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Shmuel Elitzur

Publications and source records attributed to Shmuel Elitzur.

16 recordsLinked to original sources
arXiv2013

On periodically driven AdS/CFT

We use the AdS/CFT correspondence to study a thermally isolated conformal field theory in four dimensions which undergoes a repeated deformation by an external periodic time-dependent source coupled to an operator of dimension Delta. The initial state of the theory is taken to be at a finite temperature. We compute the energy dissipated in the system as a function of the frequency and of the dimension Delta of the perturbing operator. This is done in the linear response regime. In order to study the details of thermalization in the dual field theory, the leading-order backreaction on the AdS black brane metric is computed. The evolution of the event and the apparent horizons is monitored; the increase of area in each cycle coincides with the increase in the equilibrium entropy corresponding to the amount of energy dissipated. The time evolution of the entanglement entropy of a spherical region and that of the two-points function of a probe operator with a large dimension are also inspected; we find a delay in the thermalization of these quantities which is proportional to the size of the region which is being probed. Thus, the delay is more pronounced in the infrared. We comment on a possible transition in the time evolution of the energy fluctuations.

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arXiv2013

Defects, Super-Poincaré line bundle and Fermionic T-duality

Topological defects are interfaces joining two conformal field theories, for which the energy momentum tensor is continuous across the interface. A class of the topological defects is provided by the interfaces separating two bulk systems each described by its own Lagrangian, where the two descriptions are related by a discrete symmetry. In this paper we elaborate on the cases in which the discrete symmetry is a bosonic or a fermionic T- duality. We review how the equations of motion imposed by the defect encode the general bosonic T- duality transformations for toroidal compactifications. We generalize this analysis in some detail to the case of topological defects allowed in coset CFTs, in particular to those cosets where the gauged group is either an axial or vector U(1). This is discussed in both the operator and Lagrangian approaches. We proceed to construct a defect encoding a fermionic T-duality. We show that the fermionic T-duality is implemented by the Super-Poincaré line bundle. The observation that the exponent of the gauge invariant flux on a defect is a kernel of the Fourier-Mukai transform of the Ramond-Ramond fields, is generalized to a fermionic T-duality. This is done via a fiberwise integration on supermanifolds.

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arXiv2012

Induced Boundary Flow on the c = 1 Orbifold Moduli Space

Boundary flow in the $c=1$ 2d CFT of a $\mathbb{Z}_2$ orbifold of a free boson on a circle is considered. Adding a bulk marginal operator to the $c=1$ orbifold branch induces a boundary flow. We show that this flow is consistent for any bulk marginal operator and known initial given boundary condition. The supersymmetric $c=3/2$ case is also mentioned. The supersymmetric $c=3/2$ case is also mentioned. For the circle branch of the moduli space this has been shown in arXiv:hep-th/0609034v2. The ground state multiplicity ($g_b$) is calculated and it is shown that it does indeed decrease.

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arXiv2012

Time-dependent stabilization in AdS/CFT

We consider theories with time-dependent Hamiltonians which alternate between being bounded and unbounded from below. For appropriate frequencies dynamical stabilization can occur rendering the effective potential of the system stable. We first study a free field theory on a torus with a time-dependent mass term, finding that the stability regions are described in terms of the phase diagram of the Mathieu equation. Using number theory we have found a compactification scheme such as to avoid resonances for all momentum modes in the theory. We further consider the gravity dual of a conformal field theory on a sphere in three spacetime dimensions, deformed by a doubletrace operator. The gravity dual of the theory with a constant unbounded potential develops big crunch singularities; we study when such singularities can be cured by dynamical stabilization. We numerically solve the Einstein-scalar equations of motion in the case of a time-dependent doubletrace deformation and find that for sufficiently high frequencies the theory is dynamically stabilized and big crunches get screened by black hole horizons.

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arXiv2011

Open/Closed Topological CP1 Sigma Model Revisited

We consider the topological sigma-model on Riemann surfaces with genus g and h holes, and target space CP1. We calculate the correlation functions of bulk and boundary operators, and study the symmetries of the model and its most general deformation. We study the open/closed topological field theory (TFT) correspondence by summing up the boundaries. We argue that this summation can be understood as a renormalization of the closed TFT. We couple the model to topological gravity and derive constitutive relations between the correlation functions of bulk and boundary operators.

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arXiv2011

Vacuum stability, string density of states and the Riemann zeta function

We study the distribution of graded degrees of freedom in classically stable oriented closed string vacua and use the Rankin-Selberg transform to link it to the finite one-loop vacuum energy. In particular, we find that the spectrum of physical excitations not only must enjoy asymptotic supersymmetry but actually, at very large mass, bosonic and fermionic states must follow a universal oscillating pattern, whose frequencies are related to the zeros of the Riemann zeta-function. Moreover, the convergence rate of the overall number of the graded degrees of freedom to the value of the vacuum energy is determined by the Riemann hypothesis. We discuss also attempts to obtain constraints in the case of tachyon-free open-string theories.

