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A. Giveon

Publications and source records attributed to A. Giveon.

At least 19 recordsLinked to original sources
arXiv2006

Multitrace Deformations of Vector and Adjoint Theories and their Holographic Duals

We present general methods to study the effect of multitrace deformations in conformal theories admitting holographic duals in Anti de Sitter space. In particular, we analyse the case that these deformations introduce an instability both in the bulk AdS space and in the boundary CFT. We also argue that multitrace deformations of the O(N) linear sigma model in three dimensions correspond to nontrivial time-dependent backgrounds in certain theories of infinitely many interacting massless fields on AdS_4, proposed years ago by Fradkin and Vasiliev. We point out that the phase diagram of a truly marginal large-N deformation has an infrared limit in which only an O(N) singlet field survives. We draw from this case lessons on the full string-theoretical interpretation of instabilities of the dual boundary theory and exhibit a toy model that resolves the instability of the O(N) model, generated by a marginal multitrace deformation. The resolution suggests that the instability may not survive in an appropriate UV completion of the CFT.

hep-th↗
arXiv2005

The Charged Black Hole/String Transition

We generalize the discussion of hep-th/0509170 to charged black holes. For the two dimensional charged black hole, which is described by an exactly solvable worldsheet theory, a transition from the black hole to the string phase occurs when the Hawking temperature of the black hole reaches a limiting value, the temperature of free strings with the same mass and charge. At this point a tachyon winding around Euclidean time in the Euclidean black hole geometry, which has a non-zero condensate, becomes massless at infinity, and the horizon of the black hole is infinitely smeared. For Reissner-Nordstrom black holes in d\ge 4 dimensions, the exact worldsheet CFT is not known, but we propose that it has similar properties. We check that the leading order solution is in good agreement with this proposal, and discuss the expected form of α' corrections.

hep-th↗
arXiv2005

Phases of Quantum Gravity in AdS3 and Linear Dilaton Backgrounds

We show that string theory in AdS3 has two distinct phases depending on the radius of curvature R_{AdS}=\sqrt{k}l_s. For k>1 (i.e. R_{AdS}>l_s), the SL(2,C) invariant vacuum of the spacetime conformal field theory is normalizable, the high energy density of states is given by the Cardy formula with c_{eff}=c, and generic high energy states look like large BTZ black holes. For k<1, the SL(2,C) invariant vacuum as well as BTZ black holes are non-normalizable, c_{eff} \half). The states responsible for this growth are two dimensional black holes for k>1, and highly excited perturbative strings living in the linear dilaton throat for k<1. The change of behavior at k=1 in the two cases is an example of a string/black hole transition. The entropies of black holes and strings coincide at k=1.

hep-th↗
arXiv2004

On Thermodynamical Properties of Some Coset CFT Backgrounds

We investigate the thermodynamical features of two Lorentzian signature backgrounds that arise in string theory as exact CFTs and possess more than two disconnected asymptotic regions: the 2-d charged black hole and the Nappi-Witten cosmological model. We find multiple smooth disconnected Euclidean versions of the charged black hole background. They are characterized by different temperatures and electro-chemical potentials. We show that there is no straightforward analog of the Hartle-Hawking state that would express these thermodynamical features. We also obtain multiple Euclidean versions of the Nappi-Witten cosmological model and study their singularity structure. It suggests to associate a non-isotropic temperature with this background.

hep-th↗
arXiv2002

From Big Bang to Big Crunch and Beyond

We study a quotient Conformal Field Theory, which describes a 3+1 dimensional cosmological spacetime. Part of this spacetime is the Nappi-Witten (NW) universe, which starts at a ``big bang'' singularity, expands and then contracts to a ``big crunch'' singularity at a finite time. The gauged WZW model contains a number of copies of the NW spacetime, with each copy connected to the preceeding one and to the next one at the respective big bang/big crunch singularities. The sequence of NW spacetimes is further connected at the singularities to a series of non-compact static regions with closed timelike curves. These regions contain boundaries, on which the observables of the theory live. This suggests a holographic interpretation of the physics.

hep-th↗
arXiv2002

Geometric Transitions, Brane Dynamics and Gauge Theories

We consider the interplay between brane constructions and type IIA, IIB or M-theory geometries on Calabi-Yau (CY) and G_2 holonomy manifolds. This is related to N=1 (and N=2) gauge theories in four dimensions. We first discuss simple geometric transitions corresponding to brane set ups involving orthogonal (or parallel) Neveu-Schwarz branes that approach each other. This is related to confinement and Seiberg duality in SQCD. In particular, we argue that in type IIA, a CP^1 of singularities and one unit of Ramond-Ramond (RR) flux is dual to a D6 brane wrapped on a Lens space, describing the UV and IR of N=1 Super-Yang-Mills (SYM), respectively. Also, in the large N_c duality that relates D6 branes on S^3 to an S^2 with RR flux, we implement the presence of $N_f$ flavors of quarks. We then compactify M-theory on T^*(S^3) X S^1)/Z_2 and observe that one phase describes SO(4) SYM in the UV and two others describe confinement. Moreover, we consider compact 7-spaces (CY X S^1)/Z_2. We describe transitions where disconnected S^3's approach and connect each other before they vanish. These effects correspond to non-Abelian Higgs mechanism and confinement. The similar transitions involving S^2 X S^1's are also considered. Finally, we present transitions at finite distance in moduli space, where the first Betti number b_1 of 3-cycles of singularities changes.

