6,402 research outputs found

### Infra-red dynamics of D1-branes at the conifold

We study the infra-red dynamics of D1-branes at the conifold. We show using
methods developed to study the infra-red dynamics of (4,4) theories, the
infra-red degrees of freedom of the (2,2) theory of a single D1-brane at the
conifold is that of a linear dilaton with background charge of $\sqrt{2}$ and a
compact scalar. The gauge theory of $N$ D1-branes at the conifold is used to
formulate the matrix string in the conifold background.Comment: 20 pages, latex, some clarifications added, version to appear in JHE

### Excitations on wedge states and on the sliver

We study ghost number one excitations on the sliver to investigate the
solution of string field actions around the tachyon vacuum. The generalized
gluing and resmoothing theorem is used to develop a method for evaluating the
effective action for excitations on both the wedge states and the sliver state.
We analyze the discrete symmetries of the resulting effective action for
excitations on the sliver. The gauge unfixed effective action till level two
excitations on the sliver is evaluated. This is done for the case with the BRST
operator $c_0$ and $c_0 + (c_2 + c_{-2})/2$ with excitations purely in the
ghost sector. We find that the values of the effective potential at the local
maximum lie close by for the zeroth and the second level of approximation. This
indicates that level truncation in string field theory around the tachyon
vacuum using excitations on the sliver converges for both choices of the BRST
operator. It also provides evidence for the conjectured string field theory
actions around the tachyon vacuum.Comment: 31 pages, 1 figure, refrences added, corrected some typo

### U(1) gauge invariance from open string field theory

The naive low energy effective action of the tachyon and the U(1) gauge field
obtained from string field theory does not correspond to the world volume
action of unstable branes in bosonic string theory. We show that there exists a
field redefinition which relates the gauge field and the tachyon of the string
field theory action to the fields in the world volume action of unstable
branes. We identify a string gauge symmetry which corresponds to the U(1) gauge
transformation. This is done to the first non-linear order in the fields. We
examine the vector fluctuations at the tachyon condensate till level (4,8).Comment: Section on transverse photon at tachyon condensate added, 23 pages,
Uses JHEP.cl

### Tachyon condensation in the D0/D4 system

The D0/D4 system with a Neveu-Schwarz B-field in the spatial directions of
the D4-brane has a tachyon in the spectrum of the (0,4) strings. The tachyon
signals the instability of the system to form a bound state of the D0-brane
with the D4-brane. We use the Wess-Zumino-Witten like open superstring field
theory formulated by Berkovits to study the tachyon potential for this system.
The tachyon potential lies outside the universality class of the D-brane
anti-D-brane system. It is a function of the B-field. We calculate the tachyon
potential at the zeroth level approximation. The minimum of the tachyon
potential in this case is expected to reproduce the mass defect involved in the
formation of the D0/D4 bound state. We compare the minimum of the tachyon
potential with the mass defect in three cases. For small values of the B-field
we obtain 70% of the expected mass defect. For large values of the B-field with
Pf$(2\pi\alpha' B) >0$ the potential reduces to that of the D-brane
anti-D-brane reproducing 62% of the expected mass defect. For large values of
the B-field with Pf$(2\pi\alpha' B) <0$ the minimum of the tachyon potential
gives 25% of the expected mass defect. At the tachyon condensate we show that
the (0,4) strings decouple from the low energy dynamics.Comment: 22 pages, 2 figures, uses JHEP.cl

### Anti-de Sitter gravity associated with the supergroup $SU(1,1|2)\times SU(1,1|2)$

We construct the anti-de Sitter supergravity in three dimensions associated
with the supergroup $SU(1,1|2)\times SU(1,1|2)$. The field content and the
action are inferred using the fact that $AdS$ supergravity theories in three
dimensions are Chern-Simons theories.Comment: 8 pages, no figures, LaTe

### Gravitational couplings in ${\cal N}=2$ string compactifications and Mathieu Moonshine

We evaluate the low energy gravitational couplings, $F_g$ in the heterotic
$E_8\times E_8$ string theory compactified on orbifolds of $K3\times T^2$ by
$g'$ which acts as a $\mathbb{Z}_N$ automorphisim on $K3$ together with a $1/N$
shift along $T^2$. The orbifold $g'$ corresponds to the conjugacy classes of
the Mathieu group $M_{24}$. The holomorphic piece of $F_g$ is given in terms of
a polylogarithim with index $3-2g$ and predicts the Gopakumar-Vafa invariants
in the corresponding dual type II Calabi-Yau compactifications. We show that
low lying Gopakumar-Vafa invariants for each of these compactifications
including the twisted sectors are integers. We observe that the conifold
singularity for all these compactifications occurs only when states in the
twisted sectors become massless and the strength of the singularity is
determined by the genus zero Gopakumar-Vafa invariant at this point in the
moduli space.Comment: 54 pages, Mathematica code included in the source file, minor typos
fixed, one reference adde

