Instantons and SL(2,R) Symmetry in Type IIB Supergravity

We discuss the relation between the dual formulations of Type IIB supergravity emphasizing the differences between Lorentz and Euclidean signature. We demonstrate how the SL(2,R) symmetry of the usual action is manifested in the solution of the equations of motion with Euclidean signature for the dual theory.Comment: 4 pages, no figure

The COOH-terminal domain of agrin signals via a synaptic receptor in central nervous system neurons

Agrin is a motor neuron–derived factor that directs formation of the postsynaptic apparatus of the neuromuscular junction. Agrin is also expressed in the brain, raising the possibility that it might serve a related function at neuron–neuron synapses. Previously, we identified an agrin signaling pathway in central nervous system (CNS) neurons, establishing the existence of a neural receptor that mediates responses to agrin. As a step toward identifying this agrin receptor, we have characterized the minimal domains in agrin that bind and activate it. Structures required for agrin signaling in CNS neurons are contained within a 20-kD COOH-terminal fragment of the protein. Agrin signaling is independent of alternative splicing at the z site, but requires sequences that flank it because their deletion results in a 15-kD fragment that acts as an agrin antagonist. Thus, distinct regions within agrin are responsible for receptor binding and activation. Using the minimal agrin fragments as affinity probes, we also studied the expression of the agrin receptor on CNS neurons. Our results show that both agrin and its receptor are concentrated at neuron–neuron synapses. These data support the hypothesis that agrin plays a role in formation and/or function of CNS synapses

Type 0A 2D Black Hole Thermodynamics and the Deformed Matrix Model

Recently, it has been proposed that the deformed matrix model describes a two-dimensional type 0A extremal black hole. In this paper, the thermodynamics of 0A charged non-extremal black holes is investigated. We observe that the free energy of the deformed matrix model to leading order in 1/q can be seen to agree to that of the extremal black hole. We also speculate on how the deformed matrix model is able to describe the thermodynamics of non-extremal black holes.Comment: 12 page

The MSSM fine tuning problem: a way out

As is well known, electroweak breaking in the MSSM requires substantial fine-tuning, mainly due to the smallness of the tree-level Higgs quartic coupling, lambda_tree. Hence the fine tuning is efficiently reduced in supersymmetric models with larger lambda_tree, as happens naturally when the breaking of SUSY occurs at a low scale (not far from the TeV). We show, in general and with specific examples, that a dramatic improvement of the fine tuning (so that there is virtually no fine-tuning) is indeed a very common feature of these scenarios for wide ranges of tan(beta) and the Higgs mass (which can be as large as several hundred GeV if desired, but this is not necessary). The supersymmetric flavour problems are also drastically improved due to the absence of RG cross-talk between soft mass parameters.Comment: 28 pages, 9 PS figures, LaTeX Published versio

A Dynamic Analysis of the Rotation Mechanism for Conformational Change in F1-ATPase

AbstractMolecular dynamics trajectories for the bovine mitochondrial F1-ATPase are used to demonstrate the motions and interactions that take place during the elementary (120° rotation) step of the γ subunit. The results show how rotation of the γ subunit induces the observed structural changes in the catalytic β subunits. Both steric and electrostatic interactions contribute. An “ionic track” of Arg and Lys residues on the protruding portion of the γ subunit plays a role in guiding the motions of the β subunits. Experimental data for mutants of the DELSEED motif and the hinge region are interpreted on the basis of the molecular dynamics results. The trajectory provides a unified dynamic description of the coupled subunit motions involved in the 120° rotation cycles of F1-ATPase

Neutrino-induced lepton flavor violation in gauge-mediated supersymmetry breaking

Gauge-mediated supersymmetry breaking is known to greatly suppress flavor changing neutral current effects. However, we show that gauge mediation in the context of leptogenesis implies potentially large lepton flavor violating signals. If the heavy right-handed neutrinos that participate in leptogenesis are lighter than the messenger scale of gauge mediation, they will induce flavor off-diagonal masses to the sleptons which in turn can induce large effects in mu to e gamma, tau to mu gamma, and mu-e conversion in nuclei. We demonstrate this result and compute numerically the lepton-flavor violating decay and conversion rates in scenarios of direct gauge mediation.Comment: 18 pages, 5 figure

Super-conservative interpretation of muon g-2 results applied to supersymmetry

The recent developments in theory and experiment related to the anomalous magnetic moment of the muon are applied to supersymmetry. We follow a very cautious course, demanding that the supersymmetric contributions fit within five standard deviations of the difference between experiment and the standard model prediction. Arbitrarily small supersymmetric contributions are then allowed, so no upper bounds on superpartner masses result. Nevertheless, non-trivial exclusions are found. We characterize the substantial region of parameter space ruled out by this analysis that has not been probed by any previous experiment. We also discuss some implications of the results for forthcoming collider experiments.Comment: 10 pages, latex, 3 fig

Horava-Witten Stability: eppur si muove

We construct exact time-dependent solutions of the supergravity equations of motion in which two initially non-singular branes, one with positive and the other with negative tension, move together and annihilate each other in an all-enveloping spacetime singularity. Among our solutions are the Horava-Witten solution of heterotic M-theory and a Randall-Sundrum I type solution, both of which are supersymmetric, i.e. BPS, in the time-independent case. In the absence of branes our solutions are of Kasner type, and the source of instability may ascribed to a failure to stabilise some of the modulus fields of the compactification. It also raises questions about the viability of models based on some sorts of negative tension brane.Comment: Latex, 22 pages, extended discussion of the global spacetime structure, and reference adde

On Yukawa quasi-unification with mu<0

Although recent data on the muon anomalous magnetic moment strongly disfavor the constrained minimal supersymmetric standard model with mu<0, they cannot exclude it because of theoretical ambiguities. We consider this model supplemented by a Yukawa quasi-unification condition which allows an acceptable b-quark mass. We find that the cosmological upper bound on the lightest sparticle relic abundance is incompatible with the data on the branching ratio of b-->s gamma, which is evaluated by including all the next-to-leading order corrections. Thus, this scheme is not viable.Comment: 4 pages including 3 figures, Revte