Fri - 07/01/22

Constraining the Barbero-Immirzi parameter from the duration of inflation in Loop Quantum Cosmology

  • Authors: L. N. Barboza, G. L. L. W. Levy, L. L. Graef, Rudnei O. Ramos
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2206.14881
  • Abstract We revisit the predictions for the duration of the inflationary phase after the bounce in Loop Quantum Cosmology. We present our analysis for different classes of inflationary potentials that include the monomial power-law chaotic type of potentials, the Starobinsky and the Higgs-like symmetry breaking potential with different values for the vacuum expectation value. Our set up can easily be extended to other forms of primordial potentials than the ones we have considered. Independently on the details of the contracting phase, if the dynamics starts sufficiently in the far past, the kinetic energy will come to dominate at the bounce, uniquely determining the amplitude of the inflaton at this moment. This will be the initial condition for the further evolution that will provide us with results for the number of {\it e}-folds from the bounce to the beginning of the accelerated inflationary regime and the subsequent duration of inflation. We also discuss under which conditions each model considered could lead to observable signatures on the spectrum of the Cosmic Microwave Background (CMB), or, else, be excluded for not predicting a sufficient amount of accelerated expansion. A first analysis is performed considering the standard value for the Barbero-Immirzi parameter, $\gamma \simeq 0.2375$, which is obtained from black hole entropy calculations. In a second analysis, we consider the possibility of varying the value of this parameter, which is motivated by the fact that the Barbero-Immirzi parameter can be considered a free parameter of the underlying quantum theory in the context of Loop Quantum Gravity. {}From this analysis, we obtain a lower limit for this parameter by requiring the minimum amount of inflationary expansion that makes the model consistent with the CMB observations.

The Complete Barrett-Crane Model and its Causal Structure

  • Authors: Alexander F. Jercher, Daniele Oriti, Andreas G. A. Pithis
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2206.15442
  • Abstract The causal structure is a quintessential element of continuum spacetime physics and needs to be properly encoded in a theory of Lorentzian quantum gravity. Established spin foam (and tensorial group field theory (TGFT)) models mostly work with relatively special classes of Lorentzian triangulations (e.g. built from spacelike tetrahedra only), obscuring the explicit implementation of the local causal structure at the microscopic level. We overcome this limitation and construct a full-fledged model for Lorentzian quantum geometry the building blocks of which include spacelike, lightlike and timelike tetrahedra. We realize this within the context of the Barrett-Crane TGFT model. Following an explicit characterization of the amplitudes via methods of integral geometry, and the ensuing clear identification of local causal structure, we analyze the model’s amplitudes with respect to its (space)time-orientation properties and provide also a more detailed comparison with the framework of causal dynamical triangulations (CDT).

The Complete Barrett-Crane Model and its Causal Structure

  • Authors: Alexander F. Jercher, Daniele Oriti, Andreas G. A. Pithis
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2206.15442
  • Abstract The causal structure is a quintessential element of continuum spacetime physics and needs to be properly encoded in a theory of Lorentzian quantum gravity. Established spin foam (and tensorial group field theory (TGFT)) models mostly work with relatively special classes of Lorentzian triangulations (e.g. built from spacelike tetrahedra only), obscuring the explicit implementation of the local causal structure at the microscopic level. We overcome this limitation and construct a full-fledged model for Lorentzian quantum geometry the building blocks of which include spacelike, lightlike and timelike tetrahedra. We realize this within the context of the Barrett-Crane TGFT model. Following an explicit characterization of the amplitudes via methods of integral geometry, and the ensuing clear identification of local causal structure, we analyze the model’s amplitudes with respect to its (space)time-orientation properties and provide also a more detailed comparison with the framework of causal dynamical triangulations (CDT).

  1. [2206.15422] - Space and time transformations with a minimal length - Pasquale Bosso

  2. [2206.14814] - A universal formula for the density of states with continuous symmetry - Monica Jinwoo Kang, Jaeha Lee, Hirosi Ooguri

  3. [2206.15262] - Open String Probe in Soft Hair BTZ - Chi-Hsien Tai, Sayid Mondal, Wen-Yu Wen

  4. [2206.15357] - Supersymmetric Spectral Form Factor and Euclidean Black Holes - Sunjin Choi, Seok Kim, Jaewon Song

Thu - 06/30/22

There is no new related paper today

Radiative corrections to the Lorentzian EPRL spin foam propagator

  • Authors: Pietro Donà, Pietropaolo Frisoni, Edward Wilson-Ewing
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2206.14755
  • Abstract We numerically estimate the divergence of several two-vertex diagrams that contribute to the radiative corrections for the Lorentzian EPRL spin foam propagator. We compute the amplitudes as functions of a homogeneous cutoff over the bulk quantum numbers, fixed boundary data, and different Immirzi parameters, and find that for a class of two-vertex diagrams, those with fewer than six internal faces are convergent. The calculations are done with the numerical framework sl2cfoam-next.

