SciPost Physics Proceedings

SciPost Physics Proceedings issue 4

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• Properties of non-relativistic string theory

  E.A. Bergshoeff, J. Lahnsteiner, L. Romano, C. Simsek

  SciPost Phys. Proc. 4, 001 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We show how Newton-Cartan geometry can be generalized to String Newton-Cartan geometry which is the geometry underlying non-relativistic string theory. Several salient properties of non-relativistic string theory in this geometric background are presented and a discussion of possible research for the future is outlined.

• De Sitter entropy as holographic entanglement entropy

  Nikolaos Tetradis

  SciPost Phys. Proc. 4, 002 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We review the results of refs. [1, 2], in which the entanglement entropy in spaces with horizons, such as Rindler or de Sitter space, is computed using holography. This is achieved through an appropriate slicing of anti-de Sitter space and the implementation of a UV cutoff. When the entangling surface coincides with the horizon of the boundary metric, the entanglement entropy can be identified with the standard gravitational entropy of the space. For this to hold, the effective Newton’s constant must be defined appropriately by absorbing the UV cutoff. Conversely, the UV cutoff can be expressed in terms of the effective Planck mass and the number of degrees of freedom of the dual theory. For de Sitter space, the entropy is equal to the Wald entropy for an effective action that includes the higher-curvature terms associated with the conformal anomaly. The entanglement entropy takes the expected form of the de Sitter entropy, including logarithmic corrections.

• From Rindler fluid to dark fluid on the holographic cutoff surface

  Rong-Gen Cai, Gansukh Tumurtushaa, Yun-Long Zhang

  SciPost Phys. Proc. 4, 003 (2021) · published 13 August 2021 | Toggle abstract · pdf

  As an approximation to the near horizon regime of black holes, the Rindler fluid was proposed on an accelerating cutoff surface in the flat spacetime. The concept of the Rindler fluid was then generalized into a flat bulk with the cutoff surface of the induced de Sitter and FRW universe, such that an effective description of dark fluid in the accelerating universe can be investigated.

• Two faces of Hawking radiation and thin-shell emission: pair-creation vs. tunneling

  Dong-han Yeom

  SciPost Phys. Proc. 4, 004 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We first revisit Hartle and Hawking's path integral derivation of Hawking radiation. In the first point of view, we interpret that a particle-antiparticle pair is created and the negative energy antiparticle falls into the black hole. On the other point of view, a particle inside the horizon, or beyond the Einstein-Rosen bridge, tunnels to outside the horizon, where this computation requires the analytic continuation of the time. These two faces of the Hawking radiation process can be extended to not only particles but also fields. As a concrete example, we study the thin-shell tunneling process; by introducing the antishell as a negative tension shell, we can give the consistent interpretation for two pictures, where one is a tunneling from inside to outside the horizon using instantons, while the other is a shell-antishell pair-creation. This shows that the Euclidean path integral indeed carries vast physical implications not only for perturbative, but also for non-perturbative processes.

• Charges in the extended BMS algebra: Definitions and applications

  Massimo Porrati

  SciPost Phys. Proc. 4, 005 (2021) · published 13 August 2021 | Toggle abstract · pdf

  This is a review of selected topics from recent work on symmetry charges in asymptotically flat spacetime done by the author in collaboration with U. Kol and R. Javadinezhad. First we reinterpret the reality constraint on the boundary graviton as the gauge fixing of a new local symmetry, called dual supertranslations. This symmetry extends the BMS group and bears many similarities to the dual (magnetic) gauge symmetry of electrodynamics. We use this new gauge symmetry to propose a new description of the TAUB-NUT space that does not contain closed time-like curves. Next we summarize progress towards the definition of Lorentz and super-Lorentz charges that commute with supertranslations and with the soft graviton mode.

• A sharp transition in quantum chaos and thermodynamics of mass deformed SYK model

  Tomoki Nosaka

  SciPost Phys. Proc. 4, 006 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We review our recent work [arXiv:2009.10759] where we studied the chaotic property of the two coupled Sachdev-Ye-Kitaev systems exhibiting a Hawking-Page like phase transition. By computing the out-of-time-ordered correlator in the large N limit by using the bilocal field formalism, we found that the chaos exponent of this model shows a discontinuous fall-off at the phase transition temperature. Hence in this model the Hawking-Page like transition is correlated with a transition in chaoticity, as expected from the relation between a black hole geometry and the chaotic behavior in the dual field theory.