### Renyi entropies of free bosons on the torus and holography

We analytically evaluate the Renyi entropies for the two dimensional free
boson CFT. The CFT is considered to be compactified on a circle and at finite
temperature. The Renyi entropies S_n are evaluated for a single interval using
the two point function of bosonic twist fields on a torus. For the case of the
compact boson, the sum over the classical saddle points results in the
Riemann-Siegel theta function associated with the A_{n-1} lattice. We then
study the Renyi entropies in the decompactification regime. We show that in the
limit when the size of the interval becomes the size of the spatial circle, the
entanglement entropy reduces to the thermal entropy of free bosons on a circle.
We then set up a systematic high temperature expansion of the Renyi entropies
and evaluate the finite size corrections for free bosons. Finally we compare
these finite size corrections both for the free boson CFT and the free fermion
CFT with the one-loop corrections obtained from bulk three dimensional
handlebody spacetimes which have higher genus Riemann surfaces as its boundary.
One-loop corrections in these geometries are entirely determined by quantum
numbers of the excitations present in the bulk. This implies that the leading
finite size corrections contributions from one-loop determinants of the
Chern-Simons gauge field and the Dirac field in the dual geometry should
reproduce that of the free boson and the free fermion CFT respectively. By
evaluating these corrections both in the bulk and in the CFT explicitly we show
that this expectation is indeed true.Comment: Published version. 56 pages. 6 figures. Argument for the agreement of
the leading finite size corrections evaluated from CFT and gravity has been
adde

### Properties of dyons in ${\cal N}=4$ theories at small charges

We study three properties of $1/4$ BPS dyons at small charges in string
compactifications which preserve ${\cal N}=4$ supersymmetry. We evaluate the
non-trivial constant present in the one loop statistical entropy for ${\cal
N}=4$ compactifications of type IIB theory on $K3\times T^2$ orbifolded by an
order $\mathbb{Z}_N$ freely acting orbifold $g'$ including all CHL
compactifications. This constant is trivial for the un-orbifolded model but we
show that it contributes crucially to the entropy of low charge dyons in all
the orbifold models. We then show that the meromorphic Jacobi form which
captures the degeneracy of $1/4$ BPS states for the first two non-trivial
magnetic charges can be decomposed into an Appell-Lerch sum and a mock Jacobi
form transforming under $\Gamma_0(N)$. This generalizes the earlier observation
of Dabholkar-Murthy-Zagier to the orbifold models. Finally we study the sign of
the Fourier coefficients of the inverse Siegel modular form which counts the
index of $1/4$ BPS dyons in ${\cal N}=4$ models obtained by freely acting
$\mathbb{Z}_2$ and $\mathbb{Z}_3$ orbifolds of type II theory compactified on
$T^6$. We show that sign of the index for sufficiently low charges and ensuring
that it counts single centered black holes, violates the positivity conjecture
of Sen which indicates that these states posses non-trivial hair

### Supersymmetry of classical solutions in Chern-Simons higher spin supergravity

We construct and study classical solutions in Chern-Simons supergravity based
on the superalgebra sl(N|N-1). The algebra for the N=3 case is written down
explicitly using the fact that it arises as the global part of the super
conformal W_3 superalgebra. For this case we construct new classical solutions
and study their supersymmetry. Using the algebra we write down the Killing
spinor equations and explicitly construct the Killing spinor for conical
defects and black holes in this theory. We show that for the general sl(N|N-1)
theory the condition for the periodicity of the Killing spinor can be written
in terms of the products of the odd roots of the super algebra and the
eigenvalues of the holonomy matrix of the background. Thus the supersymmetry of
a given background can be stated in terms of gauge invariant and well defined
physical observables of the Chern-Simons theory. We then show that for N\geq 4,
the sl(N|N-1) theory admits smooth supersymmetric conical defects.Comment: 40 pages, includes discussion of conical defects for N\geq 4, typos
corrected and presentation improve

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