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F. Loran

Publications and source records attributed to F. Loran.

18 recordsLinked to original sources
arXiv2016

Non-chiral 2d CFT with integer energy levels

The partition function of 2d conformal field theory is a modular invariant function. It is known that the partition function of a holomorphic CFT whose central charge is a multiple of 24 is a polynomial in the Klein function. In this paper, by using the medium temperature expansion we show that every modular invariant partition function can be mapped to a holomorphic partition function whose structure can be determined similarly. We use this map to study partition function of CFTs with half-integer left and right conformal weights. We show that the corresponding left and right central charges are necessarily multiples of 4. Furthermore, the degree of degeneracy of high-energy levels can be uniquely determined in terms of the degeneracy in the low energy states.

hep-th↗
arXiv2012

Gravity/CFT correspondence for three dimensional Einstein gravity with a conformal scalar field

We study the three dimensional Einstein gravity conformally coupled to a scalar field. Solutions of this theory are geometries with vanishing scalar curvature. We consider solutions with a constant scalar field which corresponds to an infinite Newton's constant. There is a class of solutions with possible curvature singularities which asymptotic symmetries are given by two copies of the Virasoro algebra. We argue that the central charge of the corresponding CFT is infinite. Furthermore, we construct a family of Schwarzschild solutions which can be conformally mapped to the Martinez-Zanelli solution of Einstein's equations with a negative cosmological constant coupled to conformal scalar field.

hep-th↗
arXiv2011

Beyond Logarithmic Corrections to Cardy Formula

As shown by Cardy modular invariance of the partition function of a given unitary non-singular 2d CFT with left and right central charges c_L and c_R, implies that the density of states in a microcanonical ensemble, at excitations Delta and Delta-bar and in the saddle point approximation, is ρ_0(Δ,\barΔ;c_L, c_R)=c_L c_R \exp(2π\sqrt{{c_LΔ}/{6}})\exp(2π\sqrt{{c_R\barΔ}/{6}}). In this paper, we extend Cardy's analysis and show that in the saddle point approximation and up to contributions which are exponentially suppressed compared to the leading Cardy's result, the density of states takes the form ρ(Δ,\barΔ; c_L,c_R)= f(c_LΔ) f(c_R\barΔ)ρ_0(Δ,\barΔ; c_L, c_R), for a function f(x) which we specify. In particular, we show that (i) ρ(Δ,\barΔ; c_L, c_R) is the product of contributions of left and right movers and hence, to this approximation, the partition function of any modular invariant, non-singular unitary 2d CFT is holomorphically factorizable and (ii) ρ(Δ,\barΔ; c_L, c_R)/(c_Lc_R) is only a function of $c_R\barΔ$ and $c_LΔ$. In addition, treating ρ(Δ,\barΔ; c_L, c_R) as the density of states of a microcanonical ensemble, we compute the entropy of the system in the canonical counterpart and show that the function f(x) is such that the canonical entropy, up to exponentially suppressed contributions, is simply given by the Cardy's result \lnρ_0(Δ,\barΔ; c_L, c_R).

hep-th↗
arXiv2010

Orientifolded Locally AdS3 Geometries

Continuing the analysis of [arXiv:1003.4089[hep-th]], we classify all locally AdS3 stationary axi-symmetric unorientable solutions to AdS3 Einstein gravity and show that they are obtained by applying certain orientifold projection on AdS3, BTZ or AdS3 self-dual orbifold, respectively O-AdS3, O-BTZ and O-SDO geometries. Depending on the orientifold fixed surface, the O-surface, which is either a space-like 2D plane or cylinder, or a light-like 2D plane or cylinder one can distinguish four distinct cases. For the space-like orientifold plane or cylinder cases these geometries solve AdS3 Einstein equations and are hence locally AdS3 everywhere except at the O-surface, where there is a delta-function source. For the light-like cases the geometry is a solution to Einstein equations even at the O-surface. We discuss the causal structure for static, extremal and general rotating O-BTZ and O-SDO cases as well as the geodesic motion on these geometries. We also discuss orientifolding Poincare patch AdS3 and AdS2 geometries as a way to geodesic completion of these spaces and comment on the 2D CFT dual to the O-geometries.

hep-th↗
arXiv2010

O-BTZ: Orientifolded BTZ Black Hole

Banados-Teitelboim-Zanelli (BTZ) black holes are constructed by orbifolding AdS3 geometry by boost transformations of its O(2,2) isometry group. Here we construct a new class of solutions to AdS3 Einstein gravity, orientifolded BTZ or O-BTZ for short, which in general, besides the usual BTZ orbifolding, involve orbifolding (orientifolding) by a Z_2 part of O(2,2) isometry group. This Z_2 is chosen such that it changes the orientation on AdS3 while keeping the orientation on its 2D conformal boundary. O-BTZ solutions exhaust all un-oriented AdS3 black hole solutions, as BTZ black holes constitute all oriented AdS3 black holes. O-BTZ, similarly to BTZ black holes, are stationary, axisymmetric asymptotically AdS3 geometries with two asymptotic charges, mass and angular momentum..

hep-th↗
arXiv2009

5D Extremal Rotating Black Holes and CFT duals

Kerr/CFT correspondence has been recently applied to various types of 5D extremal rotating black holes. A common feature of all such examples is the existence of two chiral CFT duals corresponding to the U(1) symmetries of the near horizon geometry. In this paper, by studying the moduli space of the near horizon metric of five dimensional extremal black holes which are asymptotically flat or AdS, we realize an SL(2,Z) modular group which is a symmetry of the near horizon geometry. We show that there is a lattice of chiral CFT duals corresponding to the moduli points identified under the action of the modular group. The microscopic entropy corresponding to all such CFTs are equivalent and are in agreement with the Bekenstein-Hawking entropy.

