We study the neutral current flavor changing rare decay mode $\overrightarrow{B}{X}_s+$ missing energy within the framework of theories with large extra spatial dimensions. The corresponding standard model signature is $\overrightarrow{B}{X}_s+\nu \overline{\nu }.$ But in theories with large extra dimensions, it is possible to have scalars and gravitons in the final state making it quite distinct from any other scenario where there are no gravitons and the scalars are far too much heavier than the B meson to be present as external particles. We give an estimate of the branching ratio for such processes for different values of the number of extra dimensions and the scale of the effective theory. The predicted branching ratios can be comparable with the standard model rate for a restrictive choice of the parameters.

Kachru, Kallosh, Linde, and Trivedi recently constructed a four-dimensional de Sitter compactification of type IIB string theory, which they showed to be metastable in agreement with general arguments about de Sitter spacetimes in quantum gravity. In this paper, we describe how discrete flux choices lead to a closely spaced set of vacua and explore various decay channels. We find that in many situations NS5-brane mediated decays which exchange NSNS 3-form flux for D3-branes are comparatively very fast.

We study the low-lying excitations of type IIA superstring theory in a plane wave background with 24 supersymmetries. In the light-cone gauge, the superstring action has $\mathcal{N}=(4,4)\mathrm{}$ supersymmetry and is exactly solvable, since it is quadratic in superstring coordinates. We obtain explicitly the spectrum of the type IIA supergravity fluctuation modes in the plane wave background and give its correspondence with the spectrum of string states from the zero-mode sector of the light-cone superstring Hamiltonian.

We analyze perturbative aspects of gauged matrix models, including those where classically the gauge symmetry is partially broken. Ghost fields play a crucial role in the Feynman rules for these vacua. We use this formalism to elucidate the fact that nonperturbative aspects of $\mathcal{N}=1\mathrm{}$ gauge theories can be computed systematically using perturbative techniques of matrix models, even if we do not possess an exact solution for the matrix model. As examples we show how the Seiberg-Witten solution for $\mathcal{N}=2\mathrm{}$ gauge theory, the Montonen-Olive modular invariance for $\mathcal{N}{=1\mathrm{}}^{*},$ and the superpotential for the Leigh-Strassler deformation of $\mathcal{N}=4\mathrm{}$ can be systematically computed in perturbation theory of the matrix model or gauge theory (even though in some of these cases an exact answer can also be obtained by summing up planar diagrams of matrix models).

We consider supersymmetric sigma models on the Kähler target spaces, with a twisted mass. The Kähler spaces are assumed to have holomorphic Killing vectors. The introduction of a superpotential of a special type is known to be consistent with $\mathcal{N}=2\mathrm{}$ superalgebra (Alvarez-Gaumé and Freedman). We show that the algebra acquires central charges in the anticommutators $\{Q_L{,Q}_L\}$ and $\{Q_R{,Q}_R\}.$ These central charges have no parallels, and they can exist only in two dimensions. The central extension of the $\mathcal{N}=2\mathrm{}$ superalgebra we find paves the way to a novel phenomenon—spontaneous breaking of a part of the supersymmetry. In the general case, 1/2 of the supersymmetry is spontaneously broken (the vacuum energy density is positive), while the remaining 1/2 is realized linearly. In the model at hand, the standard fermion number is not defined, so that the Witten index as well as the Cecotti-Fendley-Intriligator-Vafa index are useless. We show how to construct an index for counting short multiplets in internal algebraic terms which is well defined in spite of the absence of the standard fermion number. Finally, we outline the derivation of the quantum anomaly in the anticommutator $\{Q_L{,Q}_R\}.$

A theory for studying the dynamic scaling properties of branes and relativistic topological defect networks is presented. The theory, based on a relativistic version of the level set method, well known in other contexts, possesses self-similar “scaling” solutions, for which one can calculate many quantities of interest. Here, the length and area densities of cosmic strings and domain walls are calculated in Minkowski space, and radiation, matter, and curvature-dominated Friedmann-Robertson-Walker cosmologies with two and three space dimensions. The scaling exponents agree with the naive ones based on dimensional analysis, except for cosmic strings in three-dimensional Minkowski space, which are predicted to have a logarithmic correction to the naive scaling form. The scaling amplitudes of the length and area densities are a factor of approximately 2 lower than the results from numerical simulations of classical field theories. An expression for the length density of strings in the condensed matter literature is corrected.

