3,692 research outputs found
A brief review of "little string theories"
This is a brief review of the current state of knowledge on "little string
theories", which are non-gravitational theories having several string-like
properties. We focus on the six dimensional maximally supersymmetric "little
string theories" and describe their definition, some of their simple
properties, the motivations for studying them, the DLCQ and holographic
constructions of these theories and their behaviour at finite energy density.
(Contribution to the proceedings of Strings '99 in Potsdam, Germany.)Comment: 11 pages, contribution to Strings '99 proceeding
The effective string spectrum in the orthogonal gauge
The low-energy effective action on long string-like objects in quantum field
theory, such as confining strings, includes the Nambu-Goto action and then
higher-derivative corrections. This action is diffeomorphism-invariant, and can
be analyzed in various gauges. Polchinski and Strominger suggested a specific
way to analyze this effective action in the orthogonal gauge, in which the
induced metric on the worldsheet is conformally equivalent to a flat metric.
Their suggestion leads to a specific term at the next order beyond the
Nambu-Goto action. We compute the leading correction to the Nambu-Goto spectrum
using the action that includes this term, and we show that it agrees with the
leading correction previously computed in the static gauge. This gives a
consistency check for the framework of Polchinski and Strominger, and helps to
understand its relation to the theory in the static gauge.Comment: 21 page
Stable Non-Supersymmetric Supergravity Solutions from Deformations of the Maldacena-Nunez Background
We study a deformation of the type IIB Maldacena-Nunez background which
arises as the near-horizon limit of NS5 branes wrapped on a two-cycle. This
background is dual to a "little string theory" compactified on a two-sphere, a
theory which at low energies includes four-dimensional N = 1 super Yang-Mills
theory. The deformation we study corresponds to a mass term for some of the
scalar fields in this theory, and it breaks supersymmetry completely. In the
language of seven-dimensional SO(4) gauged supergravity the deformation
involves (at leading order) giving a VEV, depending only on the radial
coordinate, to a particular scalar field. We explicitly construct the
corresponding solution at leading order in the deformation, both in
seven-dimensional and in ten-dimensional supergravity, and we verify that it
completely breaks supersymmetry. Since the original background had a mass gap
and we are performing a small deformation, the deformed background is
guaranteed to be stable even though it is not supersymmetric.Comment: 1+31 pages, one figure. v2: minor clarifications, refs adde
c=1 String Theory as a Topological G/G Model
The physical states on the free field Fock space of the {SL(2,R)\over
SL(2,R) model at any level are computed. Using a similarity transformation on
, the cohomology of the latter is mapped into a direct sum of simpler
cohomologies. We show a one to one correspondence between the states of the
model and those of the string model. A full equivalence between
the {SL(2,R)\over SL(2,R) and {SL(2,R)\over U(1) models at the level of
their Fock space cohomologies is found.Comment: 19
On jet quenching parameters in strongly coupled non-conformal gauge theories
Recently Liu, Rajagopal and Wiedemann (LRW) [hep-ph/0605178] proposed a first
principle, nonperturbative quantum field theoretic definition of ``jet
quenching parameter'' \hat{q} used in models of medium-induced radiative parton
energy loss in nucleus-nucleus collisions at RHIC. Relating \hat{q} to a
short-distance behavior of a certain light-like Wilson loop, they used gauge
theory-string theory correspondence to evaluate \hat{q} for the strongly
coupled N=4 SU(N_c) gauge theory plasma. We generalize analysis of LRW to
strongly coupled non-conformal gauge theory plasma. We find that a jet
quenching parameter is gauge theory specific (not universal). Furthermore, it
appears it's value increases as the number of effective adjoint degrees of
freedom of a gauge theory plasma increases.Comment: 14 pages, latex; v2: PRD versio
"Double-trace" Deformations, Boundary Conditions and Spacetime Singularities
Double-trace deformations of the AdS/CFT duality result in a new perturbation
expansion for string theory, based on a non-local worldsheet. We discuss some
aspects of the deformation in the low energy gravity approximation, where it
appears as a change in the boundary condition of fields. We relate unique
features of the boundary of AdS to the worldsheet becoming non-local, and
conjecture that non-local worldsheet actions may be generic in other classes of
backgrounds.Comment: 21 pages, 2 figures, harvmac. v2: minor changes, references added,
version sent to JHEP. v3 minor correction
A first order deconfinement transition in large N Yang-Mills theory on a small 3-sphere
We give an analytic demonstration that the 3+1 dimensional large N SU(N) pure
Yang-Mills theory, compactified on a small 3-sphere so that the coupling
constant at the compactification scale is very small, has a first order
deconfinement transition as a function of temperature. We do this by explicitly
computing the relevant terms in the canonical partition function up to 3-loop
order; this is necessary because the leading (1-loop) result for the phase
transition is precisely on the borderline between a first order and a second
order transition. Since numerical work strongly suggests that the infinite
volume large N theory also has a first order deconfinement transition, we
conjecture that the phase structure is independent of the size of the 3-sphere.
To deal with divergences in our calculations, we are led to introduce a novel
method of regularization useful for nonabelian gauge theory on a 3-sphere.Comment: 63 pages (40 pages + 2 appendices), 6 figures, harvmac. v2: minor
correction
Comment on "Bicritical and Tetracritical Phenomena and Scaling Properties of the SO(5) Theory"
The multicritical point at which both a 3-component and a 2-component order
parameters order simultaneously in 3 dimensions is shown to have the critical
behavior of the decoupled fixed point, with separate n=3 and n=2 behavior. This
contradicts both the extrapolation of the epsilon-expansion at leading order,
which yields the biconical point, and recent Monte Carlo simulations, which
gave isotropic SO(5) behavior. Thus, this tetracritical point carries no
information on the relevance of the so-called SO(5) theory of high-T
superconductivity.Comment: 1 pag
Subtleties in QCD theory in Two Dimensions
It is shown that in a formulation of Yang-Mills theory in two dimensions in
terms of A=if^{-1}\pa f, \bar A=i\bar f\bpa\bar f^{-1} with ,
the complexification of , reveals
certain subtleties. ``Physical" massive color singlet states seem to exist.
When coupled to quarks the coupling constant is renormalized in such a
way that it vanishes for the pure Yang- Mills case. This renders the above
states massless and unphysical. In the abelian case, on the other hand, the
known results of the Schwinger model are reproduced with no need of such a
renormalization.
The massless theory is analyzed in similar terms and peculiar massive
states appear, with a mass of .Comment: 21 page
A Note on Softly Broken MQCD
We consider generic MQCD configurations with matter described by semi-infinte
D4-branes and softly broken supersymmetry. We show that the matter sector does
not introduce supersymmetry breaking parameters so that the most relevant
supersymmetry breaking operator at low energies is the gaugino mass term. By
studying the run-away properties of these models in the decoupling limit of the
adjoint matter, we argue that these softly broken MQCD configurations fail to
capture the infrared physics of QCD at scales below the gaugino mass scale.Comment: 10+1 pages, TeX. V2: small comments and acknowledgements added,
conclusions unchange
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