Martin G. Richarte

Martin G. Richarte

Universidade Federal do Espírito Santo
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Martin G. Richarte has a total of 30 co-authors. Here are the top co-authors by number of shared publications:

Latest Publications

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    In-depth analysis of violations of the strong equivalence principle in scalarized Einstein-Gauss-Bonnet theories

    by Martín G. Richarte, Júnior D. Toniato

    Cited by 2
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    Quasar pairs as large-scale structure tracers

    by Martín G. Richarte, Facundo Toscano, Diego Garcia Lambas, Heliana E. Luparello, Luiz Filipe Guimarães, Júlio C. Fabris

    Aims. Quasars can be used as suitable tracers of the large-scale distribution of galaxies at high redshift given their high luminosity and dedicated surveys. Previous studies have shown that quasars have a bias similar to that of rich groups. Following this argument, quasar pairs could be associated with higher-density environments serving as protocluster proxies. Methods. In this work, our aim is to characterize close quasar pairs residing in the same halo. This is accomplished by identifying quasar pairs in redshift space. We analyze pair-quasar cross correlations, as well as cosmic microwave background (CMB)-derived lensing convergence profiles centered on quasar and quasar pairs. Results. We identified quasar pairs in the SDSS-DR16 catalog as objects with relative velocities within |ΔV|≤900 km/s and projected separation less than dp ≤ 2 Mpc, in the redshift range 1.2 ≤ z ≤ 2.8. We computed redshift-space cross-correlation functions using Landy-Szalay estimators for the samples. For the analysis of the correlation between quasars or quasar pairs and the underlying mass distribution, we calculated mean radial profiles of the lensing convergence parameter using CMB data provided by the Planck Collaboration. Conclusions. We identified 2777 pairs of quasars in the redshift range 1.2–2.8. Quasar pairs show a distribution of relative luminosities that differs from that found in two pairs selected at random with the same redshift distribution, indicating that quasars in these systems distinguish themselves from isolated ones. The cross-correlation between pairs and quasars shows a larger correlation amplitude than the autocorrelation function of quasars, indicating that these systems are more strongly biased with respect to the large-scale mass distribution and reside in more massive halos. This is reinforced by the higher convergence CMB lensing profiles of the pairs compared to isolated quasars with a similar redshift distribution. Our results show that quasar pairs are suitable precursors of present-day clusters of galaxies, in contrast to isolated quasars, which are associated with more moderate density environments.

    Cited by 6
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    Exploring dark sector interactions with delta effective theories

    by Martín G. Richarte, Luiz Filipe Guimarães, Susana J. Landau, Júlio C. Fabris

    Cited by 4
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    Exploring scalarized Einstein-Gauss-Bonnet theories through the lens of parametrized post-Newtonian formalism

    by Martín G. Richarte, Júnior D. Toniato

    Cited by 4
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    Exploring Scalarized Einstein-Gauss-Bonnet Theories Through the Lens of Parametrized Post-Newtonian Formalism

    by Martín G. Richarte, Júnior D. Toniato

    We explore scalarized Einstein-Gauss-Bonnet theories within the context of the Parameterized Post-Newtonian formalism, which serves as a robust framework for examining modifications to General Relativity that exhibit scalarization. This approach enables us to impose a variety of constraints on the parameter space, particularly focusing on the PPN parameters $γ$ and $β$. Our analysis reveals several significant bounds for each scalarized model, utilizing data from the Cassini mission, Lunar Laser Ranging, and the forthcoming BepiColombo mission, in conjunction with geodetic Very Long Baseline Interferometry measurements around the Sun. In particular, we conducted a combined analysis of the MESSENGER mission's precision measurements of Mercury's perihelion precession $\dotω$ alongside the Cassini constraints on $γ$, yielding intriguing limits for the Ricci-EGB model. Furthermore, we investigate the impact of the new post-Newtonian potential introduced by the Gauss-Bonnet term at fourth order, which necessitates an expanded formulation of the PPN parameters. This highlights that the parameter $β$ exhibits different effects when analyzing the Ricci-EGB model. Additional constraints are derived from this framework by estimating the $γ$ PPN parameter using data from strong-lensing galaxy systems.

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    Post-Newtonian analysis of regularized 4D Einstein-Gauss-Bonnet theory: Complete set of PPN parameters and observational constraints

    by Júnior D. Toniato, Martín G. Richarte

    We performed a post-Newtonian analysis of the regularized four-dimensional Einstein-Gauss-Bonnet gravitational theory. The resulting metric differs from the classical parametrized post-Newtonian (PPN) formalism in that a new gravitational potential arises from the integration of the approximate field equations. We also investigated the conserved quantities and equations of motion for massive bodies and light rays to a certain degree. By computing the predicted periastron advance rate in a binary system, we obtained an observational constraint that is stronger than those of previous analyses. Although the usual 10 PPN parameters can still be derived within the PPN framework, an extra parameter is needed to account for the full post-Newtonian tests.

