The Experts below are selected from a list of 25332 Experts worldwide ranked by ideXlab platform
Jiro Soda - One of the best experts on this subject based on the ideXlab platform.
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pulsar timing residual induced by ultralight vector dark matter
European Physical Journal C, 2020Co-Authors: Kimihiro Nomura, Asuka Ito, Jiro SodaAbstract:We study the ultralight vector dark matter with a mass around . The vector field oscillating coherently on galactic scales induces oscillations of the Spacetime Metric with a frequency around nHz, which is detectable by pulsar timing arrays. We find that the pulsar timing signal due to the vector dark matter has nontrivial angular dependence unlike the scalar dark matter and the maximal amplitude is three times larger than that of the scalar dark matter.
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pulsar timing residual induced by ultralight vector dark matter
arXiv: General Relativity and Quantum Cosmology, 2019Co-Authors: Kimihiro Nomura, Asuka Ito, Jiro SodaAbstract:We study the ultralight vector dark matter with a mass around $10^{-23}\,\mathrm{eV}$. The vector field oscillating coherently on galactic scales induces oscillations of the Spacetime Metric with a frequency around nHz, which is detectable by pulsar timing arrays. We find that the pulsar timing signal due to the vector dark matter has nontrivial angular dependence unlike the scalar dark matter and the maximal amplitude is three times larger than that of the scalar dark matter.
Kimihiro Nomura - One of the best experts on this subject based on the ideXlab platform.
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pulsar timing residual induced by ultralight vector dark matter
European Physical Journal C, 2020Co-Authors: Kimihiro Nomura, Asuka Ito, Jiro SodaAbstract:We study the ultralight vector dark matter with a mass around . The vector field oscillating coherently on galactic scales induces oscillations of the Spacetime Metric with a frequency around nHz, which is detectable by pulsar timing arrays. We find that the pulsar timing signal due to the vector dark matter has nontrivial angular dependence unlike the scalar dark matter and the maximal amplitude is three times larger than that of the scalar dark matter.
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pulsar timing residual induced by ultralight vector dark matter
arXiv: General Relativity and Quantum Cosmology, 2019Co-Authors: Kimihiro Nomura, Asuka Ito, Jiro SodaAbstract:We study the ultralight vector dark matter with a mass around $10^{-23}\,\mathrm{eV}$. The vector field oscillating coherently on galactic scales induces oscillations of the Spacetime Metric with a frequency around nHz, which is detectable by pulsar timing arrays. We find that the pulsar timing signal due to the vector dark matter has nontrivial angular dependence unlike the scalar dark matter and the maximal amplitude is three times larger than that of the scalar dark matter.
Yuri N. Obukhov - One of the best experts on this subject based on the ideXlab platform.
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Spacetime Metric from local and linear electrodynamics a new axiomatic scheme
Lecture Notes in Physics, 2006Co-Authors: Yuri N. Obukhov, Friedrich W. HehlAbstract:We consider Spacetime to be a 4-dimensional differentiable manifold that can be split locally into time and space. No Metric, no linear connection are assumed. Matter is described by classical fields/fluids. We distinguish electrically charged from neutral matter. Electric charge and magnetic flux are postulated'to be conserved. As a consequence, the inhornogeneous and the homogeneous Maxwell equations emerge expressed in terms of the excitation H == (H, D) and the field strength F = (E, B), respectively. H and F are assumed to fulfill a local and linear "Spacetime relation" with 36 constitutive functions. The propagation of electromagnetic waves is considered under such circumstances in the geoMetric optics limit. We forbid birefringence in vacuum-and find the light cone including its Lorentzian signature. Thus the conformally invariant part of the Metric is recovered. If one sets a scale, one finds the pseudo-Riemannian Metric of Spacetime.
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Spacetime Metric from local and linear electrodynamics a new axiomatic scheme
arXiv: General Relativity and Quantum Cosmology, 2005Co-Authors: Yuri N. Obukhov, Friedrich W. HehlAbstract:We consider Spacetime to be a 4-dimensional differentiable manifold that can be split locally into time and space. No Metric, no linear connection are assumed. Matter is described by classical fields/fluids. We distinguish electrically charged from neutral matter. Electric charge and magnetic flux are postulated to be conserved. As a consequence, the inhomogeneous and the homogeneous Maxwell equations emerge expressed in terms of the excitation H and the field strength F, respectively. H and F are assumed to fulfill a local and linear "Spacetime relation" with 36 constitutive functions. The propagation of electromagnetic waves is considered under such circumstances in the geoMetric optics limit. We forbid birefringence in vacuum and find the light cone including its Lorentzian signature. Thus the conformally invariant part of the Metric is recovered. If one sets a scale, one finds the pseudo-Riemannian Metric of Spacetime.
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on gravitational interaction of fermions
arXiv: General Relativity and Quantum Cosmology, 2001Co-Authors: Yuri N. ObukhovAbstract:We discuss some aspects of the gravitational interaction of the relativistic quantum particles with spin 1/2. The exact Foldy-Wouthuysen transformation is constructed for the Dirac particle coupled to the static Spacetime Metric. The quasi-relativistic limit of the theory is then analyzed. Using the analogous method, we obtain the exact Cini-Touschek transformation and discuss the ultra-relativistic limit of the fermion theory. We show that the Foldy-Wouthuysen transformation is not uniquely defined, and the corresponding ambiguity is deeply rooted in the relativistic quantum theory.