  1. [2206.14714] - Quasinormal ringing of regular black holes in asymptotically safe gravity: the importance of overtones - R. A. Konoplya, A. F. Zinhailo, J. Kunz, Z. Stuchlik, A. Zhidenko

  2. [2206.14249] - Effective field theories of gravity and compact binary dynamics: A Snowmass 2021 whitepaper - Walter D. Goldberger

  3. [2206.14522] - On type IIB supergravity action on $M^5 \times X^5$ solutions - S.A. Kurlyand, A.A. Tseytlin

  4. [2206.14650] - Transport coefficients associated to black holes on the brane: analysis of the shear viscosity-to-entropy density ratio - Pedro Meert

Wed - 06/29/22

There is no new related paper today

Spin-foams as semi-classical vertices: gluing constraints and a hybrid algorithm

  • Authors: Seth K. Asante, José Diogo Simão, Sebastian Steinhaus
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2206.13540
  • Abstract Numerical methods in spin-foam models have significantly advanced in the last few years, yet challenges remain in efficiently extracting results for amplitudes with many quantum degrees of freedom. In this paper we sketch a proposal for a ``hybrid algorithm’’ that would use both the full quantum amplitude and its asymptotic approximation in the relevant regimes. As a first step towards the algorithm, we derive a new representation of the partition function where each spin-foam vertex possesses its own coherent data, such that it can be individually asymptotically approximated. We do this through the implementation of gluing constraints between vertices, which we study numerically. We further derive an asymptotic expression for the constraints for arbitrary boundary data, including data for which there are no critical points. From this new representation we conjecture an intermediate quasi-geometric spin-foam regime describing a superposition of semi-classical vertices glued in a non-matching way via the gluing constraints.

  1. [2206.13940] - Generalized uncertainty principle and burning stars - H. Moradpour, A. H. Ziaie, N. Sadeghnezhad

  2. [2206.14096] - Space-time thermodynamics in momentum dependent geometries - G. Chirco, S. Liberati, J.J. Relancio

  3. [2206.13531] - Multi-instantons in minimal string theory and in matrix integrals - Dan Stefan Eniceicu, Raghu Mahajan, Chitraang Murdia, Ashoke Sen

  4. [2206.13582] - Structure constants in $\mathcal{N}=2$ superconformal quiver theories at strong coupling and holography - M. Billo, M. Frau, A. Lerda, A. Pini, P. Vallarino

  5. [2206.13736] - Locally Supersymmetric Effective Field Theories of Inflation - Hun Jang

  6. [2206.14021] - Pair Production in Non-SuSy AdS/CFT - Udit Narayan Chowdhury

Tue - 06/28/22

On a close relationship between the dressed metric and the hybrid approach to perturbations in effective loop quantum cosmology

  • Authors: Bao-Fei Li, Parampreet Singh
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
  • Arxiv link: https://arxiv.org/abs/2206.12434
  • Abstract The dressed metric and the hybrid approach to perturbations are the two main approaches to capture the effects of quantum geometry in the primordial power spectrum in loop quantum cosmology. Both consider Fock quantized perturbations over a loop quantized background and result in very similar predictions except for the modes which exit the horizon in the effective spacetime in the Planck regime. Understanding precise relationship between both approaches has so far remained obscured due to differences in construction and technical assumptions. We explore this issue at the classical and effective spacetime level for linear perturbations, ignoring backreaction, which is the level at which practical computations of the power spectrum in both of the approaches have so far been performed. We first show that at the classical level both the approaches lead to the same Hamiltonian up to the second order in perturbations and result in the same classical mass functions in the Mukhanov-Sasaki equation on the physical solutions. At the effective spacetime level, the difference in phenomenological predictions between the two approaches in the Planck regime can be traced to whether one uses the Mukhanov-Sasaki variable $Q_{\vec k}$ (the dressed metric approach) or its rescaled version $\nu_{\vec k}=aQ_{\vec k}$ (the hybrid approach) to write the Hamiltonian of the perturbations, and associated polymerization ambiguities. It turns out that if in the dressed metric approach one chooses to work with $\nu_{\vec{k}}$, the effective mass function can be written exactly as in the hybrid approach, thus leading to identical phenomenological predictions in all regimes. Our results explicitly show that the dressed metric and the hybrid approaches for linear perturbations, at a practical computational level, can be seen as two sides of the same coin.

There is no new related paper today

  1. [2206.12423] - Bouncing cosmology in modified gravity with higher-order curvature terms - J. K. Singh, Harshna Balhara, Kazuharu Bamba, J. Jena

  2. [2206.12538] - Bootstrapping the Ising Model on the Lattice - Minjae Cho, Barak Gabai, Ying-Hsuan Lin, Victor A. Rodriguez, Joshua Sandor, Xi Yin

  3. [2206.13287] - Gauge-invariant coefficients in perturbative quantum gravity - Fiorenzo Bastianelli, Roberto Bonezzi, Marco Melis

  4. [2206.13332] - Holographic Perspectives On Models Of Moduli Stabilization In M-Theory - Sirui Ning

  5. [2206.13417] - Inequalities for the holographic entanglement of purification in BCFT - Pan Li, Yi Ling

Mon - 06/27/22

There is no new related paper today

There is no new related paper today

  1. [2206.12125] - Signatures of regular black holes from the shadow of Sgr A and M87** - Indrani Banerjee, Subhadip Sau, Soumitra SenGupta

  2. [2206.12017] - Splitting-merging transitions in a tensor-vectors system in exact large-$N$ limits - Naoki Sasakura

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