A simple description of holographic domain walls in confining theories — extended hydrodynamics

In the context of theories with a first order phase transition, we propose a general covariant description of coexisting phases separated by domain walls using an additional order parameter-like degree of freedom. In the case of a holographic Witten model with a confining and deconfined phase, the resulting model extends hydrodynamics and has a simple formulation in terms of a spacetime action with corresponding expressions for the energy-momentum tensor. The proposed description leads to simple analytic profiles of domain walls, including expressions for surface tension density, which agree nicely with holographic numerical solutions, despite the apparent complexity of those gravitational backgrounds.

Relativistic modeling of atmospheric occultations with time transfer functions

Context. Occultation experiments represent unique opportunities to remotely probe the physical properties of atmospheres. The data processing involved in modeling the time and frequency transfers of an electromagnetic signal requires that refractivity be properly accounted for. On theoretical grounds, little work has been done concerning the elaboration of a covariant approach for modeling occultation data. Aims. We present an original method allowing fully analytical expressions to be derived up to the appropriate order for the covariant description of time and frequency transfers during an atmospheric occultation experiment. Methods. We make use of two independent powerful relativistic theoretical tools, namely the optical metric and the time transfer functions formalism. The former allows us to consider refractivity as spacetime curvature while the latter is used to determine the time and frequency transfers occurring in a curved spacetime. Results. We provide the integral form of the time transfer function up to any post-Minkowskian order. The discussion focuses on the stationary optical metric describing an occultation by a steadily rotating and spherically symmetric atmosphere. Explicit analytical expressions for the time and frequency transfers are provided at the first post-Minkowskian order and their accuracy is assessed by comparing them to results of a numerical integration of the equations for optical rays. Conclusions. The method accurately describes vertical temperature gradients and properly accounts for the light-dragging effect due to the motion of the optical medium. It can be pushed further in order to derive the explicit form of the time transfer function at higher order and beyond the spherical symmetry assumption.

A worldsheet perspective on heterotic T-duality orbifolds

Asymmetric heterotic orbifolds are discussed from the worldsheet perspective. Starting from Buscher’s gauging of a theory of D compact bosons the duality covariant description of Tseytlin is obtained after a non-Lorentz invariant gauge fixing. A left-over of the gauge symmetry can be used to removed the doubled constant zero modes so that D physical target space coordinate remain. This can be thought of as the worldsheet realization of the strong constraint of double field theory. The extension of this description to the heterotic theory is straightforward as all results are written in terms of the invariant and the generalized metrics. An explicit method is outline how to obtain a generalized metric which is invariant under T-duality orbifold actions. It is explicitly shown how shift orbifolds lead to redefinitions of the Narain moduli. Finally, a number of higher dimensional T-folds are constructed including a novel asymmetric ℤ6 orbifold.

Another Field to the Pot

This chapter focuses on the impact of field quantization methods on the problem of quantum gravity. It is shown that much work after 1930 until mid-century was an exercise in ‘exploring the consequences’ of the Heisenberg-Pauli theory of quantum electrodynamics: understanding the symmetries and the divergences, and attempting to find ways of dealing with both. The goal was very much to treat all fields in much the same way, and so one could also envisage learning about one field from another. However, there was a separate track, superficially similar, though issuing from a desire to have a theory of gravitation more in line with the rest of physics, and in particular one not involving the difficulties of curved, dynamical spacetime. The interaction representation and a desire for a manifestly covariant description played a crucial role in the development of such approaches, and involved a curious borrowing of concepts often associated with canonical approaches. An apparently orthogonal approach developed alongside these later manifestly covariant approaches, involving a hybrid approach retaining a classical gravitational field, albeit still coupled to quantized sources through the Einstein field equations. These were done largely to avoid complications, however, and the conceptual consequences, though hinted at, were not further explored.

Gauge covariant approach to the electroweak interactions of mesons in the Nambu–Jona-Lasinio model with spin-1 states

An extended Nambu–Jona-Lasinio (NJL) model with chiral group [Formula: see text] and spin-0 and spin-1 four quark interactions is used to develop the gauge covariant approach to the diagonalization of the [Formula: see text] mixing in the presence of electroweak forces. This allows for manifestly gauge covariant description of both the non-anomalous and anomalous parts of the effective Lagrangian. It is shown that in the non-anomalous sector the theory is equivalent to the standard non-covariant approach.

U-Dualities in Type II and M-Theory: A Covariant Approach

In this review, a short description of exceptional field theory and its application is presented. Exceptional field theories provide a U-duality covariant description of supergravity theories, allowing addressing relevant phenomena, such as non-geometricity. Some applications of the formalism are briefly described.

Some remarks on the Bel-Robinson tensor and gravitational radiation

The asymptotic form of the Bel-Robinson tensor in the gravitational radiation-zone is obtained in terms of the mass quadrupole of the source.A comparison is made with the standard formula for the gravitational power emission. The problem of a fully covariant description of gravitational radiation in terms of this tensor is briefly discussed.