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Ioannis Giannakis

Publications and source records attributed to Ioannis Giannakis.

At least 37 records · Page 2Linked to original sources
arXiv2003

Recovery of the Linearized 4D AdS and dS Schwarzschild Metric in the Karch-Randall Braneworld

We present a linearized treatment of the Karch-Randall braneworld where an AdS_4 or dS_4 brane is embedded in AdS_5. We examine the quasi-zero graviton mode in detail and reproduce the graviton mass by elementary means for the AdS_5 case. We also determine the axially symmetric, static excitations of the vacuum and demonstrate that they reproduce the 4D AdS_4 and dS_4 Schwarzschild metrics on the brane.

hep-th↗
arXiv2003

The Ginzburg-Landau Theory and the Surface Energy of a Colour Superconductor

We apply the Ginzburg-Landau theory to the colour superconducting phase of a lump of dense quark matter. We calculate the surface energy of a domain wall separating the normal phase from the super phase with the bulk equilibrium maintained by a critical external magnetic field. Because of the symmetry of the problem, we are able to simplify the Ginzburg-Landau equations and express them in terms of two components of the di-quark condensate and one component of the gauge potential. The equations also contain two dimensionless parameters: the Ginzburg-Landau parameter $κ$ and $ρ$. The main result of this paper is a set of inequalities obeyed by the critical value of the Ginzburg-Landau parameter--the value of $κ$ for which the surface energy changes sign--and its derivative with respect to $ρ$. In addition we prove a number of inequalities of the functional dependence of the surface energy on the parameters of the problem and obtain a numerical solution of the Ginzburg-Landau equations. Finally a criterion for the types of colour superconductivity (type I or type II) is established in the weak coupling approximation.

hep-ph↗
arXiv2002

Linearized Gravity in the Karch-Randall Braneworld

We present a linearized gravity investigation of the bent braneworld, where an AdS_4 brane is embedded in AdS_5. While we focus on static spherically symmetric mass distributions on the brane, much of the analysis continues to hold for more general configurations. In addition to the identification of the massive Karch-Randall graviton and a tower of Kaluza-Klein gravitons, we find a radion mode that couples to the trace of the energy-momentum tensor on the brane. The Karch-Randall radion arises as a property of the embedding of the brane in the bulk space, even in the context of a single brane model.

hep-th↗
arXiv2002

Angular Momentum Mixing in Crystalline Color Superconductivity

In crystalline color superconductivity, quark pairs form at non-zero total momentum. This crystalline order potentially enlarges the domain of color superconductivity in cold dense quark matter. We present a perturbative calculation of the parameters governing the crystalline phase and show that this is indeed the case. Nevertheless, the enhancement is modest, and to lowest order is independent of the strength of the color interaction.

hep-ph↗
arXiv2001

Spacetime Supersymmetry in a nontrivial NS-NS Superstring Background

In this paper we consider superstring propagation in a nontrivial NS-NS background. We deform the world sheet stress tensor and supercurrent with an infinitesimal B_{μν} field. We construct the gauge-covariant super-Poincare generators in this background and show that the B_{μν} field spontaneously breaks spacetime supersymmetry. We find that the gauge-covariant spacetime momenta cease to commute with each other and with the spacetime supercharges. We construct a set of "magnetic" super-Poincare generators that are conserved for constant field strength H_{μνλ}, and show that these generators obey a "magnetic" extension of the ordinary supersymmetry algebra.

hep-th↗
arXiv2001

Linearized Analysis of the Dvali-Gabadadze-Porrati Brane Model

We solve the Einstein equations in the Dvali-Gabadadze-Porrati model with a static, spherically symmetric matter distribution on the physical brane and obtain an exact expression for the gravitational field outside the source to the first order in the gravitational coupling. Although when confined on the physical brane this expression reproduces the correct 4D Newtonian potential for distances r_s << r << λ, where λ is a characteristic length scale of the model, it does not coincide with the standard linearized form of the 4D Schwarzschild metric. The solution reproduces the 5D Schwarzschild metric in the linearized approximation for r >> λ.

hep-th↗
arXiv2001

The Ginzburg-Landau Free Energy Functional of Color Superconductivity at Weak Coupling

We derive the Ginzburg-Landau free energy functional of color superconductivity in terms of the thermal diagrams of QCD in its perturbative region. The zero mode of the quadratic term coefficient yields the same transition temperature, including the pre-exponential factor, as the one obtained previously from the Fredholm determinant of the two quark scattering amplitude. All coefficients of the free energy can be made identical to those of a BCS model by setting the Fermi velocity of the latter equal to the speed of light. We also calculate the induced symmetric color condensate near $T_c$ and find that it scales as the cubic power of the dominant antisymmetric color component. We show that in the presence of an inhomogeneity and a nonzero gauge potential, while the color-flavor locked condensate dominates in the bulk, the unlocked condensate, the octet, emerges as a result of a simultaneous color-flavor rotation in the core region of a vortex filament or at the junction of super and normal phases.

