Papers by ulises nucamendi
arXiv (Cornell University), Jul 10, 2023
With focus on the cosmological evolution of linear perturbations of matter and geometry, we calcu... more With focus on the cosmological evolution of linear perturbations of matter and geometry, we calculate the equivalent expressions to that of the Newtonian and Synchronous gauges within the framework of Unimodular Gravity, being these two gauges commonly used and implemented in Boltzmann codes. An important aspect of our analysis is the inclusion of the energy-momentum current violation, as well as its perturbations. Moreover, for the first time we demonstrate that it is possible to fix both gauges consistently, although as it has been already noticed in previous literature, neither of them is recovered in the sense of the dynamics given in General Relativity for matter and metric fluctuations. Specifically, we show that since the unimodular constraint at the level of linear perturbations lead to only one degree of freedom of scalar modes of metric fluctuations, the dynamics in Unimodular Gravity forces to keep the anisotropic stress in the Newtonian gauge, whereas the cold dark matter comoving frame can not be set in the Synchronous gauge. The physical implications on the density contrast of cold dark matter is reviewed, and the Sachs-Wolfe effect is obtained and compared with previous results in the literature of cosmological perturbations in Unimodular Gravity.
Journal of Cosmology and Astroparticle Physics, Aug 1, 2022
Modified theories of gravity yield an effective dark energy in the background dynamics that achie... more Modified theories of gravity yield an effective dark energy in the background dynamics that achieves an accelerated expansion of the universe. In addition, they present a fifth force that induces gravitational signatures in structure formation, and therefore in the matter power spectrum and related statistics. On the other hand, massive neutrinos suppress the power spectrum at scales that also modified gravity enhances it, so a degeneration of these effects has been recognized for some gravity models. In the present work, we study both effects using kinetic gravity braiding (nKGB) models to find that in spite of some degeneracies, the role of the fifth force at very large scales imprints a bump in the matter power spectrum as a distinctive signature of this model and, therefore, acts as a smoking gun that seems difficult to match within the present knowledge of power spectra. These models result interesting, however, since the n = 1 presents no H 0 tension, and all nKGB studied here present no σ 8 tension and, in addition, a null neutrino mass is excluded.
arXiv (Cornell University), Feb 22, 2023
Astronomische Nachrichten, 2021
We derive closed formulas for the mass and spin parameters of a Kerr black hole in terms of a min... more We derive closed formulas for the mass and spin parameters of a Kerr black hole in terms of a minimal quantity of observational data: the red-/blue-shifts of photons emitted by massive particles (stars) moving on geodesics around the black hole and their respective orbital radius. It turns out that given a set of two (three) stars revolving around the black hole, these formulas involve just eight (twelve) observational data. For the case of a single star orbiting the black hole we need a minimal set of four observational measurements to analytically determine both parameters.
Journal of High Energy Physics, Nov 30, 2007
Photon-graviton mixing in an electromagnetic field is a process of potential interest for cosmolo... more Photon-graviton mixing in an electromagnetic field is a process of potential interest for cosmology and astrophysics. At the tree level it has been studied by many authors. We consider the one-loop contribution to this amplitude involving a charged spin 0 or spin 1/2 particle in the loop and an arbitrary constant field. In the first part of this article, the worldline formalism is used to obtain a compact two-parameter integral representation for this amplitude, valid for arbitrary photon energies and background field strengths. The calculation is manifestly covariant througout.
arXiv (Cornell University), Jun 28, 2022
In this paper we perform a thorough dynamical systems analysis of the cubic galileon model nonmin... more In this paper we perform a thorough dynamical systems analysis of the cubic galileon model nonminimally coupled to the dark matter. Three well-known classes of interacting models are considered where the energy exchange between the dark components is a function of the dark matter density and of the dark energy density: Q1 = 3αHρm, Q2 = 3βρmφ and Q3 = 3ǫHρ φ , respectively. We are able to show the global asymptotic dynamics of the model for the exponential potential in a homogeneous and isotropic background. The cosmological implications of the proposed scenarios are explored and it is found that, in addition to the appearance of new equilibrium configurations that do not appear neither in the non-interacting cubic galileon model nor in the interacting quintessence model, there is a significant impact of the non-minimal coupling through modification of the stability properties of the critical points. The resulting cosmological scenario provides a bigbang origin of the cosmic expansion, an early transient stage of inflationary expansion, as well as matter-scaling late time stable state of the universe, among other solutions of lesser cosmological interest. This work extends previous studies of coupled dark energy to a broader class of gravitational theories.
