97 research outputs found
Quantization and Scattering in the IIB SL(2,Z) Covariant Superstring
We rewrite the SL(2,Z) covariant worldsheet action for the IIB string
proposed by Townsend in a Polyakov form. In a flat background the formalism
yields separate (p,q) sectors. In each one the action is that of the IIB string
action with the string slope parameter \alp\pr replaced by its SL(2,Z) analogue
\alp_{pq}\pr. SL(2,Z) invariant graviton scattering amplitudes are obtained
from those of the fundamental (1,0) string by summing over the different
sectors. The tree-level four-graviton amplitude in this formalism differs from
a previously conjectured non-perturbative form; both yield the same expansion
in order \alpha\pr^3.Comment: 15 pages, LaTeX, additional comment
General covariance of the non-abelian DBI-action
In this paper we study the action for N D0-branes in a curved background. In
particular, we focus on the meaning of space-time diffeomorphism invariance.
For a single D-brane, diffeomorphism invariance acts in a naive way on the
world-volume fields, but for multiple D-branes, the meaning of diffeomorphism
invariance is much more obscure. The problem goes beyond the determination of
an ordering of the U(N)-valued fields, because one can show that there is no
lift of ordinary diffeomorphisms to matrix-valued diffeomorphisms. On the other
hand, the action can presumably be constructed from perturbative string theory
calculations. Based on the general characteristics of such calculations we
determine a set of constraints on the action for N D0-branes, that ensure
space-time covariance. These constraints can be solved order by order, but they
are insufficient to determine the action completely. All solutions to the
constraints obey the axioms of D-geometry. Moreover the action must contain new
terms. This exhibits clearly that the answer is more than a suitable ordering
of the action of a single D0 brane.Comment: latex, 38 page
Crosscaps in Gepner Models and the Moduli space of T2 Orientifolds
We study T^2 orientifolds and their moduli space in detail. Geometrical
insight into the involutive automorphisms of T^2 allows a straightforward
derivation of the moduli space of orientifolded T^2s. Using c=3 Gepner models,
we compare the explicit worldsheet sigma model of an orientifolded T^2
compactification with the CFT results. In doing so, we derive
half-supersymmetry preserving crosscap coefficients for generic unoriented
Gepner models using simple current techniques to construct the charges and
tensions of Calabi-Yau orientifold planes. For T^2s we are able to identify the
O-plane charge directly as the number of fixed points of the involution; this
number plays an important role throughout our analysis. At several points we
make connections with the mathematical literature on real elliptic curves. We
conclude with a preliminary extension of these results to elliptically fibered
K3s.Comment: LaTeX, 59 pages, 21 figures (uses axodraw
Two-point function of a quantum critical metal in the limit , with fixed
We show that the fermionic and bosonic spectrum of fermions at finite
density coupled to a critical boson can be determined non-perturbatively in the
combined limit , with
fixed. In this double scaling limit, the boson two-point function is corrected,
but only at one-loop. This double scaling limit therefore incorporates the
leading effect of Landau damping. The fermion two-point function is determined
analytically in real space and numerically in (Euclidean) momentum space. The
resulting spectrum is discontinuously connected to the quenched result. For with fixed the spectrum exhibits the
distinct non-Fermi-liquid behavior previously surmised from the RPA
approximation. However, the exact answer obtained here shows that the RPA
result does not fully capture the IR of the theory.Comment: 37 pages, 10 figure
Hydrodynamic charge and heat transport on inhomogeneous curved spaces
We develop the theory of hydrodynamic charge and heat transport in strongly
interacting quasi-relativistic systems on manifolds with inhomogeneous spatial
curvature. In solid-state physics, this is analogous to strain disorder in the
underlying lattice. In the hydrodynamic limit, we find that the thermal and
electrical conductivities are dominated by viscous effects, and that the
thermal conductivity is most sensitive to this disorder. We compare the effects
of inhomogeneity in the spatial metric to inhomogeneity in the chemical
potential, and discuss the extent to which our hydrodynamic theory is relevant
for experimentally realizable condensed matter systems, including suspended
graphene at the Dirac point.Comment: 15+8 pages, 4+1 figures; v2: added references, published versio
Pairing induced superconductivity in holography
We study pairing induced superconductivity in large strongly coupled
systems at finite density using holography. In the weakly coupled dual
gravitational theory the mechanism is conventional BCS theory. An IR hard wall
cut-off is included to ensure that we can controllably address the dynamics of
a single confined Fermi surface. We address in detail the interplay between the
scalar order parameter field and fermion pairing. Adding an explicitly
dynamical scalar operator with the same quantum numbers as the fermion-pair,
the theory experiences a BCS/BEC crossover controlled by the relative scaling
dimensions. We find the novel result that this BCS/BEC crossover exposes
resonances in the canonical expectation value of the scalar operator. This
occurs not only when the scaling dimension is degenerate with the Cooper pair,
but also with that of higher derivative paired operators. We speculate that a
proper definition of the order parameter which takes mixing with these
operators into account stays finite nevertheless.Comment: 38 pages; 24 figures; revtex4 v2: Acknowledgements adde
Correlating correlation functions of primordial perturbations
We explore the correlations between correlation functions of the primordial
curvature perturbation produced during inflation. We find that for general
single field inflation, other than the source terms which depend on the model
details, higher order correlation functions are characterized by the power
spectrum, its spectral index and running. The correlation between the
bispectrum and power spectrum is presented as an explicit example of our
systematic approach.Comment: (v1) 8 pages, 1 figure; (v2) references added and typos corrected, to
appear in Physical Review
Dynamical Topology Change in M Theory
We study topology change in M theory compactifications on Calabi-Yau
three-folds in the presence of G flux (the four form field strength). In
particular, we discuss vacuum solutions in strongly coupled heterotic string
theory in which the topology change is inevitable within a single spacetime
background. For rather generic choices of initial conditions, the field
equations drive the Kahler moduli outside the classical moduli space of a
Calabi-Yau manifold. Consistency of the solution suggests that degenerate flop
curves - just as wrapped M theory fivebranes - carry magnetic charges under the
four form field strength.Comment: 21 pages, LaTeX, 2 figures (eps
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