19 research outputs found
Closed String Tachyons and Their Implications for Non-Supersymmetric Strings
Closed string tachyons have long been somewhat mysterious. We note that there
is often a regime in the classical moduli space in which one can systematically
compute the effective action for such fields. In this regime, the tachyon is
light, and cannot be integrated out. Instead, one must consider the combined
dynamics of gravitons, moduli, tachyons and other light fields. We compute the
action and find that the quartic term for the tachyon is positive in the field
definition where the tachyon has no derivative coupling to the radion. We study
the evolution of isotropic, homogeneous configurations and find that typically
the system is driven to regions where the calculation is no longer under
control.Comment: 10 pages, no figures, references adde
Radion and moduli stabilization from induced brane actions in higher-dimensional brane worlds
We consider a 4+N-dimensional brane world with 2 co-dimension 1 branes in an
empty bulk. The two branes have N-1 of their extra dimensions compactified on a
sphere S^(N-1), whereas the ordinary 4 spacetime directions are Poincare
invariant. An essential input are induced stress-energy tensors on the branes
providing different tensions for the spherical and flat part of the branes. The
junction conditions - notably through their extra dimensional components - fix
both the distance between the branes as well as the size of the sphere. As a
result, we demonstrate, that there are no scalar Kaluza-Klein states at all
(massless or massive), that would correspond to a radion or a modulus field of
S^(N-1). We also discuss the effect of induced Einstein terms on the branes and
show that their coefficients are bounded from above, otherwise they lead to a
graviton ghost.Comment: 23 pages, no figures, references added, typos correcte
Hagedorn Strings and Correspondence Principle in AdS(3)
Motivated by the possibility of formulating a strings/black hole
correspondence in AdS space, we extract the Hagedorn behavior of thermal AdS_3
bosonic string from 1-loop partition function of SL(2,R) WZW model. We find
that the Hagedorn temperature is monotonically increasing as the AdS radius
shrinks, reaches a maximum of order of string scale set by the unitarity bound
of the CFT for internal space. The resulting density of states near the
Hagedorn temperature resembles the form as for strings in flat space and is
dominated by the space-like long string configurations. We then argue a
conjectured strings/black hole correspondence in AdS space by applying the
Hagedorn thermodynamics. We find the size of the corresponding black hole is a
function of the AdS radius. For large AdS radius a black hole far bigger than
the string scale will form. On the contrary, when the AdS and string scales are
comparable a string size black hole will form. We also examine strings on BTZ
background obtained through SL(2,Z) transformation. We find a tachyonic
divergence for a BTZ black hole of string scale size.Comment: 28 pages, 4 figures;v2 references added & appear on JHE
Hagedorn divergences and tachyon potential
We consider the critical behavior for a string theory near the Hagedorn
temperature. We use the factorization of the worldsheet to isolate the Hagedorn
divergences at all genera. We show that the Hagedorn divergences can be
resummed by introducing double scaling limits, which smooth the divergences.
The double scaling limits also allow one to extract the effective potential for
the thermal scalar. For a string theory in an asymptotic anti-de Sitter (AdS)
spacetime, the AdS/CFT correspondence implies that the critical Hagedorn
behavior and the relation with the effective potential should also arise from
the boundary Yang-Mills theory. We show that this is indeed the case. In
particular we find that the free energy of a Yang-Mills theory contains
``vortex'' contributions at finite temperature. Yang-Mills Feynman diagrams
with vortices can be identified with contributions from boundaries of moduli
space on the string theory side.Comment: 36 pages, 13 figures, uses harvma
Families of N=2 Strings
In a given 4d spacetime bakcground, one can often construct not one but a
family of distinct N=2 string theories. This is due to the multiple ways N=2
superconformal algebra can be embedded in a given worldsheet theory. We
formulate the principle of obtaining different physical theories by gauging
different embeddings of the same symmetry algebra in the same ``pre-theory.''