SSRN Electronic Journal
In this paper we perform a thorough dynamical systems analysis of the cubic galileon model nonmin... more In this paper we perform a thorough dynamical systems analysis of the cubic galileon model nonminimally coupled to the dark matter. Three well-known classes of interacting models are considered where the energy exchange between the dark components is a function of the dark matter density and of the dark energy density: Q1 = 3αHρm, Q2 = 3βρmφ and Q3 = 3ǫHρ φ , respectively. We are able to show the global asymptotic dynamics of the model for the exponential potential in a homogeneous and isotropic background. The cosmological implications of the proposed scenarios are explored and it is found that, in addition to the appearance of new equilibrium configurations that do not appear neither in the non-interacting cubic galileon model nor in the interacting quintessence model, there is a significant impact of the non-minimal coupling through modification of the stability properties of the critical points. The resulting cosmological scenario provides a bigbang origin of the cosmic expansion, an early transient stage of inflationary expansion, as well as matter-scaling late time stable state of the universe, among other solutions of lesser cosmological interest. This work extends previous studies of coupled dark energy to a broader class of gravitational theories.
Journal of Physics A, Apr 9, 2008
Einstein-Maxwell theory implies the mixing of photons with gravitons in an external electromagnet... more Einstein-Maxwell theory implies the mixing of photons with gravitons in an external electromagnetic field. This process and its possible observable consequences have been studied at tree level for many years. We use the worldline formalism for obtaining an exact integral representation for the one-loop corrections to this amplitude due to scalars and fermions. We study the structure of this amplitude, and obtain exact expressions for various limiting cases.
Astronomy & Astrophysics
In this work we make use of a general relativistic method to estimate the mass-to-distance ratio ... more In this work we make use of a general relativistic method to estimate the mass-to-distance ratio M/D = 3.54−0.18+0.20 × 104 M⊙ Mpc−1 of the black hole hosted at the core of the active galactic nucleus of TXS 2226–184, along with its right ascension offset and the recession redshift (velocity) of the galaxy. Our statistical fit is based on the frequency shift of photons emitted by water masers and their orbital positions when circularly revolving around the black hole center within the accretion disk of the active galactic nucleus. By taking a previously reported distance to the galaxy into account, we compare the result of the black hole mass fit to an estimate based on a mass-luminosity correlation. We find that the black hole mass at the core of TXS 2226–184 obtained with the aid of the statistical fit using the general relativistic method, M = 3.67−0.18+0.20 × 106 M⊙, is approximately 0.6 times the black hole mass, MBH = 6.24−2.27+3.63 × 106 M⊙, which was computed with the mass–l...
Physical Review D
We extract the Hubble law by the frequency-shift considerations of test particles revolving the K... more We extract the Hubble law by the frequency-shift considerations of test particles revolving the Kerr black hole in asymptotically de Sitter spacetime. To this end, we take into account massive geodesic particles circularly orbiting the Kerr-de Sitter black holes that emit redshifted photons towards a distant observer which is moving away from the emitter-black hole system. By considering this configuration, we obtain an expression for redshift in terms of the spacetime parameters, such as mass, angular momentum, and the cosmological constant. Then, we find the frequency shift of photons versus the Hubble constant with the help of some physically motivated approximations. Finally, some exact formulas for the Schwarzschild black hole mass and the Hubble constant in terms of the observational redshift of massive bodies circularly orbiting this black hole are extracted. Our results suggest a new independent general relativistic approach to obtaining the late-time Hubble constant in terms of observable quantities.
Monthly Notices of the Royal Astronomical Society
In this work, we perform a Bayesian statistical fit to estimate the mass-to-distance ratio and th... more In this work, we perform a Bayesian statistical fit to estimate the mass-to-distance ratio and the recessional redshift of 10 different black holes hosted at the centre of active galactic nuclei, namely the galaxies NGC 5765b, NGC 6323, UGC 3789, CGCG 074−064, ESO 558−G009, NGC 2960, NGC 6264, NGC 4388, J0437+2456, and NGC 2273. Our general relativistic method makes use of the positions in the sky and frequency shift observations of water megamasers circularly orbiting the central black hole on their accretion discs. This approach also allows us to quantify the gravitational redshift that is not considered in a Newtonian analysis. The gravitational redshift of the megamasers closest to the black hole is found to be within the range 1–6 km s−1. The order of the fitted black hole masses corresponds to supermassive black holes and lies on the range 106−107M⊙.
