Stringy Instanton Effects in Models with Rigid Magnetised D-branes

We compute instantonic effects in globally consistent T^6/Z2xZ2 orientifold models with discrete torsion and magnetised D-branes. We consider fractional branes and instantons wrapping the same rigid cycles. We clarify and analyse in detail the low-energy effective action on D-branes in these models. We provide explicit examples where instantons induce linear terms in the charged fields, or non-perturbative mass terms are generated. We also find examples where the gauge theory on fractional branes has conformal symmetry at one-loop, broken by instantonic mass terms at a hierarchically small energy scale.Comment: 60 pages. Refs added. Typos corrected in some eqs. Modified comments in subsection 4.

Adventures in Thermal Duality (II): Towards a Duality-Covariant String Thermodynamics

In a recent companion paper, we observed that the rules of ordinary thermodynamics generally fail to respect thermal duality, a symmetry of string theory under which the physics at temperature T is related to the physics at the inverse temperature 1/T. Even when the free energy and internal energy exhibit the thermal duality symmetry, the entropy and specific heat are defined in such a way that this symmetry is destroyed. In this paper, we propose a modification of the traditional definitions of these quantities, yielding a manifestly duality-covariant thermodynamics. At low temperatures, these modifications produce "corrections" to the standard definitions of entropy and specific heat which are suppressed by powers of the string scale. These corrections may nevertheless be important for the full development of a consistent string thermodynamics. We find, for example, that the string-corrected entropy can be smaller than the usual entropy at high temperatures, suggesting a possible connection with the holographic principle. We also discuss some outstanding theoretical issues prompted by our approach.Comment: 31 pages, 6 figures, 1 conversatio

Non-perturbative Vacuum Destabilization and D-brane Dynamics

We analyze the process of string vacuum destabilization due to instanton induced superpotential couplings which depend linearly on charged fields. These non-perturbative instabilities result in potentials for the D-brane moduli and lead to processes of D-brane recombination, motion and partial moduli stabilization at the non-perturbative vacuum. By using techniques of D-brane instanton calculus, we explicitly compute this scalar potential in toroidal orbifold compactifications with magnetized D-branes by summing over the possible discrete instanton configurations. We illustrate explicitly the resulting dynamics in globally consistent models. These instabilities can have phenomenological applications to breaking hidden sector gauge groups, open string moduli stabilization and supersymmetry breaking. Our results suggest that breaking supersymmetry by Polonyi-like models in string theory is more difficult than expected.Comment: 61 pages, 6 figures, 5 tables; Minor corrections, version published in JHE

SU(5) orientifolds, Yukawa couplings, Stringy Instantons and Proton Decay

37 pagesWe construct a large class of SU(5) orientifold vacua with tadpole cancellation both for the standard and the flipped case. We give a general analysis of superpotential couplings up to quartic order in orientifold vacua and identify the properties of needed Yukawa couplings as well as the baryon number violating couplings. We point out that successful generation of the perturbatively forbidden Yukawa couplings entails a generically disastrous rate for proton decay from an associated quartic term in the superpotential, generated from the same instanton effects. We search for the appropriate instanton effects that generate the missing Yukawa couplings in the SU(5) vacua we constructed and find them in a small subset of them

Altered Erythrocyte CR1 Binding Kinetics Compensate for Decreased Binding Capacity in Rheumatoid Arthritis

Summary: Patients with rheumatoid arthritis have decreased numbers of CR1 per erythrocyte and decreased binding of immune complexes to erythrocytes. Overall erythrocyte immune complex binding activity depends on both the number and the binding kinetics of CR13). We measured kinetic parameters for the interaction between a complement-containing dsDNA: anti-dsDNA probe and erythrocytes in patients with rheumatoid arthritis and normal controls. The results indicate that: 1) the maximum quantity of immune complexes bound per erythrocyte was significantly decreased in rheumatoid arthritis compared with normal controls (p < 0.009); 2) the steady state binding constant, Kss, and the association rate constant for binding of immune complexes to erythrocytes, ka, were significantly increased in rheumatoid arthritis versus normal controls (p < 0.0001 and 0.002 respectively); 3) the dissociation rate constant for the release of bound immune complexes from erythrocytes, kd, was slightly smaller in rheumatoid arthritis but this difference was not statistically significant; and 4) the energies of activation for the association and dissociation reactions, Eaa, and Ead, did not differ between the two groups. These data confirm that while the maximum quantity of immune complexes bound per erythrocyte is decrease