We then apply it to N=2 strings and formulate the recipe for finding the
associated parameter spaces of gauging. Flat and curved target spaces of both
(4,0) and (2,2) signatures are considered. We broadly divide the gauging
choices into two classes, denoted by alpha and beta, and show them to be
related by T-duality. The distinction between them is formulated topologically
and hinges on some unique properties of 4d manifolds. We determine what their
parameter spaces of gauging are under certain simplicity ansatz for generic
flat spaces (R^4 and its toroidal compactifications) as well as some curved
spaces. We briefly discuss the spectra of D-branes for both alpha and beta
families.Comment: 66+1 pages, 2 tables, latex 2e, hyperref. ver2: typos corrected,
reference adde
Random walks and the Hagedorn transition
We study details of the approach to the Hagedorn temperature in string theory
in various static spacetime backgrounds. We show that the partition function
for a {\it single} string at finite temperature is the torus amplitude
restricted to unit winding around Euclidean time. We use the worldsheet path
integral to derive the statement that the the sum over random walks of the
thermal scalar near the Hagedorn transition is precisely the image under a
modular transformation of the sum over spatial configurations of a single
highly excited string. We compute the radius of gyration of thermally excited
strings in . We show that the winding mode indicates an
instability despite the AdS curvature at large radius, and that the negative
mass squared decreases with decreasing AdS radius, much like the type 0
tachyon. We add further arguments to statements by Barbon and Rabinovici, and
by Adams {\it et. al.}, that the Euclidean AdS black hole can thought of as a
condensate of the thermal scalar. We use this to provide circumstantial
evidence that the condensation of the thermal scalar decouples closed string
modes.Comment: 34 pages (7 of references), 5 figures. v2: Reference added, grant
acknowledgement added, typos correcte
Electromagnetic Strings: Complementarity between Time and Temperature
We investigate some of the intricate features in a gravity decoupling limit
of a open bosonic string theory, in a constant electromagnetic (EM-) field. We
explain the subtle nature of space-time at short distances, due to its
entanglement with the gauge field windings in the theory. Incorporating the
mass-shell condition in the theory, we show that the time coordinate is small,
of the order of EM-string scale, and the space coordinates are large. We
perform a careful analysis in the critical regime to describe the decoupling of
a series of gauge-string windings in successions, just below the Hagedorn
temperature. We argue for the condensation of gauge-string at the Hagedorn
temperature, which is followed by the decoupling of tachyonic particles. We
demonstrate the phenomena by revoking the effective noncommutative dynamics for
the D(3)-brane and obtain nonlinear corrections to U(1) gauge theory. We
discuss the spontaneous breaking of noncommutative U(1) symmetry and show that
the Hagedorn phase is described by the noninteracting gauge particles. The
notion of time reappears in the phase at the expense of temperature. It
suggests a complementarity between two distinct notions, time and temperature,
at short distances.Comment: 32 pages, 2 figures, renamed title, added clarification on winding
modes, corrected typos, added reference
Area spectrum and quasinormal modes of black holes
We demonstrate that an equidistant area spectrum for the link variables in
loop quantum gravity can reproduce both the thermodynamics and the quasinormal
mode properties of black holes.Comment: 11 pages, no figures; references adde
Off-Shell Interactions for Closed-String Tachyons
Off-shell interactions for localized closed-string tachyons in C/Z_N
superstring backgrounds are analyzed and a conjecture for the effective height
of the tachyon potential is elaborated. At large N, some of the relevant
tachyons are nearly massless and their interactions can be deduced from the
S-matrix. The cubic interactions between these tachyons and the massless fields
are computed in a closed form using orbifold CFT techniques. The cubic
interaction between nearly-massless tachyons with different charges is shown to
vanish and thus condensation of one tachyon does not source the others. It is
shown that to leading order in N, the quartic contact interaction vanishes and
the massless exchanges completely account for the four point scattering
amplitude. This indicates that it is necessary to go beyond quartic
interactions or to include other fields to test the conjecture for the height
of the tachyon potential.Comment: 37 pages, 3 figures, LaTeX, JHEP class. Typos corrected, references
added, published versio
Thermodynamic behavior of IIA string theory on a pp-wave
We obtain the thermal one loop free energy and the Hagedorn temperature of
IIA superstring theory on the pp-wave geometry which comes from the circle
compactification of the maximally supersymmetric eleven dimensional one. We use
both operator and path integral methods and find the complete agreement between
them in the free energy expression. In particular, the free energy in the limit is shown to be identical with that of IIB string theory on
maximally supersymmetric pp-wave, which indicates the universal thermal
behavior of strings in the large class of pp-wave backgrounds. We show that the
zero point energy and the modular properties of the free energy are naturally
incorporated into the path integral formalism.Comment: 25 pages, Latex, JHEP style, v4: revised for clarity without change
in main contents, version to appear in JHE