119162863
Bouncing universe and non-BPS branes
We describe string frame bouncing universe scenarios involving the creation and annihilation of a non-BPS D9-brane in type IIA superstring theory. We find several classes of solutions, in which the bounce is driven by the tachyon dynamics of the non-BPS brane. The metric and dilaton during the bounce are consistently described in terms of the lowest order effective action. The bounce solutions interpolate between contracting and expanding pre-big bang (or post-big bang) solutions. The singular behavior of our bounce solutions is the same as that of the pre-big bang (or post-big bang) solution.
18213590
Dark matter in supersymmetric models with axino LSP in Randall-Sundrum II brane model
The axino dark matter hypothesis in RSII brane model is studied. Within the framework of CMSSM we assume that the lightest neutralino or stau is the NLSP, and that the axino production has a single contribution from the NLSP decay. It is found that the axino can play the role of dark matter in the universe and we determine what the axino mass should be for different values of the five-dimensional Planck mass. An upper bound is obtained for the latter.
197492266
Big-Bang Nucleosynthesis and neutralino dark matter in modified gravity
In the present work the primordial Big-Bang Nucleosynthesis (BBN) and neutralino dark matter are discussed in a certain class of modified gravitational theories, namely $f(R)$ gravity. We determine the conditions under which the theoretical predictions for $^{4}$He abundance and for the relic abundance of the neutralino dark matter are in agreement with the observations. Our results show that this class of gravitational models considered here is allowed to be only slightly different from Einstein's general relativity.
18228310
The new ekpyrotic ghost
The new ekpyrotic scenario attempts to solve the singularity problem by involving violation of the null energy condition in a model which combines the ekpyrotic/cyclic scenario with the ghost condensate theory and the curvaton mechanism of production of adiabatic perturbations of the metric. The Lagrangian of this theory, as well as of the ghost condensate model, contains a term with higher derivatives, which was added to the theory to stabilize its vacuum state. We found that this term may affect the dynamics of the cosmological evolution. Moreover, after a proper quantization, this term results in the existence of a new ghost field with negative energy, which leads to a catastrophic vacuum instability. We explain why one cannot treat this dangerous term as a correction valid only at small energies and momenta below some UV cutoff, and demonstrate the problems arising when one attempts to construct a UV completion of this theory.
118383938
One-loop Kähler metric of D-branes at angles
A bstractWe evaluate string one-loop contributions to the Kähler metric of D-brane moduli (positions and Wilson lines), in toroidal orientifolds with branes at angles. Contributions due to bulk states in the loop are known, so we focus on the contributions due to states localized at intersections of orientifold images. We show that these quantum corrections vanish. This does not follow from the usual nonrenormalization theorems of supersymmetric field theory.
119301594
Attractor scenarios and superluminal signals in k-essence cosmology
Cosmological scenarios with k-essence are invoked in order to explain the observed late-time acceleration of the Universe. These scenarios avoid the need for fine-tuned initial conditions (the 'coincidence problem') because of the attractorlike dynamics of the k-essence field {phi}. It was recently shown that all k-essence scenarios with Lagrangians p=L(X){phi}{sup -2}, where X{identical_to}(1/2){phi}{sub ,{mu}}{phi}{sup ,{mu}}, necessarily involve an epoch where perturbations of {phi} propagate faster than light (the 'no-go theorem'). We carry out a comprehensive study of attractorlike cosmological solutions ('trackers') involving a k-essence scalar field {phi} and another matter component. The result of this study is a complete classification of k-essence Lagrangians that admit asymptotically stable tracking solutions, among all Lagrangians of the form p=K({phi})L(X). Using this classification, we select the class of models that describe the late-time acceleration and avoid the coincidence problem through the tracking mechanism. An analogous 'no-go theorem' still holds for this class of models, indicating the existence of a superluminal epoch. In the context of k-essence cosmology, the superluminal epoch does not lead to causality violations. We discuss the implications of superluminal signal propagation for possible causality violations in Lorentz-invariant field theories.
120126738
Multiparticle Production in the Central Region
The mechanism of multiparticle production in the central region is discussed in the framework of the independent-emission picture and in that of the fragmentation picture. It is argued that the study of a certain moment ratio and distribution ratio may be helpful to differentiate these two pictures. The intersecting-storage-rings multi-$\ensuremath{\gamma}$ experiment of the Brookhaven-Roma Collaboration is discussed in this connection. In order to illustrate some general features of the fragmentation picture, the model recently proposed by Chou and Yang for charge transfer is applied to the multi-$\ensuremath{\gamma}$ production process.
117842087
An Upgrade Proposal from the PHENIX Collaboration
In this document the PHENIX collaboration proposes a major upgrade to the PHENIX detector at the Relativistic Heavy Ion Collider. This upgrade, sPHENIX, enables an extremely rich jet and beauty quarkonia physics program addressing fundamental questions about the nature of the strongly coupled quark-gluon plasma (QGP), discovered experimentally at RHIC to be a perfect fluid. The startling dynamics of the QGP on fluid-like length scales is an emergent property of quantum chromodynamics (QCD), seemingly implicit in the Lagrangian but stubbornly hidden from view. QCD is an asymptotically free theory, but how QCD manifests as a strongly coupled fluid with specific shear viscosity near $T_C$, as low as allowed by the uncertainty principle, is as fundamental an issue as that of how confinement itself arises.
122313966
Chiral SU(2) X SU(2) symmetry in the $pi$K scattering
125442396
THE UPSILON SPECTRUM IN A POTENTIAL MODEL WITH RELATIVISTIC CORRECTIONS
121196804
CERN beam test of silicon-tungsten calorimeter test module
PIN diode silicon sensors with low leakage current were developed as 4×4 pixel arrays from 5 inch wafers. A test module of silicon-tungsten calorimeter was designed, built using the sensors, and tested with high energy beam of electron, muon, and hadrons for the study of its application at the future linear collider. The construction of the test module and the results of the beam test are discussed.