15 research outputs found
Brane Decay from the Origin of Time
We present a novel scenario where matter in a spacetime originates from a
decaying brane at the origin of time. The decay could be considered as a ``Big
Bang''-like event at X^0=0. The closed string interpretation is a
time-dependent spacetime with a semi-infinite time direction, with the initial
energy of the brane converted into energy flux from the origin. The open string
interpretation can be viewed as a string theoretic non-singular initial
condition.Comment: 5 pages, 2 eps figure
Inhomogeneous Structures in Holographic Superfluids: II. Vortices
We study vortex solutions in a holographic model of Herzog, Hartnoll, and
Horowitz, with a vanishing external magnetic field on the boundary, as is
appropriate for vortices in a superfluid. We study relevant length scales
related to the vortices and how the charge density inside the core of the
vortex behaves as a function of temperature or chemical potential. We extract
the critical superfluid velocity from the vortex solutions, study how it
behaves as a function of the temperature, and compare it to earlier studies and
to the Landau criterion. We also comment on the possibility of a
Berezinskii-Kosterlitz-Thouless vortex confinement-deconfinement transition.Comment: 32 pages, 10 figures, typos corrected, references adde
The Rolling Tachyon Boundary Conformal Field Theory on an Orbifold
We consider the non-trivial boundary conformal field theory with exactly
marginal boundary deformation. In recent years this deformation has been
studied in the context of rolling tachyons and S-branes in string theory. Here
we study the problem directly from an open string point of view, at one loop.
We formulate the theory of the Z_2 reflection orbifold. To do so, we extend
fermionization techniques originally introduced by Polchinski and Thorlacius.
We also explain how to perform the open string computations at arbitrary
(rational) radius, by consistently constructing the corresponding shift
orbifold, and show in what sense these are related to known boundary states. In
a companion paper, we use these results in a cosmological context involving
decaying branes.Comment: 23 page
Inhomogeneous Structures in Holographic Superfluids I : Dark Solitons
25 pages, 17 figure files, LaTeXWe begin an investigation of inhomogeneous structures in holographic superfluids. As a first example, we study domain wall like defects in the 3+1 dimensional Einstein-Maxwell-Higgs theory, which was developed as a dual model for a holographic superconductor. In [1], we reported on such "dark solitons" in holographic superfluids. In this work, we present an extensive numerical study of their properties, working in the probe limit. We construct dark solitons for two possible condensing operators, and find that both of them share common features with their standard superfluid counterparts. However, both are characterized by two distinct coherence length scales (one for order parameter, one for charge condensate). We study the relative charge depletion factor and find that solitons in the two different condensates have very distinct depletion characteristics. We also study quasiparticle excitations above the holographic superfluid, and find that the scale of the excitations is comparable to the soliton coherence length scales.Peer reviewe
Fractional S-branes on a Spacetime Orbifold
Unstable D-branes are central objects in string theory, and exist also in
time-dependent backgrounds. In this paper we take first steps to studying brane
decay in spacetime orbifolds. As a concrete model we focus on the R^{1,d}/Z_2
orbifold. We point out that on a spacetime orbifold there exist two kinds of
S-branes, fractional S-branes in addition to the usual ones. We investigate
their construction in the open string and closed string boundary state
approach. As an application of these constructions, we consider a scenario
where an unstable brane nucleates at the origin of time of a spacetime, its
initial energy then converting into energy flux in the form of closed strings.
The dual open string description allows for a well-defined description of this
process even if it originates at a singular origin of the spacetime.Comment: 22 pages, 6 eps figure
Winding effects on brane/anti-brane pairs
We study a brane/anti-brane configuration which is separated along a compact
direction by constructing a tachyon effective action which takes into account
transverse scalars. Such an action is relevant in the study of HQCD model of
Sakai and Sugimoto of chiral symmetry breaking, where the size of the compact
circle sets the confinement scale. Our approach is motivated by string theory
orbifold constructions and gives a route to model inhomogeneous tachyon decay.
We illustrate the techniques involved with a relatively simple example of a
harmonic oscillator on a circle. We will then repeat the analysis for the
Sakai-Sugimoto model and show that by integrating out the winding modes will
provide us with a renormalized action with a lower energy than that of
truncating to zero winding sector.Comment: 21 pages, 3 figures. v3: discussion and references added, published
versio
The Taming of Closed Time-like Curves
We consider a orbifold, where acts by time and space
reversal, also known as the embedding space of the elliptic de Sitter space.
The background has two potentially dangerous problems: time-nonorientability
and the existence of closed time-like curves. We first show that closed causal
curves disappear after a proper definition of the time function. We then
consider the one-loop vacuum expectation value of the stress tensor. A naive
QFT analysis yields a divergent result. We then analyze the stress tensor in
bosonic string theory, and find the same result as if the target space would be
just the Minkowski space , suggesting a zero result for the
superstring. This leads us to propose a proper reformulation of QFT, and
recalculate the stress tensor. We find almost the same result as in Minkowski
space, except for a potential divergence at the initial time slice of the
orbifold, analogous to a spacelike Big Bang singularity. Finally, we argue that
it is possible to define local S-matrices, even if the spacetime is globally
time-nonorientable.Comment: 37 pages, LaTeX2e, uses amssymb, amsmath and epsf macros, 8 eps and 3
ps figures; (v2): Two additional comments + one reference added; (v3):
corrections in discussion of CTCs + some clarification
Topological Entanglement Entropy in Chern-Simons Theories and Quantum Hall Fluids
We compute directly the entanglement entropy of spatial regions in
Chern-Simons gauge theories in 2+1 dimensions using surgery. We use these
results to determine the universal topological piece of the entanglement
entropy for Abelian and non-Abelian quantum Hall fluids.Comment: 17 figures
Fractionalization of holographic Fermi surfaces
Zero temperature states of matter are holographically described by a
spacetime with an asymptotic electric flux. This flux can be sourced either by
explicit charged matter fields in the bulk, by an extremal black hole horizon,
or by a combination of the two. We refer to these as mesonic, fully
fractionalized and partially fractionalized phases of matter, respectively. By
coupling a charged fluid of fermions to an asymptotically AdS_4
Einstein-Maxwell-dilaton theory, we exhibit quantum phase transitions between
all three of these phases. The onset of fractionalization can be either a first
order or continuous phase transition. In the latter case, at the quantum
critical point the theory displays an emergent Lifshitz scaling symmetry in the
IR.Comment: 1+24 pages. 7 figure