LREE of an unstable dressed-dynamical Dp-brane: superstring calculations

We obtain the left-right entanglement entropy (LREE) for a Dp-brane with tangential motion in the presence of a U(1) gauge potential, the Kalb–Ramond field and an open string tachyon field. Thus, at first we extract the Rényi entropy and then by taking a special limit of it we acquire the entanglement entropy. We shall investigate the behavior of the LREE under the tachyon condensation phenomenon. We observe that the deformation of the LREE, through this process, reveals the collapse of the brane. Besides, we examine the second law of thermodynamics for the LREE under tachyon condensation, and we extract the imposed constraints. Note that our calculations will be in the context of the type IIA/IIB superstring theories.

Relativistic charged sphere in f(G,T) gravity

This study explores the interior geometry of static relativistic charged spheres in the background of a recently proposed modified [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] are the Gauss–Bonnet (GB) invariant and trace of energy–momentum tensor, respectively. The GB gravity is the low-energy limit of superstring theories. The structures of specific relativistic charged spheres Vela [Formula: see text], [Formula: see text], and [Formula: see text] are studied in this theory of gravity. We analyzed several physical behaviors of these relativistic charged spheres with the help of observational data and investigated the various aspects like density profile, stresses, the distribution of charges, stability, etc.

All-order quartic couplings in highly symmetric D-brane-anti-D-brane systems

We compute six-point string amplitudes for the scattering of one closed string Ramond-Ramond state, two tachyons and two gauge fields in the worldvolume of D-brane-anti-D-brane systems in the Type II superstring theories. From the resulting S-matrix elements, we read off the precise form of the couplings, including their exact numerical coefficients, of two tachyons and two gauge fields in the corresponding highly symmetric effective field eheory (EFT) Lagrangian in the worldvolume of D-brane-Anti-D-brane to all orders in α′, which modify and complete previous proposals. We verify that the EFT reproduces the infinite collection of stringy gauge field singularities in dual channels. Inspired by interesting similarities between the all-order highly symmetric EFTs and holographic duals of Vasiliev’s higher spin gravities à là Nilsson and Vasiliev, we make a proposal for tensionless limits of D-brane-anti-D-brane systems.

Stringy tachyonic instabilities of non-supersymmetric Ricci flat backgrounds

Superstring/M-theory compactified on compact Ricci flat manifolds have recently been conjectured to exhibit instabilities whenever the metrics do not have special holonomy. We use worldsheet conformal field theory to investigate instabilities of Type II superstring theories on compact, Ricci flat, spin 3-manifolds including a worldsheet description of their spin structures. The instabilities are signalled by the appearance of stringy tachyons at small radius and a negative (1-loop) vacuum energy density at large radius. We briefly discuss the extension to higher dimensions.

Five-brane current algebras in type II string theories

We study the current algebras of the NS5-branes, the Kaluza-Klein (KK) five-branes and the exotic $$ {5}_2^2 $$ 5 2 2 -branes in type IIA/IIB superstring theories. Their worldvolume theories are governed by the six-dimensional $$ \mathcal{N} $$ N = (2, 0) tensor and the $$ \mathcal{N} $$ N = (1, 1) vector multiplets. We show that the current algebras are determined through the S- and T-dualities. The algebras of the $$ \mathcal{N} $$ N = (2, 0) theories are characterized by the Dirac bracket caused by the self-dual gauge field in the five-brane worldvolumes, while those of the $$ \mathcal{N} $$ N = (1, 1) theories are given by the Poisson bracket. By the use of these algebras, we examine extended spaces in terms of tensor coordinates which are the representation of ten-dimensional supersymmetry. We also examine the transition rules of the currents in the type IIA/IIB supersymmetry algebras in ten dimensions. Based on the algebras, we write down the section conditions in the extended spaces and gauge transformations of the supergravity fields.