hep-th↗
arXiv2009

Near the horizon of 5D black rings

For the five dimensional N=2 black rings, we study the supersymmetry enhancement and identify the global supergroup of the near horizon geometry. We show that the global part of the supergroup is OSp(4*|2)X U(1) which is similar to the small black string. We show that results obtained by applying the entropy function formalism, the c-extremization approach and the Brown-Henneaux method to the black ring solution are in agreement with the microscopic entropy calculation.

hep-th↗
arXiv2006

Bound State of an Electron on a $^4$He Superfluid Droplet as a Test for Quantum Gravity

We address the problem of finding a system in which there would be measurable quantum gravitational effects. Following standard quantum-field methods, we have calculated the first-order radiative correction of graviton exchange on the binding energy of an electron with an ultra cold superfluid droplet of $^4$He with mass about the Planck mass. For two $^4$He droplets with a mass difference of about one microgram, we show that the relative difference in the binding energies is about one percent.

gr-qc↗
arXiv2005

Metastable de Sitter vacua from critical scalar theory

Studying the critical scalar theory in four dimensional Euclidean space with the potential term $-g\phi^4$ we show that the theory can not be analytically continued through g=0 from g<0 region to g>0 region. For g>0 although energy is not bounded from below but there exist a classical trajectory with an AdS5 moduli space, corresponding to a metastable local minima of the action. The fluctuation around this solution is governed by a minimally coupled scalar theory on four dimensional de Sitter background with a reversed Mexican hat potential. Since in the weak coupling limit, the partition function picks up contribution only around classical solutions, one can assume that our de Sitter universe corresponds to that local minima which lifetime increases exponentially as the coupling constant tends to zero. Similar results is obtained in the case of critical scalar theory coupled to U(1) gauge field which is essential for people living on flat Euclidean space to observe a de Sitter background by optical instruments.

hep-th↗
arXiv2003

Three Body Bound State in Non-Commutative Space

The Bethe-Salpeter equation in non-commutative QED (NCQED) is considered for three-body bound state. We study the non-relativistic limit of this equation in the instantaneous approximation and derive the corresponding Schrödinger equation in non-commutative space. It is shown that the experimental data for Helium atom puts an upper bound on the magnitude of the parameter of non-commutativity, $θ\sim10^{-9}λ_e^2$.

hep-th↗
arXiv2002

Abelian Subset of Second Class Constraints

We show that after mapping each element of a set of second class constraints to the surface of the other ones, half of them form a subset of abelian first class constraints. The explicit form of the map is obtained considering the most general Poisson structure. We also introduce a proper redefinition of second class constraints that makes their algebra symplectic.

hep-th↗
arXiv2002

Abelianization of First Class Constraints

We show that a given set of first class constraints becomes abelian if one maps each constraint to the surface of other constraints. There is no assumption that first class constraints satisfy a closed algebra. The explicit form of the projection map is obtained at least for irreducible first class constraints. Using this map we give a method to obtain gauge fixing conditions such that the set of abelian first class constraints and gauge fixing conditions satisfy the symplectic algebra.

hep-th↗
arXiv2002

Comment on "Constraint Quantization of Open String in Background B field and Noncommutative D-brane"

In the paper "Constraint Quantization of Open String in Background $B$ field and Noncommutative D-brane", it is claimed that the boundary conditions lead to an infinite set of secondary constraints and Dirac brackets result in a non-commutative Poisson structure for D-brain. Here we show that contrary to the arguments in that paper, the set of secondary constraints on the boundary is finite and the non-commutativity algebra can not be obtained by evaluating the Dirac brackets.

hep-th↗
arXiv2002

Positronium Hyperfine Splitting in Non-commutative Space at the Order $α^6$

We obtain positronium Hyperfine Splitting owing to the non-commutativity of space and show that, in the leading order, it is proportional to $θα^6$ where, $θ$ is the parameter of non-commutativity. It is also shown that spatial non-commutativity splits the spacing between $n=2$ triplet excited levels $E(2^3S_1)\to E(2^3P_2)$ which provides an experimental test on the non-commutativity of space.

hep-ph↗
arXiv2002

A Dynamical Approach to Gauge Fixing

We study gauge fixing in the generalized Gupta-Bleuler quantization. In this method physical states are defined to be simultaneous null eigenstates of a set of quantum invariants. We apply the method to a solvable model proposed by Friedberg, Lee, Pang and Ren and show that no Gribov-type copies appears by construction.

hep-th↗
arXiv2002

On The Quantization Of Constraint Systems: A Lagrangian Approach

It is possible to introduce external time dependent back ground fields in the formulation of a system as fields whose dynamics can not be deduced from Euler Lagrange equations of motion. This method leads to singular Lagrangians for real systems. We discuss quantization of constraint systems in these cases and introduce generalized Gupta-Bleuler quantization. In two examples we show explicitly that this method of quantization leads to true Schrödinger equations.

hep-th↗
arXiv2001

Scalar-Scalar Bound State in Non-commutative Space

Bethe-Salpeter equation in the non-commutative space for a scalar-scalar bound state is considered. It is shown that in the non-relativistic limit, the effect of spatial non-commutativity appears as if there exist a magnetic dipole moment coupled to each particle.

hep-th↗