hep-ph↗
arXiv2001

Linearized Gravity in Isotropic Coordinates in the Brane World

We solve the Einstein equations in the Randall-Sundrum framework using an isotropic ansatz for the metric and obtain an exact expression to first order in the gravitational coupling. The solution is free from metric singularities away from the source and it satisfies the Israel matching condition on a straight brane. At distances far away from the source and on the physical brane this solution coincides with the 4-D Schwarzschild metric in isotropic coordinates. Furthermore we show that the extension of the standard Schwarzschild horizon in the bulk is tubular for any diagonal form of the metric while there is no restriction for the extension of the Schwarzschild horizon in isotropic coordinates.

hep-th↗
arXiv2000

Possible Extensions of the 4-d Schwarzschild Horizon in the Brane World

We show that, in the absence of matter in the bulk, the Einstein equations and the Gauss-normal form of the metric place stringent restrictions on the form of the event horizon in a brane world. As a consequence, the off-brane extension of the standard 4-D Schwarzschild horizon in the Randall-Sundrum $AdS_5$ spacetime, as it is viewed from the brane can only be of a tubular shape, instead of a pancake shape. When it is viewed from the $AdS_5$ horizon, such a tubular horizon is absent.

hep-th↗
arXiv2000

Recovery of the Schwarzschild Metric in Theories with Localized Gravity Beyond Linear Order

We solve the Einstein equations in the Randall-Sundrum framework with a static, spherically symmetric matter distribution on the {\it physical brane} and obtain an approximate expression for the gravitational field outside the source to second order in the gravitational coupling. This expression when confined on the {\it physical brane} coincides with the standard form of the Schwarzschild metric. Therefore, the Randall-Sundrum scenario is consistent with the Mercury precession test of General Relativity.

hep-th↗
arXiv1999

Supersymmetry and Gravitational Quadrupoles

We derive model independent, non-perturbative supersymmetric sum rules for the gravitational quadrupole moments of arbitrary-spin particles in any N=1 supersymmetric theory. These sum rules select a ``preferred'' value of h=1 where the ``h-factor'' is the gravitational quadrupole analog of the gyromagnetic ratio or g-factor. This value of h=1 corresponds identically to the preferred field theory value obtained by tree-level unitarity considerations. The presently derived h-factor sum rule complements and generalizes previous work on electromagnetic moments where g=2 was shown to be preferred by both supersymmetric sum rule and tree-level unitarity arguments.

hep-th↗
arXiv1999

Superconformal Deformations and Space-Time Symmetries

In this paper we present a method of deforming to first order the stress-tensor and the supercurrent of the superstring corresponding to turning on NS-NS bosonic fields. Furthermore we discuss the difficulties associated with turning on spacetime fermions and R-R bosons. We also derive the gauge symmetries of the massless spacetime fields.

hep-th↗
arXiv1998

Anisotropic Null String Cosmologies

We study string propagation in an anisotropic, cosmological background. We solve the equations of motion and the constraints by performing a perturbative expansion of the string coordinates in powers of c^2, the world-sheet speed of light. To zeroth order the string is approximated by a tensionless string (since c is proportional to the string tension T). We obtain exact, analytical expressions for the zeroth and the first order solutions and we discuss some cosmological implications.

gr-qc↗
arXiv1998

Massive Higher Spin States in String Theory and the Principle of Equivalence

In this paper we study three point functions of the Type II superstring involving one graviton and two massive states, focusing in particular on the spin-7/2 fermions at the first mass level. Defining a gravitational quadrupole ``h-factor'', we find that the non-minimal interactions of string states in general are parametrized by $h\ne1$, in contrast to the preferred field theory value of h=1 (for tree-level unitarity). This difference arises from the fact that consistent gravitational interactions of strings are related to the presence of a complete tower of massive states, not present in the ordinary field theory case.

hep-th↗
arXiv1998

Supersymmetric Sum Rules for Electromagnetic Multipoles

We derive model independent, non-perturbative supersymmetric sum rules for the magnetic and electric multipole moments of any theory with N=1 supersymmetry. We find that in any irreducible N=1 supermultiplet the diagonal matrix elements of the l-multipole moments are completely fixed in terms of their off-diagonal matrix elements and the diagonal (l-1)-multipole moments.

hep-th↗
arXiv1997

N=2 Supersymmetry and Dipole Moments

We derive sum rules for the magnetic and electric dipole moments of all particle states of an N=2 supermultiplet. For short representations, we find agreement with previously determined N=1 sum rules, while there is added freedom for long representations (expressed as certain scalar expectation values). With mild assumptions we find the simple result that the supersymmetry generated spin adds to the magnetic (electric) dipole moment with strength corresponding to $g=2$ ($g_e=0$). This result is equally valid for N=1, this time without any further assumptions.

hep-th↗
arXiv1997

Higgs Mechanism in String Theory

In first-quantized string theory, spacetime symmetries are described by inner automorphisms of the underlying conformal field theory. In this paper we use this approach to illustrate the Higgs effect in string theory. We consider string propagation on M^{24,1} \times S^1, where the circle has radius R, and study SU(2) symmetry breaking as R moves away from its critical value. We find a gauge-covariant equation of motion for the broken-symmetry gauge bosons and the would-be Goldstone bosons. We show that the Goldstone bosons can be eliminated by an appropriate gauge transformation. In this unitary gauge, the Goldstone bosons become the longitudinal components of massive gauge bosons.

hep-th↗