Surface terms in effective action of O-plane at order $$\alpha '^2$$

The effective action of string theory has both bulk and boundary terms if the spacetime is an open manifold. Recently, the known classical effective action of string theory at the leading order of $$\alpha '$$ α ′ and its corresponding boundary action have been reproduced by constraining the effective actions to be invariant under gauge transformations and under string duality transformations. In this paper, we use this idea to find the classical effective action of the O-plane and its corresponding boundary terms in type II superstring theories at order $$\alpha '^2$$ α ′ 2 and for NS–NS couplings. We find that these constraints fix the bulk action and its corresponding boundary terms up to one overall factor. They also produce three multiplets in the boundary action that their coefficients are independent of the bulk couplings under the string dualities.

Effective action of type II superstring theories at order α′3: NS-NS couplings

Recently, it has been shown that the minimum number of gauge invariant couplings for B-field, metric and dilaton at order α′3 is 872. These couplings, in a particular scheme, appear in 55 different structures. In this paper, up to an overall factor, we fix all parameters in type II supertirng theories by requiring the reduction of the couplings on a circle to be invariant under T-duality transformations. We find that there are 445 non-zero couplings which appear in 15 different structures. The couplings are fully consistent with the partial couplings that have been found in the literature by the four-point S-matrix element and by the non-linear Sigma model methods.

Alignments and Gaps Between Multi-fold Universes And Loop Quantum Gravity

Multi-fold universes and LQG have a lot in common as well as complementarities. A priori, both models are compatible with each other. The present paper analyses these touch points and suggests ways forward both in terms of multi-fold universes and of LQG. Also, considering the relationships between multi-fold universes results and superstring theories, there are many ways that the three approaches could use lessons learned or mechanisms from each other, in order to fill gaps or improve some of their own models. Maybe they could even converge towards new and more encompassing combined frameworks. We conclude with a call for such a collaboration.

String geometry and nonperturbative formulation of string theory

We define string geometry: spaces of superstrings including the interactions, their topologies, charts, and metrics. Trajectories in asymptotic processes on a space of strings reproduce the right moduli space of the super-Riemann surfaces in a target manifold. Based on the string geometry, we define Einstein–Hilbert action coupled with gauge fields, and formulate superstring theory nonperturbatively by summing over metrics and the gauge fields on the spaces of strings. This theory does not depend on backgrounds. The theory has a supersymmetry as a part of the diffeomorphisms symmetry on the superstring manifolds. We derive the all-order perturbative scattering amplitudes that possess the super moduli in type IIA, type IIB and SO(32) type I superstring theories from the single theory, by considering fluctuations around fixed backgrounds representing type IIA, type IIB and SO(32) type I perturbative vacua, respectively. The theory predicts that we can see a string if we microscopically observe not only a particle but also a point in the space–time. That is, this theory unifies particles and the space–time. This paper is a summary version of Ref. 1.

Phantom wormhole solutions in a generic cosmological constant background

There are a number of reasons to study wormholes with generic cosmological constant Λ. Recent observations indicate that the present accelerating expansion of the universe demands Λ > 0. On the other hand, some extended theories of gravitation, such as supergravity and superstring theories, possess vacuum states with Λ < 0. Even within the framework of general relativity, a negative cosmological constant permits black holes with horizons topologically different from the usual spherical ones. These solutions are convertible to wormhole solutions by adding some exotic matter. In this paper, the asymptotically flat wormhole solutions in a generic cosmological constant background are studied. By constructing a specific class of shape functions, a mass function, energy density, and pressure profile that support such a geometry are obtained. It is shown that for having such a geometry, the wormhole throat, r0, the cosmological constant, Λ, and the equation of state parameter, ω, should satisfy two specific conditions. The possibility of setting different values for the parameters of the model helps us to find exact solutions for the metric functions, mass functions, and energy–momentum profiles. At last, the volume integral quantifier, which provides useful information about the total amount of energy-condition violating matter, is discussed briefly.