    Cited by 8
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    Scattering and absorption of a scalar field impinging on a charged black hole in the Einstein-Maxwell-dilaton theory

    by Martín G. Richarte, Ébano L. Martins, Júlio C. Fabris

    This study revisits the absorption and scattering process by which a massless scalar field impinges on a charged-dilatonic black hole. First, we review the classical analysis to obtain the deflection angle and the differential scattering cross section in terms of the mass, electric charge and dilatonic charge. Then, using the partial wave method, we determine the total absorption cross section numerically in terms of the decoupling parameter called Mω, finding that the amplitude of the dilatonic black hole is lower than the Reissner-Nordström one for mild frequencies. In the high-frequency limit, the absorption cross section exhibits two different complex behaviors; the fine structure and the hyperfine structure. For the differential scattering cross section, smaller values of Mω lead to more significant amplitudes; the opposite scenario is obtained by increasing the charge-to-mass ratio. To fully grasp the main properties of the charged dilatonic black hole, we consider a different framework where the compact object is impinged by a charged massive scalar field. The superradiant effect is lessened for intermediate frequency concerning the Reissner-Nordström case. However, this effect does not necessarily imply the existence of any dynamical instability. In order to trigger the superradiant instability, unstable modes must remain trapped outside the event horizon with a mechanism based on the reflecting-mirror boundary conditions. In this way, a charged scalar field plus a charged black hole configure a charged black hole bomb. We provide an analytic formula (lower bound) for the values of the charge field, which can trigger this superradiant instability. We extend this minimal setup by considering the dilaton perturbations while freezing the other degree of freedom. The new perturbation scheme enhances the superradiance scattering and reduces the lower bound of the charge-to-mass ratio to develop a superradiant instability.

    Cited by 34
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    Scattering and absorption of a scalar field impinging on a charged black hole in the Einstein-Maxwell-dilaton theory

    by Martín G. Richarte, Ébano L. Martins, Júlio C. Fabris

    This study revisits the absorption and scattering process by which a massless scalar field impinges on a charged dilatonic black hole. First, we review the classical analysis to obtain the deflection angle and the differential scattering cross-section. Then, using the partial wave method, we determine the total absorption cross-section numerically in terms of the decoupling parameter called $M\omega$, finding that the amplitude of the dilatonic black hole is lower than the Reissner-Nordstr\"om one for mild frequencies. In the high-frequency limit, the absorption cross-section exhibits two different complex behaviors; the fine structure and the hyperfine structure. For the differential scattering cross-section, smaller values of $M\omega$ lead to more significant amplitudes; the opposite scenario is obtained by increasing the charge-to-mass ratio. To fully grasp the main properties of the charged dilatonic black hole, we consider a different framework where the compact object is impinged by a charged massive scalar field. The superradiant effect is lessened for intermediate frequency concerning the Reissner-Nordstr\"om case. However, this effect does not necessarily imply the existence of any dynamical instability. In order to trigger the superradiant instability, unstable modes must remain trapped outside the event horizon with a mechanism based on the reflecting-mirror boundary conditions. In this way, a charged scalar field plus a charged black hole configure a charged black hole bomb. We provide an analytic formula (lower bound) for the values of the charge field, which can trigger this superradiant instability. We extend this minimal setup by considering the dilaton perturbations while freezing the other degree of freedom. The new perturbation scheme enhances the superradiance scattering and reduces the lower bound of the charge-to-mass ratio to develop a superradiant instability.

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    Quasinormal modes and self-adjoint extensions of the Schrödinger operator

    by Júlio C. Fabris, Martín G. Richarte, Alberto Saa

    We revisit here the analytical continuation approach usually employed to compute quasinormal modes (QNM) and frequencies of a given potential barrier V starting from the bounded states and respective eigenvalues of the Schrödinger operator associated with the potential well corresponding to the inverted potential −V. We consider an exactly soluble problem corresponding to a potential barrier of the Poschl-Teller type with a well defined and behaved QNM spectrum, but for which the associated Schrödinger operator H obtained by analytical continuation fails to be self-adjoint. Although H admits self-adjoint extensions, we show that the eigenstates corresponding to the analytically continued QNM do not belong to any self-adjoint extension domain and, consequently, they cannot be interpreted as authentic quantum mechanical bounded states. Our result challenges the practical use of the this type of method when H fails to be self-adjoint since, in such cases, we would not have in advance any reasonable criterion to choose the initial eigenstates of H which would correspond to the analytically continued QNM.

    Cited by 16
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    Quasinormal modes and self-adjoint extensions of the Schroedinger operator

    by Júlio C. Fabris, Martín G. Richarte, Alberto Saa

    We revisit here the analytical continuation approach usually employed to compute quasinormal modes (QNM) and frequencies of a given potential barrier $V$ starting from the bounded states and respective eigenvalues of the Schroedinger operator associated with the potential well corresponding to the inverted potential $-V$. We consider an exactly soluble problem corresponding to a potential barrier of the Poschl-Teller type with a well defined and behaved QNM spectrum, but for which the associated Schroedinger operator $\cal H$ obtained by analytical continuation fails to be self-adjoint. Although $\cal H$ admits self-adjoint extensions, we show that the eigenstates corresponding to the analytically continued QNM do not belong to any self-adjoint extension domain and, consequently, they cannot be interpreted as authentic quantum mechanical bounded states. Our result challenges the practical use of the this type of method when $\cal H$ fails to be self-adjoint since, in such cases, we would not have in advance any reasonable criterion to choose the initial eigenstates of $\cal H$ which would correspond to the analytically continued QNM.

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