Warped extra dimensions allow a novel way of solving the hierarchy problem, with all fundamental mass parameters of the theory naturally of the order of the Planck scale. The observable value of the Higgs vacuum expectation value is redshifted, due to the localization of the Higgs field in the extra dimension. It has been recently observed that, when the gauge fields propagate in the bulk, unification of the gauge couplings may be achieved. Moreover, the propagation of fermions in the bulk allows for a simple solution to potentially dangerous proton decay problems. However, bulk gauge fields and fermions pose a phenomenological challenge, since they tend to induce large corrections to the precision electroweak observables. In this article, we study in detail the effect of gauge and fermion fields propagating in the bulk in the presence of gauge brane kinetic terms compatible with gauge coupling unification, and we present ways of obtaining a consistent description of experimental data, while allowing values of the first Kaluza-Klein mode masses of the order of a few TeV.

We calculate the tree-level electroweak precision constraints on a wide class of little Higgs models including variations of the littlest Higgs SU(5)/SO(5), SU(6)/Sp(6), and $\mathrm{SU}{\mathrm{}\left(4\right)\mathrm{}}^4/\mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}^4$ models. By performing a global fit to the precision data we find that for generic regions of the parameter space the bound on the symmetry breaking scale f is several TeV, where we have kept the normalization of f constant in the different models. For example, the “minimal” implementation of SU(6)/Sp(6) is bounded by $f>\mathrm{}3.0\mathrm{}\mathrm{TeV}$ throughout most of the parameter space, and $\mathrm{SU}{\mathrm{}\left(4\right)\mathrm{}}^4/\mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}^4$ is bounded by $f^2\equiv f_1^2{+f}_2^2>(4.2\mathrm{}\mathrm{TeV}{)}^2.$ In certain models, such as $\mathrm{SU}{\mathrm{}\left(4\right)\mathrm{}}^4/\mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}^4,$ a large f does not directly imply a large amount of fine-tuning since the heavy-fermion masses that contribute to the Higgs boson mass can be lowered below f for a carefully chosen set of parameters. We also find that for certain models (or variations) there exist regions of parameter space in which the bound on f can be lowered into the range 1–2 TeV. These regions are typically characterized by a small mixing between heavy and standard model gauge bosons and a small (or vanishing) coupling between heavy U(1) gauge bosons and light fermions. Whether such a region of parameter space is natural or not is ultimately contingent on the UV completion.

We elaborate on previous results concerning the positivity of the Euclidean path integral measure for low-energy modes in dense fermionic matter. We show that the sign problem usually associated with fermions is absent if one considers only low-energy degrees of freedom. We describe a method for simulating dense QCD on the lattice and give a proof using rigorous inequalities that the color-flavor locked (CFL) phase is the true vacuum of three flavor, massless QCD. We also discuss applications to electronic systems in condensed matter, such as generalized Hubbard models.

The results of SIDIS experiments concerning the first moments of the polarized quark distributions are considered. The possible reasons for the deviation from the fundamental restrictions such as the Bjorken sum rule and the ways to properly improve the analysis of measured SIDIS asymmetries are discussed. The possibility of a broken polarized sea scenario is analyzed.

We compute the one-loop supersymmetric (SUSY) contributions to the weak charges of the electron ${(Q}_W^e),$ proton ${(Q}_W^p),$ and cesium nucleus ${(Q}_W^{\mathrm{Cs}})$ in the minimal supersymmetric standard model (MSSM). Such contributions can generate several percent corrections to the corresponding standard model values. The magnitudes of the SUSY loop corrections to $Q_W^e$ and $Q_W^p$ are correlated over nearly all of the MSSM parameter space and result in an increase in the magnitudes of these weak charges. In contrast, the effects on $Q_W^{\mathrm{Cs}}$ are considerably smaller and are equally likely to increase or decrease its magnitude. Allowing for R-parity violation can lead to opposite sign relative shifts in $Q_W^e$ and $Q_W^p,$ normalized to the corresponding standard model values. A comparison of $Q_W^p$ and $Q_W^e$ measurements could help distinguish between different SUSY scenarios.

We calculate quantum corrections to the mass of the vortex in the $N=2\mathrm{}$ supersymmetric Abelian Higgs model in $2+1$ dimensions. We put the system in a box and apply zeta function regularization. The boundary conditions inevitably violate a part of the supersymmetries. The remaining supersymmetry is, however, enough to ensure isospectrality of relevant operators in bosonic and fermionic sectors. A nonzero correction to the mass of the vortex comes from finite renormalization of couplings.

We discuss the relation between the Polyakov loop and the chiral order parameter at finite temperature by using the Gocksch-Ogilvie model with fundamental or adjoint quarks. The model is based on the double expansion of strong coupling and large dimensionality on the lattice. In an analytic way, using the mean field approximation, we show that the confined phase must be accompanied by the spontaneous breaking of chiral symmetry for both fundamental and adjoint quarks. Then we proceed to numerical analyses to look into the coupled dynamics of the Polyakov loop and the chiral order parameter. In the case of fundamental quarks, the pseudocritical temperature inferred from the Polyakov loop behavior turns out to coincide with the pseudocritical temperature of the chiral phase transition. We discuss the physical implication of the coincidence of the pseudocritical temperatures in two extreme cases: one is deconfinement dominance and the other is chiral dominance. As for adjoint quarks, the deconfinement transition of first order persists and the chiral phase transition occurs at distinctly higher temperature than the deconfinement transition. The present model study gives us a plausible picture to understand the results from lattice QCD and aQCD simulations.

