arXiv subjects

Costas Kounnas

Publications and source records attributed to Costas Kounnas.

64 records · Page 4Linked to original sources

arXiv1996

Large Softly broken N=2 QCD

We analyze the possible soft breaking of $N=2$ supersymmetric Yang-Mills theory with and without matter flavour preserving the analyticity properties of the Seiberg-Witten solution. For small supersymmetry breaking parameter with respect to the dynamical scale of the theory we obtain an exact expression for the effective potential. We describe in detail the onset of the confinement transition and some of the patterns of chiral symmetry breaking. If we extrapolate the results to the limit where supersymmetry decouples, we obtain hints indicating that perhaps a description of the QCD vacuum will require the use of Lagrangians containing simultaneously mutually non-local degrees of freedom (monopoles and dyons).

hep-th↗

arXiv1995

Superstring Extension of the Standard Model and Gravitation

Some of the four-dimensional Superstring solutions provide a consistent framework for a Supersymmetric Unification of all interactions including gravity. A class of them extends successfully the validity of the standard model up to the string scale ${\cal O}(10^{17})~GeV$. We stress the importance of string corrections which are relevant for low energy ${\cal O}(1)~TeV$ predictions of gauge and Yukawa couplings as well as the spectrum of the supersymmetric particles after supersymmetry breaking.

hep-th↗

arXiv1995

Infrared behavior of Closed Superstrings in Strong Magnetic and Gravitational Fields

A large class of four-dimensional supersymmetric ground states of closed superstrings with a non-zero mass gap are constructed. For such ground states we turn on chromo-magnetic fields as well as curvature. The exact spectrum as function of the chromo-magnetic fields and curvature is derived. We examine the behavior of the spectrum, and find that there is a maximal value for the magnetic field $H_{\rm max}\sim M_{\rm planck}^2$. At this value all states that couple to the magnetic field become infinitely massive and decouple. We also find tachyonic instabilities for strong background fields of the order ${\cal O}(μM_{\rm planck})$ where $μ$ is the mass gap of the theory. Unlike the field theory case, we find that such ground states become stable again for magnetic fields of the order ${\cal O}(M^2_{\rm planck})$. The implications of these results are discussed.

hep-th↗

arXiv1995

String Gravity and Cosmology: Some new ideas

String theory provides the only consistent framework so far that unifies all interactions including gravity. We discuss gravity and cosmology in string theory. Conventional notions from general relativity like geometry, topology etc. are well defined only as low energy approximations in string theory. At small distances physics deviates from the field theoretic intuition. We present several examples of purely stringy phenomena which imply that the physics at strong curvatures can be quite different from what one might expect from field theory. They indicate new possibilities in the context of quantum cosmology.

gr-qc↗

arXiv1995

Instabilities in Strong Magnetic Fields in String Theory

We construct groundstates of the string with non-zero mass gap and non-trivial chromo-magnetic fields as well as curvature. The exact spectrum as function of the chromo-magnetic fields and curvature is derived. We examine the behavior of the spectrum, and find that there is a maximal value for the magnetic field $H_{\rm max}\sim M_{\rm Plank}^2$. At this value all states that couple to the magnetic field become infinitely massive and decouple. We also find tachyonic instabilities for strong background fields of the order ${\cal O}(μM_{\rm Plank})$ where $μ$ is the mass gap of the theory. Unlike the field theory case, we find that such ground states become stable again for magnetic fields of the order ${\cal O}(M^2_{\rm Plank})$. The implications of these results are discussed.

