Browsing by Author "Alfaro, Jorge "

Now showing 1 - 7 of 7
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    A nontrivial footprint of standard cosmology in the future observations of low-frequency gravitational waves
    (2020) Alfaro, Jorge ; Gamonal San Martín, Mauricio
    Recent research shows that the cosmological components of the Universe should influence on the propagation of Gravitational Waves (GWs) and even it has been proposed a new way to measure the cosmological constant using Pulsar Timing Arrays (PTAs). However, these results have considered very particular cases (e.g. a de Sitter Universe or a mixing with non-relativistic matter). In this work we propose an extension of these results, using the Hubble constant as the natural parameter that includes all the cosmological information and studying its effect on the propagation of GWs. Using linearized gravity we considered a mixture of perfect fluids permeating the spacetime and studied the propagation of GWs within the context of the Lambda CDM model. We found from numerical simulations that the timing residual of local pulsars should present a distinguishable peak depending on the local value of the Hubble constant. As a consequence, when assuming the standard Lambda CDM model, our result predicts that the region of maximum timing residual is determined by the redshift of the source. This framework represents an alternative test for the standard cosmological model, and it can be used to facilitate the measurements of gravitational waves by ongoing PTAs projects.
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    Axial anomaly in very special relativity
    (2021) Alfaro, Jorge
    In this paper we study the axial anomaly in very special relativity electrodynamics using Pauli-Villars and dimensional regularization of ultraviolet divergences and Mandelstam-Leibbrandt regularization of infrared divergences. We compute the anomaly in 2 and 4 dimensional space-time. We find that this procedure preserves the vector Ward identity(charge conservation) and reproduce the standard axial anomaly in 2 and 4 dimensions without corrections from VSR. Finally, we show how to obtain the anomaly in the path integral approach.
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    Graviton mass bounds in very special relativity from binary pulsar's gravitational waves
    (2023) Santoni, Alessandro; Alfaro, Jorge; Soto, Alex
    In this work we study the gravitational radiation produced by a Keplerian binary system within the context of very special linear gravity (VSLG), a novel theory of linearized gravity in the framework of very special relativity allowing for a gauge-invariant mass mg of the graviton. For this task, we exploit effective field theory's techniques, which require, among others, the calculation of the squared amplitude of the emission process and therefore the polarization sum for VSLG gravitons. Working in the radiation zone and using the standard energy-momentum tensor's expression for Keplerian binaries, we derive and study the properties of the VSLG energy-loss and period-decrease rates, also verifying they reduce to the correct General Relativity limit when sending m(g) -> 0. Finally, using astronomical data from the Hulse-Taylor binary and the double pulsar J0737-3039, we obtain an upper bound on the VSLG graviton mass of mg similar to 10(-21) eV that, while being comparable to bounds obtained in this same way for other massive gravity models, is still weaker than the kinematical bound similar to 10(-22) eV obtained from the combined observation of the astronomical events GW170817 and GRB170817A, which should still hold in VSLG.
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    Infrared Regularization of Very Special Relativity Models
    (2024) Alfaro, Jorge
    We extend the Sim(2) invariant infrared regularization of Very Special Relativity models, that we have proposed recently, to include gamma 5 Dirac matrix. Then, we solve the Very Special Relativity Schwinger model, find the chiral anomaly, and clarify its meaning in the new context. In addition, we show that the triangle anomaly in four space-time dimensions agrees with the same object in standard quantum electrodynamics. Finally, we apply the infrared regularization to compute the large N limit of the Very Special Relativity Gross-Neveu model.
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    On the propagation of gravitational waves in a Lambda CDM universe
    (IOP PUBLISHING LTD, 2019) Alfaro, Jorge; Espriu, Domenec; Gabbanelli, Luciano
    We study here how the presence of non-zero matter density and a cosmological constant could affect the observation of gravitational waves in pulsar timing arrays. Conventionally, the effect of matter and cosmological constant is included by considering the redshift in frequency due to the expansion. However, there is an additional interesting effect due to the change of coordinates from the ones describing the geometry of the region where waves are produced to the ones used to measure the pulsar timing residuals. This change of coordinates is unavoidable as the strong gravitational field in a black hole merger distorts clocks and rules. Harmonic waves produced in such a merger become anharmonic when detected by a cosmological observer. The effect is tiny but appears to be nevertheless observable for the type of gravitational waves to which pulsar timing arrays are sensitive and for the favoured values of the cosmological parameters.
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    Thermodynamics of graviton condensate
    (2021) Alfaro, Jorge; Mancilla, Robinson
    In this work, we present the thermodynamic study of amodel that considers the black hole as a condensate of gravitons. In this model, the spacetime is not asymptotically flat because of a topological defect that introduces an angle deficit in the spacetime like in Global Monopole solutions. We have obtained a correction to the Hawking temperature plus a negative pressure associated with the black hole of mass M. In this way, the graviton condensate, which is assumed to be at the critical point defined by the condition mu(ch) = 0, has well-defined thermodynamic quantities P, V, T-h, S, and U as any other Bose-Einstein condensate (BEC). In addition, we present a formal equivalence between the Letelier spacetime and the line element that describes the graviton condensate. We also discuss the Kiselev black hole, which can parametrize the most well-known spherically symmetric black holes. Finally, we present a new metric, which we will call the BEC-Kiselev solution, that allows us to extend the graviton condensate to the case of solutions with different matter contents.
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    Very special linear gravity: A gauge-invariant graviton mass
    (2022) Alfaro, Jorge; Santoni, Alessandro
    Linearized gravity in the Very Special Relativity (VSR) framework is considered. We prove that this theory allows for a non-zero graviton mass m(g) without breaking gauge invariance nor modifying the relativistic dispersion relation. We find the analytic solution for the new equations of motion in our gauge choice, verifying as expected the existence of only two physical degrees of freedom. Finally, through the geodesic deviation equation, we confront some results for classic gravitational waves (GW) with the VSR ones: we see that the ratios between VSR effects and classical ones are proportional to (m(g)/E)(2), E being the energy of a graviton in the GW. For GW detectable by the interferometers LIGO and VIRGO this ratio is at most 10(-20). However, for GW in the lower frequency range of future detectors, like LISA, the ratio increases significantly to 10(-)(10), that combined with the anisotropic nature of VSR phenomena may lead to observable effects. (C) 2022 The Authors. Published by Elsevier B.V.