M-Phenomenology

Recent developments involving strongly coupled superstrings are discussed from a phenomenological point of view. In particular, strongly coupled $E_8\times E'_8$ is described as an appropriate long-wavelength limit of M-theory, and some generic phenomenological implications are analyzed, including a long sought downward shift of the string unification scale and a novel way to break supersymmetry. A specific scenario is presented that leads to a rather light, and thus presently experimentally testable, sparticle spectrum.Comment: 22 pages, 2 figure

On a possible connection of non-critical strings to certain aspects of quantum brain function

We review certain aspects of brain function which could be associated with non-critical (Liouville) string theory. In particular we simulate the physics of brain microtubules (MT) by using a (completely integrable) non-critical string, we discuss the collapse of the wave function as a result of quantum gravity effects due to abrupt conformational changes of the MT protein dimers, and we propose a new mechanism for memory coding.Comment: Invited talk by D.V. Nanopoulos at the `four-seas conference', Trieste (Italy), 25 June-1 July 1995; latex file, 9 pages, one macro: 4seas95.sty, available from archive

Flipped Cryptons and the UHECRs

Cryptons are metastable bound states of fractionally-charged particles that arise generically in the hidden sectors of models derived from heterotic string. We study their properties and decay modes in a specific flipped SU(5) model with long-lived four-particle spin-zero bound states called {\it tetrons}. We show that the neutral tetrons are metastable, and exhibit the tenth-order non-renormalizable superpotential operators responsible for their dominant decays. By analogy with QCD, we expect charged tetrons to be somewhat heavier, and to decay relatively rapidly via lower-order interactions that we also exhibit. The expected masses and lifetimes of the neutral tetrons make them good candidates for cold dark matter (CDM), and a potential source of the ultra-high energy cosmic rays (UHECRs) which have been observed, whereas the charged tetrons would have decayed in the early Universe.Comment: 8 Pages RevTex. New version with expanded introduction to flipped SU(5). Accepted for publication in PR

The Electroweak Phase Transition in Minimal Supergravity Models

We have explored the electroweak phase transition in minimal supergravity models by extending previous analysis of the one-loop Higgs potential to include finite temperature effects. Minimal supergravity is characterized by two higgs doublets at the electroweak scale, gauge coupling unification, and universal soft-SUSY breaking at the unification scale. We have searched for the allowed parameter space that avoids washout of baryon number via unsuppressed anomalous Electroweak sphaleron processes after the phase transition. This requirement imposes strong constraints on the Higgs sector. With respect to weak scale baryogenesis, we find that the generic MSSM is {\it not} phenomenologically acceptable, and show that the additional experimental and consistency constraints of minimal supergravity restricts the mass of the lightest CP-even Higgs even further to m_h\lsim 32\GeV (at one loop), also in conflict with experiment. Thus, if supergravity is to allow for baryogenesis via any other mechanism above the weak scale, it {\it must} also provide for B-L production (or some other `accidentally' conserved quantity) above the electroweak scale. Finally, we suggest that the no-scale flipped $SU(5)$ supergravity model can naturally and economically provide a source of B-L violation and realistically account for the observed ratio $n_B/n_\gamma\sim 10^{-10}$.Comment: 14 pages (not including two postscript figures available upon request

Testing Quantum Mechanics in the Neutral Kaon System

The neutral kaon system is a sensitive probe of quantum mechanics. We revive a parametrization of non-quantum-mechanical effects that is motivated by considerations of the nature of space-time foam, and show how it can be constrained by new measurements of $K_L \rightarrow 2\pi$ and $K_{L,S}$ semileptonic decays at LEAR or a $\phi$ factory.Comment: 10 page

Liouville Cosmology

Liouville string theory is a natural framework for discussing the non-equilibrium evolution of the Universe. It enables non-critical strings to be treated in mathematically consistent manner, in which target time is identified with a world-sheet renormalization-group scale parameter, preserving target-space general coordinate invariance and the existence of an S-matrix. We review our proposals for a unified treatment of inflation and the current acceleration of the Universe. We link the current acceleration of the Universe with the value of the string coupling. In such a scenario, the dilaton plays an essential background role, driving the acceleration of the Universe during the present era after decoupling as a constant during inflation.Comment: 23 pages latex, 2 eps figures, contribution to the proceedings of the Dark 2004 conference, College Station, October 200

M-Theory Model-Building and Proton Stability

We study the problem of baryon stability in M theory, starting from realistic four-dimensional string models constructed using the free-fermion formulation of the weakly-coupled heterotic string. Suitable variants of these models manifest an enhanced custodial gauge symmetry that forbids to all orders the appearance of dangerous dimension-five baryon-decay operators. We exhibit the underlying geometric (bosonic) interpretation of these models, which have a $Z_2 \times Z_2$ orbifold structure similar, but not identical, to the class of Calabi-Yau threefold compactifications of M and F theory investigated by Voisin and Borcea. A related generalization of their work may provide a solution to the problem of proton stability in M theory.Comment: 14 pages. Standard Late

Is Nothing Sacred? Vacuum Energy, Supersymmetry and Lorentz Breaking from Recoiling D branes

Classical superstring vacua have zero vacuum energy and are supersymmetric and Lorentz-invariant. We argue that all these properties may be destroyed when quantum aspects of the interactions between particles and non-perturbative vacuum fluctuations are considered. A toy calculation of string/D-brane interactions using a world-sheet approach indicates that quantum recoil effects - reflecting the gravitational back-reaction on space-time foam due to the propagation of energetic particles - induce non-zero vacuum energy that is linked to supersymmetry breaking and breaks Lorentz invariance. This model of space-time foam also suggests the appearance of microscopic event horizons.Comment: 28 pages LaTeX, 5 eps figures, talk presented by DVN at 4th International Symposium On Sources And Detection Of Dark Matter In The Universe (DM 2000), Marina del Rey, California, 20-23 Feb 200

The String Universe: High TcT_c Superconductor or Quantum Hall Conductor?

Our answer is the latter. Space-time singularities, including the initial one, are described by world-sheet topological Abelian gauge theories with a Chern-Simons term. Their effective $N=2$ supersymmetry provides an initial fixed point where the Bogomolny bound is saturated on the world-sheet, corresponding to an extreme Reissner-Nordstrom solution in space-time. Away from the singularity the gauge theory has world-sheet matter fields, bosons and fermions, associated with the generation of target space-time. Because the fermions are complex (cf the Quantum Hall Effect) rather than real (cf high-$T_c$ superconductors) the energetically-preferred vacuum is not parity or time-reversal invariant, and the associated renormalization group flow explains the cosmological arrow of time, as well as the decay of real or virtual black holes, with a monotonic increase in entropy.Comment: 19 page