Related papers: The non-topological $Z^\prime$ string in the 331 m…
The weakly-coupled heterotic string is known to have problems of dilaton/moduli stabilization, supersymmetry breaking (by hidden-sector gaugino condensation), gauge coupling unification (or the Newton's constant), QCD axion, as well as…
In various supersymmetric extensions of the Standard Model there appear non-topological solitons due to the existence of U(1) global symmetries associated with Baryon and/or Lepton quantum numbers. Trilinear couplings (A-terms) in the…
In this paper we construct a string-like classical solution, the pion-string, in the linear sigma model. We then study the stability of the pion-string, and find that it is unstable in the parameter space allowed experimentally. We also…
We report results relating to the trinification scenario in some explicit string constructions that contain SU(3)^3 as a gauge symmetry. These models are obtained from symmetric Z_3 orbifolds of the SO(32) heterotic string with one discrete…
In the standard model, stabilization of a classically unstable cosmic string may occur through the quantum fluctuations of a heavy fermion doublet. We review numerical results from a semiclassical expansion in a reduced version of the…
We revisit the classical instability of closed strings in the Abelian Higgs model. The instability is expressed by a vanishing energy as the torus-like configuration shrinks to zero size. We treat the radius of the torus as a collective…
We study the minimal set of Higgs scalars, for models based on the local gauge group $SU(3)_c \otimes SU(3)_L \otimes U(1)_X$ which do not contain particles with exotic electric charges. We show that only two Higgs $SU(3)_L$ triplets are…
We consider the minimal U(1)' extension of the standard model (SM) with the classically conformal invariance, where an anomaly-free U(1)' gauge symmetry is introduced along with three generations of right-handed neutrinos and a U(1)' Higgs…
We point out that type I string theory in the presence of internal magnetic fields provides a concrete realization of split supersymmetry. To lowest order, gauginos are massless while squarks and sleptons are superheavy. We build such…
Is perturbative stability intimately tied with the existence of spacetime fermions in string theory in more than two dimensions? Type 0'B string theory in ten-dimensional flat space is a rare example of a non-tachyonic, non-supersymmetric…
Within a slightly simplified version of the electroweak standard model we investigate the stabilization of cosmic strings by fermion quantum fluctuations. Previous studies of quantum energies considered variants of the Nielsen-Olesen…
We construct a large class of non-supersymmetric AdS-like throat geometries in string theory by taking non-supersymmetric orbifolds of supersymmetric backgrounds. The scale of SUSY breaking is the AdS radius, and the dual field theory has…
We review the main results of our investigations motivated by the tadpole potentials of ten-dimensional strings with broken supersymmetry. While these are at best partial indications, it is hard to resist the feeling that they do capture…
The $SU(3)_L\otimes U(1)_X$ symmetry actually studied is directly broken to the electroweak symmetry $SU(2)_L\otimes U(1)_Y$ by a Higgs triplet, predicting a relevant new physics at TeV scale. This work argues, by contrast, that the higher…
We study the cosmology of a string derived supersymmetric flipped $SU(5)$ model in the context of free-fermionic heterotic constructions that allow full calculability of the effective supergravity in perturbation theory around the fermionic…
We investigate the low energy physics implications of a prototype quasi-realistic superstring model with an anomalous U(1). First, we present the techniques utilized to compute the mass spectrum and superpotential couplings at the string…
I investigate the role of nonrenormalizable terms, up to order N=8, in a superstring derived standard--like model. I argue that nonrenormalizable terms restrict the gauge symmetry, at the Planck scale, to be $SU(3)\times SU(2)\times…
We investigate the stability of the electroweak Z-string at high temperatures. Our results show that while finite temperature corrections can improve the stability of the Z-string, their effect is not strong enough to stabilize the Z-string…
We present a string-inspired/derived supergravity model based on the flipped $SU(5)\times U(1)$ structure supplemented by a minimal set of additional matter representations such that unification occurs at the string scale…
Tensionless string theory on AdS3 x S3 x T4, as captured by a free symmetric product orbifold, has a large set of conserved currents which can be usefully organised in terms of representations of a N=(4,4) supersymmetric higher spin…