• Analogous Hawking radiation in butterfly effect

  Takeshi Morita

  SciPost Phys. Proc. 4, 007 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We propose that Hawking radiation-like phenomena may be observed in systems that show butterfly effects. Suppose that a classical dynamical system has a Lyapunov exponent $\lambda_L$, and is deterministic and non-thermal ($T=0$). We argue that, if we quantize this system, the quantum fluctuations may imitate thermal fluctuations with temperature $T \sim \hbar \lambda_L/2 \pi $ in a semi-classical regime, and it may cause analogous Hawking radiation. We also discuss that our proposal may provide an intuitive explanation of the existence of the bound of chaos proposed by Maldacena, Shenker and Stanford.

• Superradiant instability and black resonators in AdS

  Takaaki Ishii

  SciPost Phys. Proc. 4, 008 (2021) · published 13 August 2021 | Toggle abstract · pdf

  Rapidly rotating Myers-Perry-AdS black holes are unstable against rotational superradiance. From the onset of the instability, cohomogeneity-1 black resonators are constructed in five-dimensional asymptotically AdS space. By using the cohomogeneity-1 metric, perturbations of the cohomogeneity-1 black resonators are also studied.

• Position-dependent mass quantum systems and ADM formalism

  Davood Momeni

  SciPost Phys. Proc. 4, 009 (2021) · published 13 August 2021 | Toggle abstract · pdf

  The classical Einstein-Hilbert (EH) action for general relativity (GR) is shown to be formally analogous to the classical system with position-dependent mass (PDM) models. The analogy is developed and used to build the covariant classical Hamiltonian as well as defining an alternative phase portrait for GR. The set of associated Hamilton's equations in the phase space is presented as a first-order system dual to the Einstein field equations. Following the principles of quantum mechanics, I build a canonical theory for the classical general. A fully consistent quantum Hamiltonian for GR is constructed based on adopting a high dimensional phase space. It is observed that the functional wave equation is timeless. As a direct application, I present an alternative wave equation for quantum cosmology. In comparison to the standard Arnowitt-Deser-Misner(ADM) decomposition and quantum gravity proposals, I extended my analysis beyond the covariant regime when the metric is decomposed into the 3+1 dimensional ADM decomposition. I showed that an equal dimensional phase space can be obtained if one applies ADM decomposed metric.

• Hawking flux of 4D Schwarzschild blackhole with supertransition correction to second-order

  Shingo Takeuchi

  SciPost Phys. Proc. 4, 010 (2021) · published 13 August 2021 | Toggle abstract · pdf

  Former part of this article is the proceeding for my talk on arXiv:2004.07474, which is a report on the issue in the title of this article. Later part is the detailed description of arXiv:2004.07474.

• Classical boundary field theory of Jacobi sigma models by Poissonization

  Ion V. Vancea

  SciPost Phys. Proc. 4, 011 (2021) · published 13 August 2021 | Toggle abstract · pdf

  In this paper, we are going to construct the classical field theory on the boundary of the embedding of $\mathbb{R} \times S^{1}$ into the manifold $M$ by the Jacobi sigma model. By applying the poissonization procedure and by generalizing the known method for Poisson sigma models, we express the fields of the model as perturbative expansions in terms of the reduced phase space of the boundary. We calculate these fields up to the second order and illustrate the procedure for contact manifolds.

• Linear stability of Einstein and de Sitter universes in the quadratic theory of modified gravity

  Mudhahir Al-Ajmi

  SciPost Phys. Proc. 4, 012 (2021) · published 13 August 2021 | Toggle abstract · pdf

  We consider the Einstein static and the de Sitter universe solutions and examine their instabilities in a subclass of quadratic modified theories for gravity. This modification proposed by Nash is an attempt to generalize general relativity. Interestingly, we discover that the Einstein static universe is unstable in the context of the modified gravity. In contrast to Einstein static universe, the de Sitter universe remains stable under metric perturbation up to the second order.

• Area law and OPE blocks in conformal field theory

  Jiang Long

  SciPost Phys. Proc. 4, 013 (2021) · published 13 August 2021 | Toggle abstract · pdf

  This is an introduction to the relationship between area law and OPE blocks in conformal field theory.

• Why space could be quantised on a different scale to matter

  Matthew J. Lake

  SciPost Phys. Proc. 4, 014 (2021) · published 13 August 2021 | Toggle abstract · pdf

  The scale of quantum mechanical effects in matter is set by Planck's constant, $\hbar$. This represents the quantisation scale for material objects. In this article, we present a simple argument why the quantisation scale for space, and hence for gravity, may not be equal to $\hbar$. Indeed, assuming a single quantisation scale for both matter and geometry leads to the `worst prediction in physics', namely, the huge difference between the observed and predicted vacuum energies. Conversely, assuming a different quantum of action for geometry, $\beta \ll \hbar$, allows us to recover the observed density of the Universe. Thus, by measuring its present-day expansion, we may in principle determine, empirically, the scale at which the geometric degrees of freedom should be quantised.