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Generally covariant Fresnel equation and the emergence of the light cone structure in linear pre-Metric electrodynamics
arXiv: General Relativity and Quantum Cosmology, 2001Co-Authors: Guillermo F. Rubilar, Yuri N. Obukhov, Friedrich W. HehlAbstract:We study the {\em propagation of electromagnetic waves} in a Spacetime devoid of a Metric but equipped with a {\em linear} electromagnetic Spacetime relation $H\sim\chi\cdot F$. Here $H$ is the electromagnetic excitation $({\cal D},{\cal H})$ and $F$ the field strength $(E,B)$, whereas $\chi$ (36 independent components) characterizes the electromagnetic permittivity/permeability of Spacetime. We derive analytically the corresponding Fresnel equation and show that it is always quartic in the wave covectors. We study the `Fresnel tensor density' ${\cal G}^{ijkl}$ as (cubic) function of $\chi$ and identify the leading part of $\chi$ (20 components) as indispensable for light propagation. Upon requiring electric/magnetic reciprocity of the Spacetime relation, the leading part of $\chi$ induces the {\em light cone} structure of Spacetime (9 components), i.e., the Spacetime Metric up to a function. The possible existence of an Abelian {\em axion} field (1 component of $\chi$) and/or of a {\em skewon} field (15 components) and their effect on light propagation is discussed in some detail. The newly introduced skewon field is expected to be T-odd and related to dissipation.
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Spacetime Metric from linear electrodynamics
Physics Letters B, 1999Co-Authors: Yuri N. Obukhov, Friedrich W. HehlAbstract:The Maxwell equations are formulated on an arbitrary (1 + 3)-dimensional manifold. Then, imposing a (constrained) linear constitutive relation between electromagnetic field (E, B) and excitation (D, H), we derive the Metric of Spacetime therefrom. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Sanatan Digal - One of the best experts on this subject based on the ideXlab platform.
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effects of oscillating Spacetime Metric background on a complex scalar field and formation of topological vortices
Physical Review D, 2021Co-Authors: Shreyansh S Dave, Sanatan DigalAbstract:We study the time evolution of a complex scalar field in the symmetry broken phase in the presence of oscillating Spacetime Metric background. In our ($2+1$)-dimensional simulations, we show that the Spacetime oscillations can excite an initial field configuration, which ultimately leads to the formation of topological vortices in the system. At late times, field configuration achieves a disordered state. A detailed study of the momentum and frequency modes of the field reveals that these field excitations are driven by the phenomenon of paraMetric resonance. In the extremely-high-frequency regime where frequency of Spacetime oscillations is much larger than the field-mass, the formed vortices are not topological in nature. Interestingly, in this regime, for a suitable choice of parameters of the simulation, we observe a persistent lattice structure of vortex-antivortex pairs. We discuss applications of our study to the dynamics of interior superfluidity of neutron stars during binary neutron star mergers, in generation of excitation in ultralight axionlike field near a strong gravitational wave source, etc.
Daniel Siemssen - One of the best experts on this subject based on the ideXlab platform.
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global existence of solutions of the semiclassical einstein equation for cosmological Spacetimes
Communications in Mathematical Physics, 2015Co-Authors: Nicola Pinamonti, Daniel SiemssenAbstract:We study the solutions of the semiclassical Einstein equation in flat cosmological Spacetimes driven by a massive conformally coupled scalar field. In particular, we show that it is possible to give initial conditions at finite time to get a state for the quantum field which gives finite expectation values for the stress–energy tensor. Furthermore, it is possible to control this expectation value by means of a global estimate on regular cosmological Spacetimes. The obtained estimates permit writing a theorem about the existence and uniqueness of the local solutions encompassing both the Spacetime Metric and the matter field simultaneously. Finally, we show that one can always extend local solutions up to a point where the scale factor a becomes singular or the Hubble function H reaches a critical value Hc = 180π/G, both of which correspond to a divergence of the scalar curvature R, namely a Spacetime singularity.
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global existence of solutions of the semiclassical einstein equation for cosmological Spacetimes
arXiv: Mathematical Physics, 2013Co-Authors: Nicola Pinamonti, Daniel SiemssenAbstract:We study the solutions of the semiclassical Einstein equation in flat cosmological Spacetimes driven by a massive conformally coupled scalar field. In particular, we show that it is possible to give initial conditions at finite time to get a state for the quantum field which gives finite expectation values for the stress-energy tensor. Furthermore, it is possible to control this expectation value by means of a global estimate on regular cosmological Spacetimes. The obtained estimates permit to write a theorem about the existence and uniqueness of the local solutions encompassing both the Spacetime Metric and the matter field simultaneously. Finally, we show that one can always extend local solutions up to a point where the scale factor becomes singular or the Hubble function reaches a critical value $H_c = 180\pi/G$, which both correspond to a divergence of the scalar curvature, namely a Spacetime singularity.