In this paper, we investigate the Penrose process in the purlieus of the axially symmetric magnet... more In this paper, we investigate the Penrose process in the purlieus of the axially symmetric magnetised Reissner-Nordström black hole for both neutral and charged particles. We start with the study of the geometry of the black hole and find the regions where the $g_{tt}$ component of the metric tensor is positive (i.e. $g_{tt}>0$). It is interestingly found that the condition $g_{tt}>0$ is fulfilled not only close to the event horizon known as the ergosphere but also far away from the event horizon in the silhouette of potential wells. We also show that as the dimensionless magnetic field $B$ increases the silhouette of potential wells for which $g_{tt}>0$ grows correspondingly and eventually merges with ergoregion when $B\gtrsim 1.6$. Finally, we investigate the efficiency of the Penrose process for the axially symmetric magnetized black hole case and bring out the effect of the magnetic field on it. Further, we also compare our results with the one for Kerr black hole. We show that when the charge $Q$ of the black hole is kept constant, the efficiency of the energy extraction process for the case of {a neutral particle (i.e. $q/m=0$) first increases and then begins to decrease with rise in the value of $B$ field, in contrast to Kerr black hole where it always increases as the rotation parameter grows. However, for the case of a charged particle (i.e. $q\neq 0$) the efficiency always increases with the rise in the $B$ field and can go over $100\%$, when both $B$ and $q/m$ are large enough (say $B\approx1$ and $q/m>2.2$)}. It is worth noting that the existence of regions away from the horizon where $g_{tt}>0$ also favours the energy-extraction process away from the effect of the black hole. However, the energy extraction from these regions is pure consequence of the magnetic field.
In this work, we elaborate on the development of a general relativistic formalism that allows one... more In this work, we elaborate on the development of a general relativistic formalism that allows one to analytically express the mass and spin parameters of the Kerr black hole in terms of observational data: the total redshift and blueshift of photons emitted by geodesic massive particles revolving the black hole and their orbital parameters. Thus, we present concise closed formulas for the mass and spin parameters of the Kerr black hole in terms of few directly observed quantities in the case of equatorial circular orbits either when the black hole is static or is moving with respect to a distant observer. Furthermore, we incorporate the gravitational dragging effect generated by the rotating nature of the Kerr black hole into the analysis and elucidate its non-trivial contribution to the expression for the light bending parameter and the frequency shifts of photons emitted by orbiting particles that renders simple symmetric expressions for the kinematic redshift and blueshift. We also incorporate the dependency of the frequency shift on the azimuthal angle, a fact that allows one to express the total redshift/blueshift along any point of the orbit of the revolving particle for the cases when the black hole is both static or moving with respect to us. These formulas allow one to compute the Kerr black hole parameters by applying this general relativistic formalism to astrophysical systems like the megamaser accretion disks orbiting supermassive black holes at the core of active galactic nuclei. Our results open a new window to implement parameter estimation studies to constrain black hole variables, and they can be generalized to black hole solutions beyond Einstein gravity.
Marcelo Salgado, Daniel Sudarsky Instituto de Ciencias Nucleares Universidad Nacional Autónoma de... more Marcelo Salgado, Daniel Sudarsky Instituto de Ciencias Nucleares Universidad Nacional Autónoma de México Apdo. Postal 70-543 México 04510 D.F, México and Ulises Nucamendi Departamento de F́ısica Centro de Investigación y de Estudios Avanzados del I.P.N. A. P. 14-741, México, D. F. 07000, México. Abstract We study in the physical frame the phenomenon of spontaneous scalarization that occurs in scalar-tensor theories of gravity for compact objects. We discuss the fact that the phenomenon occurs exactly in the regime where the Newtonian analysis indicates it should not. Finally we discuss the way the phenomenon depends on the equation of state used to describe the nuclear matter.
In this paper we compute the Arnowitt-Deser-Misner (ADM) mass, the angular momentum and the charg... more In this paper we compute the Arnowitt-Deser-Misner (ADM) mass, the angular momentum and the charge of the Kerr black hole solution in the scalar-tensor-vector gravity theory [known as the Kerr-MOG (modified-gravity) black hole configuration]; we study in detail as well several properties of this solution such as the stationary limit surface, the event horizon, and the ergosphere, and conclude that the new deformation parameter α affects the geometry of the Kerr-MOG black hole significantly in addition to the ADM mass and spin parameters. Moreover, the ADM mass and black hole event horizon definitions allow us to set a novel upper bound on the deformation parameter and to reveal the correct upper bound on the black hole spin. We further find the geodesics of motion of stars and photons around the Kerr-MOG black hole. By using them we reveal the expressions for the mass and the rotation parameter of the Kerr-MOG black hole in terms of the red-and blueshifts of photons emitted by geodesic particles, i.e., by stars. These calculations supply a new and simple method to further test the general theory of relativity in its strong field limit: If the measured redand blueshifts of photons exceed the bounds imposed by the general theory of relativity, then the black hole is not of Kerr type. It could also happen that the measurements are allowed by the Kerr-MOG metric, implying that the correct description of the dynamics of stars around a given black hole should be performed using MOG or another modified theory of gravity that correctly predicts the observations. In particular, this method can be applied to test the nature of the putative black hole hosted at the center of the Milky Way in the near future.
