151 research outputs found
Coset Models and Differential Geometry
String propagation on a curved background defines an embedding problem of
surfaces in differential geometry. Using this, we show that in a wide class of
backgrounds the classical dynamics of the physical degrees of freedom of the
string involves 2-dim sigma-models corresponding to coset conformal field
theories.Comment: 7 pages, latex;Contribution to the proceedings of the Conference in
Imperial College, London, 5-10 July 1996 and the e--proceedings of the
Conference in Argonne, IL, 27 June - 12 July 199
Branes for Higgs phases and exact conformal field theories
We consider multicenter supergravity solutions corresponding to Higgs phases
of supersymmetric Yang-Mills theories with Z_N symmetric vacua. In certain
energy regimes, we find a description in terms of a generalized wormhole
solution that corresponds to the SL(2,R)/U(1) \times SU(2)/U(1) exact conformal
field theory. We show that U-dualities map these backgrounds to purely
gravitational ones and comment on the relation to the black holes arising from
intersecting D1 and D5 branes. We also discuss supersymmetric properties of the
various solutions and the relation to 2-dim solitons, on flat space, of the
reduced axion-dilaton-gravity equations. Finally, we address the problem of
understanding other supergravity solutions from the multicenter ones. As
prototype examples we use rotating D3 branes and NS5 and D5 branes associated
to non-Abelian duals of 4-dim hyper-Kahler metrics with SO(3) isometry.Comment: 14 pages, latex; v2: a few typos corrected and a reference added.
Version to appear in JHE
Supersymmetric phases of finite-temperature strings II
It was recently proposed that there exist stable supersymmetric phases for
finite temperature superstings. This issue was investigated using an effective
supergravity which takes into account massive winding modes. Such a theory
admits BPS solutions that do not suffer from Hagedorn-type instabilities. We
extend several aspects of this work. First we restrict to the real-field sector
of the theory and allow, in general, for unequal right and left winding fields.
Then, by further specializing to type-II theories (IIA, IIB and a self-dual
hybrid) we construct the most general 1/2-BPS solution and reveal several new
features arising in various consistent truncations. In the heterotic case we
investigate the general properties of the solution which is presented in a
closed form in the limit of infinitely large left-winding field.Comment: 19 pages, latex. v2: clarifying remarks are added and a few typos are
corrected, version to appear in JHE
The black hole and FRW geometries of non-relativistic gravity
We consider the recently proposed non-relativistic Ho\v{r}ava-Lifshitz
four-dimensional theory of gravity. We study a particular limit of the theory
which admits flat Minkowski vacuum and we discuss thoroughly the quadratic
fluctuations around it. We find that there are two propagating polarizations of
the metric. We then explicitly construct a spherically symmetric,
asymptotically flat, black hole solution that represents the analog of the
Schwarzschild solution of GR. We show that this theory has the same Newtonian
and post-Newtonian limits as GR and thus, it passes the classical tests. We
also consider homogeneous and isotropic cosmological solutions and we show that
although the equations are identical with GR cosmology, the couplings are
constrained by the observed primordial abundance of
Non-integrability in non-relativistic theories
Generic non-relativistic theories giving rise to non-integrable string
solutions are classified. Our analysis boils down to a simple algebraic
condition for the scaling parameters of the metric. Particular cases are the
Lifshitz and the anisotropic Lifshitz spacetimes, for which we find that for
trivial dilaton dependence the only integrable physical theory is that for z=1.
For the hyperscaling violation theories we conclude that the vast majority of
theories are non-integrable, while only for a small class of physical theories,
where the Fermi surfaces belong to, integrability is not excluded. Schrodinger
theories are also analyzed and a necessary condition for non-integrability is
found. Our analysis is also applied to cases where the exponential of the
dilaton is a monomial of the holographic coordinate.Comment: 1+20 pages, v2:minor corrections, references adde
Supersymmetric moduli of the SU(2) x R linear dilaton background and NS5-branes
We study several classes of marginal deformations of the conformal field
theory SU(2) x R. This theory describes the near-horizon region of a stack of
parallel and coincident NS5-branes and is related holographically to little
string theory. We investigate the supersymmetry properties of these
deformations and we elucidate their role in the context of holography. The
conformal field theory moduli space contains "non-holographic" operators that
do not seem to have a simple interpretation in little string theory.
Subsequently, we analyze several NS5-brane configurations in terms of SU(2) x R
deformations. We discuss in detail interesting phenomena, like the excision of
the strong coupling region associated with the linear dilaton and the
manifestation of the symmetries of an NS5-brane setup in the deforming
operators. Finally, we present a class of conformally hyperkaehler geometries
that arise as "non-holographic" deformations of SU(2) x R.Comment: 38 pages, 1 figure, 1 table; version to appear in JHE
Gravity duals of N=2 SCFTs and asymptotic emergence of the electrostatic description
We built the first eleven-dimensional supergravity solutions with
SO(2,4)xSO(3)xU(1)_R symmetry that exhibit the asymptotic emergence of an extra
U(1) isometry. This enables us to make the connection with the usual
electrostatics-quiver description. The solution is obtained via the Toda frame
of Kahler surfaces with vanishing scalar curvature and SU(2) action.Comment: 1+15 pages, Latex, v2: few minor changes, JHEP versio
String backgrounds and LCFT
We describe a large class of exact string backgrounds with a null Killing
vector arising, via a limiting \`a la Penrose procedure, from string
backgrounds corresponding to coset conformal field theories for compact groups
G_N/H_N times a free time-like boson U(1)_{-N}. In this way a class of novel
logarithmic conformal field theories (LCFT) emerges, that includes the one
constructed recently as an N\to \infty limit of the SU(2)_N/U(1) X U(1)_{-N}
theory. We explicitly give the exact operator algebra for the basic chiral
fields as well as their representation in terms of free bosons, even though
these are not known in general at finite N. We also compute four-point
functions of various operators in the theory. For the cases of the four- and
five-dimensional models, corresponding to a limit of the theory SO(D+1)_N/SO(D)
X U(1)_{-N} for D=3 and 4, we also present the explicit expressions for the
background fields.Comment: 13 pages, Latex. v2: some refs. added, version to appear in PL
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