Thermal corrections have an important effect on modulus stabilization leading to the existence of a maximal temperature, beyond which the compact dimensions decompactify. In this paper, we discuss the generality of our earlier analysis and apply it to the case of flux compactifications. The maximal temperature is again found to be controlled by the supersymmetry breaking scale, Tcrit - √m3/2MP. ©2005 IOP Publishing Ltd.

We construct a compactification of the heterotic string on an orbifold T6/ℤ6 leading to the standard model spectrum plus vector-like matter. The standard model gauge group is obtained as an intersection of three SO(10) subgroups of E8. Three families of SO(10) 16-plets are localized at three equivalent fixed points. Gauge coupling unification favours existence of an intermediate GUT which can have any dimension between five and ten. Various GUT gauge groups occur. For example, in six dimensions one can have E6 × SU(3), SU(4) × SU(4) × U(1)2 or SO(8) × SO(8), depending on which of the compact dimensions are large. The different higher-dimensional GUTs are 'dual' to each other. They represent different points in moduli space, with the same massless spectrum and ultraviolet completion. © 2005 Elsevier B.V. All rights reserved.

We describe in detail a Z6 orbifold compactification of the heterotic E8 × E8 string which leads to the (supersymmetric) Standard Model gauge group and matter content. The quarks and leptons appear as three 16-plets of SO (10), two of which are localized at fixed points with local SO (10) symmetry. The model has supersymmetric vacua without exotics at low energies and is consistent with gauge coupling unification. Supersymmetry can be broken via gaugino condensation in the hidden sector. The model has large vacuum degeneracy. Certain vacua with approximate B - L symmetry have attractive phenomenological features. The top quark Yukawa coupling arises from gauge interactions and is of the order of the gauge couplings. The other Yukawa couplings are suppressed by powers of Standard Model singlet fields, similarly to the Froggatt-Nielsen mechanism. © 2007 Elsevier B.V. All rights reserved.

We consider supersymmetric theories where the gravitino is the lightest superparticle (LSP). Assuming that the long-lived next-to-lightest superparticle (NSP) is a charged slepton, we investigate two complementary ways to prove the existence of supergravity in nature. The first is based on the NSP lifetime which in supergravity depends only on the Planck scale and the NSP and gravitino masses. With the gravitino mass inferred from kinematics, the measurement of the NSP lifetime will test an unequivocal prediction of supergravity. The second way makes use of the 3-body NSP decay. The angular and energy distributions and the polarizations of the final state photon and lepton carry the information on the spin of the gravitino and on its couplings to matter and radiation. © 2004 Elsevier B.V. All rights reserved.

We present a [FORMULA: SEE TEXT] orbifold compactification of the E8xE8 heterotic string which leads to the (supersymmetric) standard model gauge group and matter content. The quarks and leptons appear as three 16-plets of SO(10), whereas the Higgs fields do not form complete SO(10) multiplets. The model has large vacuum degeneracy. For generic vacua, no exotic states appear at low energies and the model is consistent with gauge coupling unification. The top quark Yukawa coupling arises from gauge interactions and is of the order of the gauge couplings, whereas the other Yukawa couplings are suppressed.

The spontaneous breaking of U(1)B−L around the scale of grand unification can simultaneously account for hybrid inflation, leptogenesis, and neutralino dark matter, thus resolving three major puzzles of particle physics and cosmology in a single predictive framework. The B−L phase transition also results in a network of cosmic strings. If strong and electroweak interactions are unified in an SO(10) gauge group, containing U(1)B−L as a subgroup, these strings are metastable. In this case, they produce a stochastic background of gravitational waves that evades current pulsar timing bounds, but features a flat spectrum with amplitude h2ΩGW∼10−8 at interferometer frequencies. Ongoing and future LIGO observations will hence probe the scale of B−L breaking.

We study the possibility of realizing the neutrino seesaw mechanism in the E(8) x E(8) heterotic string. In particular, we consider its Z6 orbifold compactifications leading to the supersymmetric standard model gauge group and matter content. We find that these models possess all the necessary ingredients for the seesaw mechanism, including the required Dirac Yukawa couplings and large Majorana mass terms. We argue that this situation is quite common in heterotic orbifolds. In contrast with the conventional seesaw of grand unified theories (GUTs), no large GUT representations are needed to generate the Majorana mass terms. The total number of right-handed neutrinos can be very large, up to O(100).