1,721,019 research outputs found
Quantum Weyl invariance and cosmology
No full textAbstractEquations for cosmological evolution are formulated in a Weyl invariant formalism to take into account possible Weyl anomalies. Near two dimensions, the renormalized cosmological term leads to a nonlocal energy-momentum tensor and a slowly decaying vacuum energy. A natural generalization to four dimensions implies a quantum modification of Einstein field equations at long distances. It offers a new perspective on time-dependence of couplings and naturalness with potentially far-reaching consequences for the cosmological constant problem, inflation, and dark energy
Quantum Entanglement in String Theory
No full textWe define entanglement entropy in string perturbation theory using the
orbifold method -- a stringy analog of the replica method in field theory. To
this end, we use the Newton series to analytically continue in the
partition functions for string orbifolds on conical
spaces, known for all odd integer . In the concrete example of
ten-dimensional Type-IIB strings, the one-loop partition function can be
computed explicitly and the one-loop entropy can be expressed as a manifestly
modular invariant series in terms of the Weierstrass function. The
convergence of the series is not evident but, from physical arguments based on
holography, it is expected to yield a finite answer together with the tree
level contribution. This method has a natural generalization to other string
compactifications and to higher genus Riemann surfaces; it can provide a
modular invariant definition of generalized entropy in a given string vacuum to
all orders, of potential interest for the generalized second law of
thermodynamics.Comment: 22 page
Perturbative tests of non-perturbative counting
No full text10 pages, 0 figuresWe observe that a class of quarter-BPS dyons in N=4 theories with charge vector (Q, P) and with nontrivial values of the arithmetic duality invariant I := gcd (Q wedge P) are nonperturbative in one frame but perturbative in another frame. This observation suggests a test of the recently computed nonperturbative partition functions for dyons with nontrivial values of the arithmetic invariant. For all values of I, we show that the nonperturbative counting yields vanishing indexed degeneracy for this class of states everywhere in the moduli space in precise agreement with the perturbative result
Exact counting of supersymmetric black hole microstates
No full textIt is shown that the entropy of certain two-charge supersymmetric black holes in N=4 string theories can be computed to all orders using Wald's formula and the supersymmetric attractor equations with an effective action that includes the relevant higher curvature terms. Classically, these black holes have zero area but the attractor equations are still applicable at the quantum level and result in finite quantum area. The quantum corrected macroscopic entropy agrees precisely with the microscopic counting for an infinite tower of fundamental string states to all orders in an asymptotic expansion
Black hole entropy and attractors
Full text linkThe introductory lectures delivered at the 2006 RTN Winter School on Strings, Supergravity and Gauge Theories at CERN and the 2005 Shanghai Summer School on Recent Trends in M/String Theory were aimed at Ph.D students and recent postdocs. We describe recent progress in understanding quantum aspects of black holes after reviewing the relevant background material, and illustrate the basic concepts with a few examples
Fermions and nonperturbative supersymmetry breaking in the one-dimensional superstring
No full textThe one-dimensional superstring of Marinari and Parisi is analyzed taking into account the fermionic sector. The original matrix model is reduced to a manifestly supersymmetric quantum mechanics of eigenvalues with an effective superpotential. Unlike the bosonic sector, the fermionic sector has long-range interactions between the eigenvalues. It is shown that in the double-scaling limit the dynamics of the top eigenvalue can be described in terms of scaled supercharges. The one-eigenvalue instanton and the corresponding fermionic zero mode responsible for supersymmetry breaking are identified. The supersymmetry breaking parameter is calculated and is shown to be nonzero. The nonperturbative breaking of supersymmetry in this string model goes as exp(-C/χ ), where χ 2 is the loop counting parameter. This is much stronger than the exp(-C/χ 2) nonperturbative effects characteristic of low-energy field theory. Possible implications of this result for critical string theory are discussed
Ramanujan and Quantum Black Holes
No full textExplorations of quantum black holes in string theory have led to fascinating connections with the work of Ramanujan on partitions and mock theta functions, which in turn relate to diverse topics in number theory and enumerative geometry. This article aims to explain the physical significance of these interconnections
Strings2024 Conference
No full textI discuss physical motivations from black hole physics and holography for expecting finite quantum entanglement entropy in quantum gravity. I describe recent and earlier results in defining such a notion in perturbative string theory by a stringy analog of the replica method using ZN orbifolds constructed for any odd positive integer N. The entropy so defined naturally includes a classical piece and is manifestly UV finite but has potential tachyonic IR divergences. I show that for several string compactifications as well as on black hole horizons in AdS3/CFT2 holography, the specific structure of the tachyonic spectrum allows for a re-summation and analytic continuation to the physical region 0 < N ≤ 1 where the IR divergences are absent and the resulting entropy is finite to one-loop order
Strings on a cone and black hole entropy
Full text linkString propagation on a cone with deficit angle 2π (1 - 1/N) is described by constructing a non-compact orbifold of a plane by a ZN subgroup of rotations. It is modular invariant and has tachyons in the twisted sectors that are localized at the tip of the cone. A possible connection with the quantum corrections to the black hole entropy is outlined. The entropy computed by analytically continuing in N would receive contribution only from the twisted sectors and be naturally proportional to the area of the event horizon. Evidence is presented for a new duality for these orbifolds similar to the R →1/R duality
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