hep-th↗
arXiv2001

Comments on D-branes in AdS_3

We study D-branes that preserve a diagonal SL(2) affine Lie algebra in string theory on AdS_3. We find three classes of solutions, corresponding to the following representations of SL(2): (1) degenerate, finite dimensional representations with half integer spin, (2) principal continuous series, (3) principal discrete series. We solve the bootstrap equations for the vacuum wave functions and discuss the corresponding open string spectrum. We argue that from the point of view of the AdS/CFT correspondence, the above D-branes introduce boundaries with conformal boundary conditions into the two dimensional spacetime. Open string vertex operators correspond to boundary perturbations. We also comment on the geometric interpretation of the branes.

hep-th↗
arXiv2001

Notes on AdS_3

We use the conjectured strong-weak coupling worldsheet duality between the SL(2)/U(1) and Sine-Liouville conformal field theories to study some properties of degenerate operators and to compute correlation functions in CFT on AdS_3. The same quantities have been computed in the past by other means. The agreement between the different approaches provides new evidence for the duality. We also discuss the supersymmetric analog of this duality, the correspondence between SCFT on the cigar and N=2 Liouville. We show that in the spacetime CFT dual to string theory on AdS_3 via the AdS/CFT correspondence, the central term in the Virasoro algebra takes different values in different sectors of the theory. In a companion paper we use the results described here to study D-branes in AdS_3.

hep-th↗
arXiv1999

Little String Theory in a Double Scaling Limit

A double scaling limit can be defined in string theory on a Calabi-Yau (CY) manifold by approaching a point in moduli space where the CY space develops an isolated singularity and at the same time taking the string coupling to zero, while keeping a particular combination of the two parameters fixed. This leads to a decoupled theory without gravity which has a weak coupling expansion, and can be studied using a holographically dual non-critical superstring description. The usual ``Little String Theory'' corresponds to the strong coupling limit of this theory. We use holography to compute two and three point functions in weakly coupled double scaled little string theory, and study the spectrum of the theory in various dimensions. We find a discrete spectrum of masses which exhibits Hagedorn growth.

hep-th↗
arXiv1999

Holography for Non-Critical Superstrings

We argue that a class of ``non-critical superstring'' vacua is holographically related to the (non-gravitational) theory obtained by studying string theory on a singular Calabi-Yau manifold in the decoupling limit $g_s\to 0$. In two dimensions, adding fundamental strings at the singularity of the CY manifold leads to conformal field theories dual to a recently constructed class of $AdS_3$ vacua. In four dimensions, special cases of the construction correspond to the theory on an NS5-brane wrapped around a Riemann surface.

hep-th↗
arXiv1998

Brane Dynamics and Gauge Theory

We review some aspects of the interplay between the dynamics of branes in string theory and the classical and quantum physics of gauge theories with different numbers of supersymmetries in various dimensions.

hep-th↗
arXiv1998

Comments on String Theory on $AdS_3$

We study string propagation on $AdS_3$ times a compact space from an ``old fashioned'' worldsheet point of view of perturbative string theory. We derive the spacetime CFT and its Virasoro and current algebras, thus establishing the conjectured $AdS$/CFT correspondence for this case in the full string theory. Our results have implications for the extreme IR limit of the $D1-D5$ system, as well as to 2+1 dimensional BTZ black holes and their Bekenstein-Hawking entropy.

hep-th↗
arXiv1998

Algebraic Aspects of Matrix Theory on T^d

We study the exceptional U duality group $E_d$ of M-theory compactified on a d-torus and its representations using Matrix theory. We exhibit the $E_d$ structure and show that p-branes wrapped or unwrapped around the longitudinal direction form representations of the U duality group together with other, more mysterious, states.

hep-th↗
arXiv1997

Brane Dynamics and N=1 Supersymmetric Gauge Theory

We discuss some aspects of the relation between space-time properties of branes in string theory, and the gauge theory on their worldvolume, for models invariant under four supercharges in three and four dimensions. We show that a simple set of rules governing brane dynamics reproduces many features of gauge theory. We study theories with $U(N_c)$, $SO(N_c)$ and $Sp(N_c)$ gauge groups and matter in the fundamental and two index tensor representations, and use the brane description to establish Seiberg's electric-magnetic duality for these models.

hep-th↗
arXiv1996

Aspects of Space-Time Dualities

Duality groups of Abelian gauge theories on four manifolds and their reduction to two dimensions are considered. The duality groups include elements that relate different space-times in addition to relating different gauge-coupling matrices. We interpret (some of) such dualities as the geometrical symmetries of compactified theories in higher dimensions. In particular, we consider compactifications of a (self-dual) 2-form in 6-D, and compactifications of a self-dual 4-form in 10-D. Relations with a self-dual superstring in 6-D and with the type IIB superstring are discussed.

hep-th↗