Letters in High Energy Physics

Noncommutative-Geometry Wormholes with Isotropic Pressure

2021-02-02T14:59:41+00:00

The strategy adopted in the original Morris-Thorne wormhole was to retain complete control over the geometry at the expense of certain engineering considerations. The purpose of this paper is to obtain several complete wormhole solutions by assuming a noncommutative-geometry background with a concomitant isotropic pressure condition. This condition allows us to consider a cosmological setting with a perfect-fluid equation of state. An extended form of the equation generalizes the first solution and subsequently leads to the generalized Chaplygin gas model and hence to a third solution. The solutions obtained extend several previous results. This paper also reiterates the need for a noncommutative-geometry background to account for the enormous radial tension that is a characteristic of Morris-Thorne wormholes.

Quantum Mechanics and the Continuum Limit of an Emergent Geometry

2021-06-05T02:05:25+00:00

Recent advances in emergent geometry have identified a new class of models that represent spacetime as the graph obtained as the ground state of interacting Ising spins. These models have many desirable features, including stable excitations possessing many of the characteristics of a quantum particle. We analyze the dynamics of such excitations, including a detailed treatment of the edge states not previously addressed. Using a minimal prescription for the interaction of defects we numerically investigate approximate bounds to the speed of propagation of such a “particle”. We discover, using numerical simulations, that there may be a Lieb-Robinson bound to propagation that could point the way to how a causal structure could be accommodated in this class of emergent geometry models.

Charged Wormholes in Spacetimes of Embedding Class One

2021-06-16T12:52:42+00:00

The existence of charged black holes has suggested that wormholes may also be charged. The purpose of this paper is to construct a general model of a charged wormhole that proves to be a natural extension of the original Morris-Thorne wormhole. This goal is achieved by means of the classical embedding theory that has played a major role in the general theory of relativity.

A Generally Covariant Theory of Quantized Dirac Field in de Sitter Spacetime

2021-08-02T06:54:56+00:00

As a sequel to our previous work [1], we propose in this paper a quantization scheme for Dirac field in

de Sitter spacetime. Our scheme is covariant under both general transformations and Lorentz transforma-
tions. We first present a Hamiltonian structure, then quantize the field following the standard approach

of constrained systems. For the free field, the time-dependent quantized Hamiltonian is diagonalized by
Bogliubov transformation and the eigen-states at each instant are interpreted as the observed particle states

at that instant. The measurable energy-momentum of observed particle/antiparticles are the same as ob-
tained for Klein-Gordon field. Moreover, the energy-momentum also satisfies geodesic equation, a feature

justifying its measurability. As in [1], though the mathematics is carried out in terms of conformal coordi-
nates for the sake of convenience, the whole theory can be transformed into any other coordinates based on

general covariance. It is concluded that particle/antiparticle states, such as vacuum states in particular are
time-dependent and vacuum states at one time evolves into non-vacuum states at later times. Formalism
of perturbational calculation is provided with an extended Dirac picture.

String Theory, the Dark Sector, and the Hierarchy Problem

2021-02-08T07:09:17+00:00

We discuss dark energy, dark matter, and the hierarchy problem in the context of a general noncommutative formulation of string theory. In this framework, dark energy is generated by the dynamical geometry of the dual spacetime while dark matter, on the other hand, comes from the degrees of freedom dual to the visible matter. This formulation of string theory is sensitive to both the IR and UV scales, and the Higgs scale is radiatively stable by being a geometric mean of radiatively stable UV and IR scales. We also comment on various phenomenological signatures of this novel approach to dark energy, dark matter, and the hierarchy problem. We find that this new view on the hierarchy problem is realized in a toy model based on a nonholomorphic deformation of the stringy cosmic string. Finally, we discuss a proposal for a new nonperturbative formulation of string theory, which sheds light on M-theory and F-theory, as well as on supersymmetry and holography.

Comments on Brane Recombination, Finite Flux Vacua, and the Swampland

2021-02-19T17:16:11+00:00

The Swampland program relies heavily on the conjecture that there can only be a finite number of flux vacua (FFV conjecture). Stipulating this FFV conjecture and applying it to some older work in flux vacua construction, we show that within a patch of the landscape the FFV conjecture makes predictions on the nonexistence of otherwise viable nonperturbative objects arising from brane recombination. Future gains in the direct nonperturbative analysis could, therefore, not only test this prediction but also test portions of the Swampland program itself. We also discuss implications of a weaker FFV conjecture on the counting of flux vacua which predicts the positivity of the brane central charge if the EFT analysis is to be qualitatively trusted.

de Sitter Complementarity, TCC, and the Swampland

2021-03-06T19:21:15+00:00

Motivated by the coincidence of scrambling time in de Sitter and maximum lifetime given by the Trans-Planckian Censorship Conjecture (TCC), we study the relation between the de Sitter complementarity and the Swampland conditions. We study thermalization in de Sitter space from different perspectives and show that TCC implies de Sitter space cannot live long enough to be considered a thermal background. We also revisit \(\alpha\)-vacua in light of this work and show that TCC imposes multiple initial condition/fine-tuning problems on any conventional inflationary scenario.

Trans-Planckian Censorship Conjecture and Early Universe Cosmology

2021-03-19T20:09:33+00:00

I review the Trans-Planckian Censorship Conjecture (TCC) and its implications for cosmology, in particular for the inflationary universe scenario. Whereas the inflationary scenario is tightly constrained by the TCC, alternative early universe scenarios are not restricted.