hep-th↗

arXiv1995

One Loop Corrections to Coupling Constants in IR-regulated String Theory

Exact Superstring solutions are constructed moving in 4-D space-time with positive curvature and non-trivial dilaton and antisymmetric tensor fields. The full spectrum of string excitations is derived as a function of moduli fields $T^{i}$ and the scale $μ^2=1/(k+2)$ which induced by the non-zero background fields. The spectrum of string excitations has a non-zero mass gap $μ^2$ and in the weak curvature limit ($μ$ small) $μ^2$ plays the role of a well defined infrared regulator, consistent with modular invariance, gauge invariance, supersymmetry and chirality. The effects of a covariantly constant chomo-magnetic field $B$ as well as additional curvature can be derived exactly up to one string-loop level. Thus, the one-loop corrections to all couplings (gravitational, gauge and Yukawas) are unambiguously computed and are finite both in the Ultra-Violet and the Infra-Red regime. These corrections are necessary for quantitative string superunification predictions at low energies. Similar calculations are done in the effective field theory. The one-loop corrections to the couplings are also found to satisfy Infrared Flow Equations.

hep-th↗

arXiv1995

Infrared-Regulated String Theory and Loop Corrections to Coupling Constants

Exact superstring solutions are constructed in 4-D space-time, with positive curvature and non-trivial dilaton and antisymmetric tensor fields. The full spectrum of string excitations is derived as a function of moduli fields $T^{i}$ and the scale $μ^2=1/(k+2)$ which is induced by the non-zero background fields. The spectrum of string excitations has a non-zero mass gap $μ^2$ and in the weak curvature limit ($μ$ small) $μ^2$ plays the role of a well defined infrared regulator, consistent with modular invariance, gauge invariance, supersymmetry and chirality. The effects of a covariantly constant (chomo)magnetic field $H$ as well as additional curvature can be derived exactly up to one string-loop level. Thus, the one-loop corrections to all couplings (gravitational, gauge and Yukawas) are unambiguously computed and are finite both in the UltraViolet and the InfraRed regime. These corrections are necessary for quantitative string superunification predictions at low energies. The one-loop corrections to the couplings are also found to satisfy Infrared Flow Equations. Having in our disposal an exact description which goes beyond the leading order in the $α'$-expansion or the linearized approximation in the magnetic field, we find interesting clues about the physics of string theory in strong gravitational and magnetic fields. In particular, the nature of gravitational or magnetic instabilities is studied.

hep-th↗

arXiv1995

Infrared Regularization of Superstring Theory and the One-Loop Calculation of Coupling Constants

Infrared regularized versions of 4-D N=1 superstring ground states are constructed by curving the spacetime. A similar regularization can be performed in field theory. For the IR regularized string ground states we derive the exact one-loop effective action for non-zero U(1) or chromo-magnetic fields as well as gravitational and axionic-dilatonic fields. This effective action is IR and UV finite. Thus, the one-loop corrections to all couplings (gravitational, gauge and Yukawas) are unabiguously computed. These corrections are necessary for quantitative string superunification predictions at low energies. The one-loop corrections to the couplings are also found to satisfy Infrared Flow Equations.

hep-th↗

arXiv1995

Possible dynamical determination of $m_t$, $m_b$ and $m_τ

Motivated by four-dimensional superstring models, we consider the possibility of treating the Yukawa couplings of the Minimal Supersymmetric Standard Model (MSSM) as dynamical variables of the effective theory at the electroweak scale. Assuming bottom-tau unification, we concentrate on the top and bottom Yukawa couplings, and find that minimizing the effective potential drives them close to an effective infrared fixed line. Requiring an acceptable bottom-top mass ratio leads in principle to an additional constraint on the MSSM parameter space. As a by-product, we give new approximate analytical solutions of the renormalization group equations for the MSSM parameters.

hep-ph↗

arXiv1993

Construction of String Solutions around Non-trivial Backgrounds

We present a way of constructing string solutions around non-trivial gravitational backgrounds. The proposed solutions are constructed using $N = 4$ superconformal building blocks with $\hat c = 4$. We give two different and inequivalent realizations of non-trivial four-dimensional subspaces, and we show the emergence of the $N = 4$ globally defined superconformal symmetry. The existence of $N = 4$ world-sheet symmetry stabilizes our solutions and implies in target space a number of covariantized supersymmetries around space-time dependent gravitational and dilaton backgrounds.

hep-th↗