General Relativity And Quantum Cosmology
Bubble Networks: Framed Discrete Geometry for Quantum Gravity (1810.09364v2)
Laurent Freidel, Etera R. Livine
2018-10-22
In the context of canonical quantum gravity in 3+1 dimensions, we introduce a new notion of bubble network that represents discrete 3d space geometries. These are natural extensions of twisted geometries, which represent the geometrical data underlying loop quantum geometry and are defined as networks of SU(2) holonomies. In addition to the SU(2) representations encoding the geometrical flux, the bubble network links carry a compatible SL(2,R) representation encoding the discretized frame field which composes the flux. In contrast with twisted geometries, this extra data allows to reconstruct the frame compatible with the flux unambiguously. At the classical level this data represents a network of 3d geometrical cells glued together. The SL(2,R) data contains information about the discretized 2d metrics of the interfaces between 3d cells and SL(2,R) local transformations are understood as the group of area-preserving diffeomorphisms. We further show that the natural gluing condition with respect to this extended group structure ensures that the intrinsic 2d geometry of a boundary surface is the same from the viewpoint of the two cells sharing it. At the quantum level this gluing corresponds to a maximal entanglement along the network edges. We emphasize that the nature of this extension of twisted geometries is compatible with the general analysis of gauge theories that predicts edge mode degrees of freedom at the interface of subsystems.
Constructing the independent basis of total derivative curvature-dependent terms in 
(1812.01140v3)
Fabricio M. Ferreira, Ilya L. Shapiro
2018-12-04
Total derivative terms play an important role in the integration of conformal anomaly. In four dimensional space
there is only one such term, namely
. In the case of six dimensions
Deriving Hawking Radiation via Gauss-Bonnet Theorem: An Alternative Way (1902.04465v2)
A. Övgün, İ. Sakallı
2019-02-12
In this paper, we apply the recently found topological method of Robson, Villari and Biancalana (RVB) [1, 2] to the various black holes to derive their Hawking temperature. We show that the RVB method can easily be employed to compute the Hawking temperature of black holes having spherically symmetric topology. Therefore, we conclude that the RVB method provides a consistent formula to achieve the Hawking temperature using the topology.
A quasi-matter bounce equivalent to Starobinsky inflation (1902.05031v1)
L. F. Guimarães, F. T. Falciano, G. Brando
2019-02-13
In this paper we construct a bounce model that mimics the Starobinsky inflationary model. Our construction relies on Wands' duality, which shows that the Mukhanov-Sasaki equation has a symmetry transformation by changing appropriately its time-dependent mass term. One of the advantages of this constructive method is that one can control every contribution to the primordial power spectrum and check how far we can emulate a given primordial model with a different scenario. In particular, we show that mapping the Starobinsky inflation into a quasi-matter bounce gives the correct relation between the scalar spectral index
and the tensor-to-scalar ratio
.
Operational causality in spacetime (1902.05002v1)
Michał Eckstein, Paweł Horodecki, Ryszard Horodecki, Tomasz Miller
2019-02-13
We consider the general evolution of binary statistics in a, possibly curved, spacetime with the help of the optimal transport theory. It covers a wide range of models including classical statistics, quantum wave-packets and general, possibly non-linear, post-quantum theories. We postulate that any such evolution must satisfy a rigorous constraint encoding the intuition that (infinitesimal) probability parcels ought to travel along classical future-directed causal curves. We show that, surprisingly, its violation always has operational consequences leading to some form of superluminal signalling. In consequence, it establishes concrete limits on the validity of various models, in particular, the ones based on the Schr"odinger equation. Finally, we explain how the presented formalism establishes an unheralded link between the general theory of no-signalling boxes and relativistic spacetime physics.
Hair-dressing Horndeski: an approach to hairy solutions in cubic Horndeski gravity (1902.04988v1)
Reginald Christian Bernardo, Ian Vega
2019-02-13
In obtaining exact solutions in gravitational theories containing arbitrary model functions, such as Horndeski gravity, one usually starts by prescribing the model functions of the theory and then goes on to solving their corresponding field equations. In this paper, we explore the extent to which the reverse procedure can be useful, whereby one starts with desired solutions and then determines the models that support them. Working within the phenomenologically interesting cubic and shift-symmetric sector of Horndeski gravity, we develop a method for obtaining exact static and spherically-symmetric solutions, one of which happens to be a new hairy black hole. We study this black hole and its properties. We also discuss the limitations of the method and its possible extension to other Horndeski sectors.
Further refining the de Sitter swampland conjecture (1811.08889v2)
David Andriot, Christoph Roupec
2018-11-21
We propose an alternative refined de Sitter conjecture. It is given by a natural condition on a combination of the first and second derivatives of the scalar potential. We derive our conjecture in the same weak coupling, semi-classical regime where the previous refined de Sitter conjecture was derived, using the same tools together with a few more assumptions that we discuss. We further test and constrain free parameters in our conjecture using data points of a classical type IIA supergravity setup. Interestingly, our conjecture easily accommodates slow-roll single field inflation with a concave potential, favored by observations. The standard quintessence potential is in tension with our new conjecture, and we thus propose a different type of quintessence model.
Effective field theory for gravitational radiation in scalar-tensor gravity (1902.04941v1)
Adrien Kuntz, Federico Piazza, Filippo Vernizzi
2019-02-13
A light scalar degree of freedom, as the one possibly responsible for the accelerated expansion of the Universe, could leave observable traces in the inspiral gravitational wave signal of binary systems. In order to study these effects, we extend the effective field theory formalism of Goldberger and Rothstein to minimal scalar-tensor theories of gravity. This class of models is still very broad, because the couplings of the scalar to matter are far less constrained than those a massless spin-2 field. In most of the paper we focus on conformal couplings. Using the effective field theory approach, we discuss the emergence of violations of the strong equivalence principle even in models that exhibit universality of free fall at the microscopic level. Our results on the conservative dynamics of the binary and its power emitted in gravitational and scalar radiation agree with those obtained with the standard post-Newtonian formalism. We also compare them to more recent work. Finally, we discuss the implications of considering a disformal coupling to matter.
Accelerating parameter inference with graphics processing units (1902.04934v1)
D. Wysocki, R. O'Shaughnessy, Y-L. L. Fang, Jacob Lange
2019-02-13
Gravitational wave Bayesian parameter inference involves repeated comparisons of GW data to generic candidate predictions. Even with algorithmically efficient methods like RIFT or reduced-order quadrature, the time needed to perform these calculations and overall computational cost can be significant compared to the minutes to hours needed to achieve the goals of low-latency multimessenger astronomy. By translating some elements of the RIFT algorithm to operate on graphics processing units (GPU), we demonstrate substantial performance improvements, enabling dramatically reduced overall cost and latency.
Light Bending in Models with a Generic Scalar Field (1901.09760v2)
Dongjin Chway
2019-01-28
We study the deflection and time delay of light by the Sun in general scalar extensions of the Standard Model which may violate the equivalence principle. Despite the presence of the interaction
or
between the scalar field and photon, we show that the bending and time delay of light are the same as in Einstein's general relativity. The bending angle is obtained using geometrical optics and compared with the angle obtained using another method based on scattering amplitude. It is pointed out that the method based on scattering amplitude can lead to wrong conclusions about potential energy and light polarization. Also, we obtain a constraint on the generic scalar particle from the parametrized post-Newtonian parameter
, noting that planet motions are affected by the scalar field as in scalar-tensor theories with some modifications to the scalar field's couplings to the Sun and planets.
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