35 research outputs found
Schwinger Effect and Negative Differential Conductivity in Holographic Models
The consequences of the Schwinger effect for conductivity is computed for
strong coupling systems using holography. The one loop diagram on the flavor
brane introduces an imaginary part in the effective
action for a Maxwell flavor gauge field. This in turn introduces a real
conductivity in an otherwise insulating phase of the boundary theory. Moreover
in certain regions of parameter space the differential conductivity is
negative. This is computed in the context of the Sakai-Sugimoto model
Tensionless Superstrings: View from the Worldsheet
In this brief note, we show that the residual symmetries that arise in the
analysis of the tensionless superstrings in the equivalent of the conformal
gauge is (a trivial extension of) the recently discovered 3d Super
Bondi-Metzner-Sachs algebra, discussed in the context of asymptotic symmetries
of 3d Supergravity in flat-spacetimes. This helps us uncover a limiting
approach to the construction of the tensionless superstring from the point of
view of the worldsheet, analogous to the one we had adopted earlier for the
closed tensionless bosonic string.Comment: 23 page
Inhomogeneous Tensionless Superstrings
We construct a novel tensionless limit of Superstring theory that realises
the Inhomogeneous Super Galilean Conformal Algebra (SGCA) as the residual
symmetries in the analogue of the conformal gauge, as opposed to previous
constructions of the tensionless superstring, where a smaller symmetry algebra
called the Homogeneous SGCA emerged as the residual gauge symmetry on the
worldsheet. We obtain various features of the new tensionless theory
intrinsically as well as from a systematic limit of the corresponding features
of the tensile theory. We discuss why it is desirable and also natural to work
with this new tensionless limit and the larger algebra.Comment: 34 page
Tensionless Strings from Worldsheet Symmetries
We revisit the construction of the tensionless limit of closed bosonic string
theory in the covariant formulation in the light of Galilean conformal symmetry
that rises as the residual gauge symmetry on the tensionless worldsheet. We
relate the analysis of the fundamentally tensionless theory to the tensionless
limit that is viewed as a contraction of worldsheet coordinates. Analysis of
the quantum regime uncovers interesting physics. The degrees of freedom that
appear in the tensionless string are fundamentally different from the usual
string states. Through a Bogoliubov transformation on the worldsheet, we link
the tensionless vacuum to the usual tensile vacuum. As an application, we show
that our analysis can be used to understand physics of strings at very high
temperatures and propose that these new degrees of freedom are naturally
connected with the long-string picture of the Hagedorn phase of free string
theory. We also show that tensionless closed strings behave like open strings.Comment: 40 pages; v2: references added, minor text edit