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.

5 Reasons to Expect an 8 MeV Line in the SN 1987A Neutrino Spectrum

2021-08-08T07:30:20+00:00

Evidence was previously reported for an 8 MeV neutrino line associated with SN 1987A based on an analysis of 997 events recorded in the Kamiokande-II detector on the day of the supernova. That claimed line, however, occurred at the peak of the background spectrum, and both had a similar shape, making the claim tenuous at best. Here the claim is buttressed by providing five reasons to expect such an 8 MeV neutrino line. A final section of the paper concerns the ongoing KATRIN experiment to find the neutrino mass, which might provide additional support for the line, should it validate a controversial 3 + 3 model of the
neutrino masses, including a tachyonic \((m^2 < 0)\) mass.

Domain walls and M2-branes partition functions: M-theory and ABJM Theory

2021-09-26T10:01:00+00:00

We study the BPS counting functions (free energies) of the M-string configurations. We consider separated M5-branes along with M2-branes stretched between them, with M5-branes acting as domain walls interpolating different configurations of M2-branes. We find recursive structure in the free energies of these configurations.
The M-string degrees of freedom on the domain walls are interpreted in terms of a pair of interacting supersymmetric WZW models. We also compute the elliptic genus of the M-string in a toy model of the ABJM theory and compare it with the M-theory computation.

Explaining the results of EDGES observation of 21cm line with Dark Matter-Dark Energy and Dark Matter-Baryon interactions

2021-10-29T11:34:30+00:00

The EDGES experiment related to the observant of brightness temperature \(T_{21}\) of 21cm line arising from ground state of neutral Hydrogen atom, has shown an excess absorption feature ( \(− 500^ {+200}_{
− 500}\) mK) in \(T_{21}\) spectrum corresponds to the era of cosmic dawn (\(z \sim 17.2\)). In order to explain the observed excess trough of \(T_{21}\) we consider Interacting Dark Energy scenario (interaction of Dark Matter and Dark Energy) along with the scattering of baryon matter with Dark Matter. Three different Interacting Dark Energy (IDE) models are used and the viability of those models are tested in the context of EDGES experimental results. It is
found that Dark Matter-Dark Energy interaction modifies the evolution process of the Universe and hence consequently affects the brightness temperature. Dark Matter-baryon interaction also affects the \(T_{21}\) temperature since baryon fluid would transfer heat to the colder Dark Matter due to the Dark Matter baryon collision. In addition we also give bounds on the model parameters of the IDE models and Dark Matter model from EDGES observational data. It is noted that Dark Matter-Dark Energy interaction enables to explore larger range of Dark Matter mass regimes that would satisfy the EDGES result.

Formal Solutions of Any-Order Mass, Angular-Momentum, and Dipole Perturbations on the Schwarzschild Background Spacetime

2021-10-29T11:34:27+00:00

Formal solutions of any-order mass, angular-momentum, dipole perturbations on the Schwarzschild background spacetime are derived in a gauge-invariant manner. Once we accept the proposal in [K. Nakamura, Class. Quantum Grav. \({\bf 38}\) (2021), 145010.], we can extend the gauge-invariant linear perturbation theory on the Schwarzschild background spacetime including the monopole (\(l=0\)) and dipole (\(l=1\)) modes to any-order perturbations of the same background spacetime through the arguments in [K. Nakamura, Class. Quantum Grav. \({\bf 31}\) (2014), 135013.]. As a result of this resolution, we reached to a simple derivation of the above formal solutions of any order.

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.

String (In)Stability Issues with Broken Supersymmetry

2021-09-26T10:01:00+00:00

We review the main results of our investigations motivated by the tadpole potentials of ten--dimensional strings with broken supersymmetry. While these are at best partial indications, it is hard to resist the feeling that they do capture some lessons of String Theory. For example, these very tadpole potentials lead to weak-string-coupling cosmologies that appear to provide clues on the onset of the inflation from an initial fast roll. The transition, if accessible to us, would offer a natural explanation for the lack of power manifested by the CMB at large angular scales. In addition, the same tadpole potentials can drive spontaneous compactifications to lower--dimensional Minkowski spaces at corresponding length scales. Furthermore, the cosmological solutions exhibit an intriguing ``"instability of isotropy" that, if taken at face value, would point to an accidental origin of compactification. Finally, symmetric static \(AdS \times S\) solutions driven by the tadpole potentials also exist, but they are unstable due to mixings induced by their internal fluxes. On the other hand, the original Dudas--Mourad solution is perturbatively stable, and we have gathered some detailed evidence that instabilities induced by internal fluxes can be held under control in a similar class of weak--coupling type-IIB compactifications to Minkowski space.

Axion-Like Particles, Two-Higgs-Doublet Models, Leptoquarks, and the Electron and Muon \(g − 2\)

2021-08-08T08:00:31+00:00


Data from the Muon \(g − 2\) experiment and measurements of the fine structure constant suggest that the anomalous magnetic moments of the muon and electron are at odds with standard model expectations. We survey the ability of axion-like particles, two-Higgs-doublet models and leptoquarks to explain the discrepancies. We find that accounting for other constraints, all scenarios except the Type-I, Type-II and Type-Y two-Higgs-doublet models fit the data well.

\(K_S^0-K_L^0\) Asymmetries in Weak Decays of Charmed Baryons

2021-11-06T12:37:10+00:00

The \(K_S-K_L\) (SL) asymmetry occurs in the two-body charmed baryon decay with neutral kaon contained in their final states.In this work, based on the topological diagram approach and separated contributions calculated in naive factorization and the pole model, we provide explicit predictions on SL asymmetries for all the singly charmed baryon two-body decays. Especially, for the first time, we predict a sizable SL asymmetry for \(\Omega_c\) decays in its unique decay channel \(\Omega_c\to \Xi^0 K_{S,L}\). Among the four groups of decays in antitriplet charmed baryons, the \(R\) values for \(\Xi_c^+\to \Sigma^+ K_{S,L}\) and \(\Xi_c^0\to \Sigma^0 K_{S,L}\) are around \(-0.5\), which are promising to be measured. However, the other two groups \(\Lambda_c^+\to p K_{S,L}\) and \(\Xi_c^0\to \Lambda^0 K_{S,L}\) are relatively small. Our predictions are partially consistent with theoretical results provided by two other groups and an examination by future experiments is highly anticipated.