak phase difference between two trajectories connecting adjacent Dirac points where the quasi-energy gap closes for opposite values of quasi-momentum ($k$), it is possible to identify geometric invariants. These geometric invariants correspond to $|Φ_{Zak}^{+(-)}-Φ_{Zak}^{-(+)}|=π$ and $|Φ_{Zak}^{+(-)}-Φ_{Zak}^{+(-)}|=0$, we argue that this effect can be directly measured.

quant-ph↗

arXiv2015

Aspects of electrostatics in BTZ geometries

In the present paper the electrostatic of charges in non rotating BTZ black hole and wormhole space times is studied. In particular, the self force of a point charge in the geometry is characterized analitically. The differences between the self force in both cases is a theoretical experiment for distinguishing both geometries, which otherwise are locally indistinguishable. This idea was applied before to four and higher dimensional black holes by the present and other authors. However, the particularities of the BTZ geometry makes the analysis considerable more complicated than usual electrostatic in a flat geometry, and its even harder than its four dimensional counterparts. First, the BTZ space times are not asymptotically flat but instead asymptotically AdS. In addition, the relative distance $d(r,r+1)$ between two particles located at a radius $r$ and $r+1$ in the geometry tends to zero when $r\to\infty$. This behavior, which is radically different in a flat geometry, changes the analysis of the asymptotic conditions for the electrostatic field. In addition, there are no summation formulas that allow a closed analytic expression for the self force. We find a method to calculate such force in series, and the resulting expansion is convergent to the real solution. However, we suspect that the convergence is not uniform. In other, for points that are far away from the black hole the calculation of the force requires higher order summation. These subtleties are carefully analyzed in the paper, and it is shown that they lead to severe problems when calculating the self force for asymptotic points in the geometry.

hep-th↗