Recently, in [1] we developed a parametric reconstruction method to a homogeneous, isotropic and ... more Recently, in [1] we developed a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of dark energy (DE) with constant equation of state (EOS) parameter interacting with dark matter (DM). The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which form a complete set orthonormal functions. In this article, we reconstruct the interaction function expanding it in terms of only the first four Chebyshev polynomials and obtain the best estimation for the coefficients of the expansion assuming three models: (a) a DE equation of the state parameter w=-1 (an interacting cosmological Lambda), (b) a DE equation of the state parameter w = constant with a dark matter density parameter fixed, (c) a DE equation of the state parameter w = constant with a free constant dark matter density parameter to be...
In this paper we investigate the asymptotic dynamics of inflationary cosmological models that are... more In this paper we investigate the asymptotic dynamics of inflationary cosmological models that are based in scalar-tensor theories of gravity. Our main aim is to explore the global structure of the phase space in the framework of single-field inflation models. For this purpose we make emphasis in the adequate choice of the variables of the phase space. Our results indicate that, although single-field inflation is generic in the sense that the corresponding critical point in the phase space exists for a wide class of potentials, along given phase space orbits – representing potential cosmic histories – the occurrence of the inflationary stage is rather dependent on the initial conditions. For the non-minimal coupling model with the ϕ^2-potential, we have been able to give a rough estimate of the relative probability for initial conditions leading to slow-roll inflation: 10^-13 %≲ RP≪ 10^-8 %. These bonds are greatly improved in the scalar-tensor models, including the Brans-Dicke theor...
In U. Nucamendi et al. Phys. Rev. D63 (2001) 125016 and K. Lake, Phys. Rev. Lett. 92 (2004) 05110... more In U. Nucamendi et al. Phys. Rev. D63 (2001) 125016 and K. Lake, Phys. Rev. Lett. 92 (2004) 051101 it has been shown that galactic potentials can be kinematically linked to the observed red/blue shifts of the corresponding galactic rotation curves under a minimal set of assumptions: the emitted photons come from stable timelike circular geodesic orbits of stars in a static spherically symmetric gravitational field, and propagate to us along null geodesics. It is remarkable that this relation can be established without appealing at all to a concrete theory of gravitational interaction. Here we generalize this kinematical spherically symmetric approach to the galactic rotation curves problem to the stationary axisymmetric realm since this is precisely the symmetry that spiral galaxies possess. Thus, by making use of the most general stationary axisymmetric metric, we also consider stable circular orbits of stars that emit signals which travel to a distant observer along null geodesics...
The Isolated Horizons (IH) formalism, together with a simple phenomenological model for colored b... more The Isolated Horizons (IH) formalism, together with a simple phenomenological model for colored black holes has been used to predict non-trivial formulae that relate the ADM mass of the solitons and hairy Black Holes of Gravity-Matter system on the one hand, and several horizon properties of the black holes in the other. In this article, the IH formalism is tested numerically for spherically symmetric solutions to an Einstein-Higgs system where hairy black holes were recently found to exist. It is shown that the mass formulae still hold and that, by appropriately extending the current model, one can account for the behavior of the horizon properties of these new solutions. An empirical formula that approximates the ADM mass of hairy solutions is put forward, and some of its properties are analyzed.
By means of a combined use of the type Ia supernovae and H(z) data tests, together with the study... more By means of a combined use of the type Ia supernovae and H(z) data tests, together with the study of the asymptotic properties in the equivalent phase space - through the use of the dynamical systems tools - we demonstrate that the bulk viscous matter-dominated scenario is not a good model to explain the accepted cosmological paradigm, at least, under the parametrization of bulk viscosity considered in this paper. The main objection against such scenarios is the absence of conventional radiation and matter-dominated critical points in the phase space of the model. This entails that radiation and matter dominance are not generic solutions of the cosmological equations, so that these stages can be implemented only by means of unique and very specific initial conditions, i. e., of very unstable particular solutions. Such a behavior is in marked contradiction with the accepted cosmological paradigm which requires of an earlier stage dominated by relativistic species, followed by a perio...
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Papers by ulises nucamendi