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arXiv2010

On Uplifted SUSY-Breaking Vacua and Direct Mediation in Generalized SQCD

We search for viable models of direct gauge mediation, where the SUSY-breaking sector is (generalized) SQCD, which has cosmologically favorable uplifted vacua even when the reheating temperature is well above the messenger scale. This requires a relatively large tadpole term in the scalar potential for the spurion field X and, consequently, we argue that pure (deformed) SQCD is not a viable model. On the other hand, in SQCD with an adjoint, which is natural e.g. in string theory, assuming an appropriate sign in the Kahler potential for X, such metastable vacua are possible.

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arXiv2003

Probing Orientifold Behavior Near NS Branes

The effect of NS 5 branes on an orientifold is studied. The orientifold is allowed to pass through a pile of k NS branes forming a regularized CHS geometry. Its effect on open strings in its vicinity is used to study the change in the orientifold charge induced by the NS branes.

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arXiv2002

Removing Singularities

Big bang/crunch curvature singularities in exact CFT string backgrounds can be removed by turning on gauge fields. This is described within a family of {SL(2)xSU(2)xU(1)_x}/{U(1)xU(1)} quotient CFTs. Uncharged incoming wavefunctions from the ``whiskers'' of the extended universe can be fully reflected if and only if a big bang/crunch curvature singularity, from which they are scattered, exists. Extended BTZ-like singularities remain as long as U(1)_x is compact.

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arXiv2001

D-Branes on a gauged WZW model

The algebraic classification of Cardy for boundary states on a $G/H$ coset CFT of a compact group G, is geometrically realized on the corresponding manifold resulting from gauging the WZW model. The branes consist of H orbits of quantized G conjugacy classes shifted by quantized H conjugacy classes.

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arXiv2000

D-Branes in the Background of NS Fivebranes

We study the dynamics of $D$-branes in the near-horizon geometry of $NS$ fivebranes. This leads to a holographically dual description of the physics of $D$-branes ending on and/or intersecting $NS5$-branes. We use it to verify some properties of such $D$-branes which were deduced indirectly in the past, and discuss some instabilities of non-supersymmetric brane configurations. Our construction also describes vacua of Little String Theory which are dual to open plus closed string theory in asymptotically linear dilaton spacetimes.

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arXiv1999

On Least Action D-Branes

We discuss the effect of relevant boundary terms on the nature of branes. This is done for toroidal and orbifold compactifications of the bosonic string. Using the relative minimalization of the boundary entropy as a guiding principle, we uncover the more stable boundary conditions at different regions of moduli space. In some cases, Neumann boundary conditions dominate for small radii while Dirichlet boundary conditions dominate for large radii. The c=1 and c=2 moduli spaces are studied in some detail. The antisymmetric background field B is found to have a more limited role in the case of Dirichlet boundary conditions. This is due to some topological considerations. The results are subjected to T-duality tests and the special role of the points in moduli space fixed under T-duality is explained from least-action considerations.

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arXiv1998

String Theory on AdS_3 x S^3 x S^3 x S^1

Spacetime properties of superstrings on AdS_3 x S^3 x S^3 x S^1 are studied. The boundary theory is a two dimensional superconformal field theory with a large N=(4,4) supersymmetry.

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arXiv1998

Aspects of Confinement and Screening in M theory

Confinement and Screening are investigated in SUSY gauge theories, realized by an M5 brane configuration, extending an approach applied previously to N=1 SYM theory, to other models. The electric flux tubes are identified as M2 branes ending on the M5 branes and the conserved charge they carry is identified as a topological property. The group of charges carried by the flux tubes is calculated and the results agree in all cases considered with the field theoretical expectations. In particular, whenever the dynamical matter is expected to screen the confining force, this is reproduced correctly in the M theory realization.

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arXiv1998

Branes, Orientifolds and Chiral Gauge Theories

We discuss some aspects of the physics of branes in the presence of orientifolds and the corresponding worldvolume gauge dynamics. We show that at strong coupling orientifolds sometimes turn into bound states of orientifolds and branes, and give a worldsheet argument for the flip of the sign of an orientifold plane split into two disconnected parts by an NS fivebrane. We also describe the moduli space of vacua of N=2 supersymmetric gauge theories with symplectic and orthogonal gauge groups, and analyze a set of four dimensional N=1 supersymmetric gauge theories with chiral matter content using branes.

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