In the 3+1 framework of the Einstein equations for the case of a vanishing shift vector and arbitrary lapse, we calculate explicitly the four boundary equations arising from the vanishing of the projection of the Einstein tensor along the normal to the boundary surface of the initial-boundary value problem. Such conditions take the form of evolution equations along (as opposed to across) the boundary for certain components of the extrinsic curvature and for certain space derivatives of the three-metric. We argue that, in general, such boundary conditions do not follow necessarily from the evolution equations and the initial data, but need to be imposed on the boundary values of the fundamental variables. Using the Einstein-Christoffel formulation, which is strongly hyperbolic, we show how three of the boundary equations up to linear combinations should be used to prescribe the values of some incoming characteristic fields. Additionally, we show that the fourth one imposes conditions on some outgoing fields.

We explore numerically the evolution of a collapsing spherical shell of a charged, massless scalar field. We obtain an external Reissner-Nordström space-time, and an inner space-time that is bounded by a singularity on the Cauchy horizon. We compare these results with previous analyses and discuss some of the numerical problems encountered.

In supersymmetric models a gluino can decay into $\mathrm{tb}{\tilde{\chi }}_1^{\pm }$ through a top squark (stop) or a sbottom. The decay chain produces an edge structure in the $m_{\mathrm{tb}}$ distribution. Monte Carlo simulation studies show that the end point and edge height would be measured at the CERN LHC by using a sideband subtraction technique. The stop and sbottom masses as well as their decay branching ratios are constrained by the measurement. We study interpretations of the measurement in the minimal supergravity model. We also study the gluino decay into $\mathrm{tb}{\tilde{\chi }}_2^{\pm }$ as well as the influence of the stop left-right mixing on the $m_{\mathrm{bb}}$ distribution of the tagged tb events.

Interference between Cabibbo-Kobayashi-Maskawa (CKM) favored $\overrightarrow{b}cūd$ and doubly-CKM-suppressed $\overline{b}\to ūc\overline{d}$ amplitudes in final states used for B-flavor tagging gives deviations from the standard time evolution assumed in CP-violation measurements at B factories producing coherent $B^0{B}^0$ pairs. We evaluate these deviations for the standard time-dependent CP-violation measurements, the uncertainties they introduce in the measured quantities, and give suggestions for minimizing them. The uncertainty in the measured CP asymmetry for CP eigenstates is $\approx 2\%$ or less. The time-dependent analysis of $D^{*}\pi ,$ proposed for measuring $\sin (2\mathrm{}\beta +\gamma ),$ must incorporate possible tag-side interference, which could produce asymmetries as large as the expected signal asymmetry.

In the framework of the weighted superposition mechanism of different classes of minimum bias events (or substructures), described by the negative binomial multiplicity distribution, in possible scenarios for pp collisions in the TeV energy domain, we explore global properties of an eventual new class of events, characterized by high hadron and clan densities, to be added to the soft (without minijets) and semihard (with minijets) ones. It turns out that the main signal of the mentioned new physical expectations at 14 TeV c.m. energy would be an “elbow structure” in the tail of the total charged particle multiplicity distribution in complete disagreement with the second shoulder structure predicted by PYTHIA Monte Carlo calculations: a challenging problem for new experimental work.

We explore models with additional right-handed gauge bosons that couple predominantly to the third generation in the context of $b\overline{b}$ production at CERN LEP. In particular we investigate potential new contributions to $\delta g_{\mathrm{Rb}}$ that are needed if the measured $A_{\mathrm{FB}}^b$ at the Z peak is interpreted as a signal of new physics. We identify two sources of large $\delta g_{\mathrm{Rb}}$ corrections: $Z-Z^{\prime }$ mixing at the tree level, and one-loop effects from a new ${\mathrm{SU}}_R\mathrm{}\left(2\right)\mathrm{}$ triplet of gauge bosons. We find that the latter can contribute to $\delta g_{\mathrm{Rb}}$ at the 1% level. We place bounds on the mass of the additional $Z^{\prime }$ gauge boson that occurs in these models using the $R_b$ measurements from LEP-II. We find that even in cases where the $Z^{\prime }$ couples almost exclusively to the b and t quarks, masses lighter than about 500 GeV are already excluded.