We compute supersymmetric QCD and supersymmetric electroweak corrections to the b and t quark masses and to the $\tau$ lepton mass in the presence of CP phases valid for all $\tan \beta .$ The analysis includes one loop diagrams arising from the exchange of gluinos, charginos and neutralinos. We find that the CP effects can change both the magnitude as well as the sign of the supersymmetric loop correction. In the region of parameter space studied we found that the numerical size of the correction to the b quark mass can be as large as 30 % and to the $\tau$ lepton mass as much as 5%. For the top quark mass the correction is typically less than a percent. These corrections are of importance in unified models since $b-\tau$ and $b-t-\tau$ unification is strongly affected by the size of these corrections. More generally these results will be of importance in analyses of quark-lepton textures with the inclusion of CP phases. Further, the analysis presented here is relevant in a variety of low energy phenomena where supersymmetric QCD and supersymmetric electroweak corrections on the b mass enter prominently in B physics, e.g., in processes such as $B_{s,d}^0\to l^{+}{l}^{-}.$

The annihilation of the $B_c$ meson to leptons and inclusive light hadrons is analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find that the decay mode, which escapes from the helicity suppression, contributes a sizable fraction width. The branching ratio due to the contributions from the color-singlet component of the $B_c$ meson can be of the order of ${10}^{-2}.$ The contributions from the color-octet components are estimated. With the consideration of the NRQCD velocity scaling rule, we find that the color-octet contributions are sizable too, especially in a certain phase space of the annihilation. They are greater than (or comparable to) those from the color-singlet component. A few observables on the spectrum of charged leptons $(e,\mu )$ relevant to the contributions are suggested that may be used as measurements of the evidence of the color-octet components in future $B_c$ experiments. A kind of typical “long-distance contributions” in the annihilation is also estimated.

We derive the equations of time-independent stochastic quantization, without reference to an unphysical fifth time, from the principle of gauge equivalence. It asserts that probability distributions P that give the same expectation values for gauge-invariant observables $〈W〉=\int \mathrm{dAWP}$ are physically indistinguishable. This method escapes the Gribov critique. We derive an exact system of equations that closely resembles the Dyson-Schwinger equations of Faddeev-Popov theory. The system is truncated and solved nonperturbatively, by means of a power law ansatz, for the critical exponents that characterize the asymptotic form at $k\approx 0$ of the gluon propagator in Landau gauge. For the transverse and longitudinal parts, we find, respectively, $D^T\sim {(k}^2{)}^{-1-{\alpha }_T}\approx {(k}^2{)}^{0.043},$ suppressed and in fact vanishing, though weakly, and $D^L\sim {a(k}^2{)}^{-1-{\alpha }_L}\approx {a(k}^2{)}^{-1.521},$ enhanced, with ${\alpha }_T=-2{\alpha }_L.$ Although the longitudinal part vanishes with the gauge parameter a in the Landau-gauge limit $\overrightarrow{a}0$ there are vertices of order $a^{-1}$ so, counterintuitively, the longitudinal part of the gluon propagator does contribute in internal lines in the Landau gauge, replacing the ghost that occurs in Faddeev-Popov theory. We compare our results with the corresponding results in Faddeev-Popov theory.

It has been conjectured that in head-on collisions of neutron stars (NSs), the merged object would not collapse promptly even if the total mass is higher than the maximum stable mass of a cold NS. In this paper, we show that the reverse is true: even if the total mass is less than the maximum stable mass, the merged object can collapse promptly. We demonstrate this for the case of NSs with a realistic equation of state (EOS) (the Lattimer-Swesty EOS) in head-on and near head-on collisions. We propose a “prompt collapse conjecture” for a generic NS EOS for head-on and near head-on collisions.

Higgs bosons from an extended Higgs sector, such as a two-Higgs-doublet model, can have greatly enhanced coupling to the bottom quark. Producing such a Higgs boson in association with a single high-$p_T$ bottom quark via $g\overrightarrow{b}\mathrm{hb}$ allows for the suppression of backgrounds. Previous studies have instead used $gg,q\overline{q}\to b\overline{b}h$ as the production mechanism, which is valid only if both b quarks are at high $p_T.$ We calculate $g\overrightarrow{b}\mathrm{hb}$ at next-to-leading order in QCD, and find that it is an order of magnitude larger than $gg,q\overline{q}\to b\overline{b}h$ at the Fermilab Tevatron and the CERN Large Hadron Collider. This production mechanism improves the prospects for the discovery of a Higgs boson with enhanced coupling to the b quark.

We consider 5 dimensional (5D) $E_6,$ $E_7,$ and $E_8$ supersymmetric grand unified theories (GUTs) on an orbifold $S^1{/Z}_2,$ in which the Higgs fields arise from the fifth components of the 5D gauge fields. We introduce matter fields in 5 dimensions, then the Yukawa interactions are induced from the gauge interactions among the fifth component of gauge fields and the bulk hypermultiplets. The adjoint and fundamental representations of bulk matter fields can induce all Yukawa interactions of the standard model in $E_6$ GUT. Furthermore, realistic fermion mass hierarchies and flavor mixings with the $\mathrm{CP}$ violating phase can be reproduced by introducing the 4D brane localized fields and their interactions. $E_7$ and $E_8$ GUTs can produce all Yukawa interactions by introducing only the adjoint matter hypermultiplet in the bulk. The charge quantization and anomaly-free structure on the 4D wall are satisfactory in our models.

Loop quantum gravity can account for the Bekenstein-Hawking entropy of a black hole provided a free parameter is chosen appropriately. Recently, it was proposed that a new choice of the Immirzi parameter could predict both black hole entropy and the frequencies of quasinormal modes in the large n limit, but at the price of changing the gauge group of the theory. In this Brief Report we use a simple physical argument within loop quantum gravity to arrive at the same value of the parameter. The argument uses strongly the necessity of having fermions satisfying basic symmetry and conservation principles, and therefore supports SU(2) as the relevant gauge group of the theory.

We discuss the breakdown of the perturbative unitarity of noncommutative quantum field theories in an electric-type background in the light of string theory. We consider the analytic structure of string loop two-point functions using a suitable off-shell continuation, and then study the zero slope limit of Seiberg and Witten. In this way we pick up how the unphysical tachyonic branch cut appears in noncommutative field theory. We briefly discuss discontinuities and cutting rules for the full string theory amplitude and relate them to the noncommutative field theoretical results, and also discuss the insight one gains into the magnetic case too.

The dependence of thermal field theory on the surface of quantization and on the velocity of the heat bath is investigated by working in general coordinates that are arbitrary linear combinations of the Minkowski coordinates. In the general coordinates the metric tensor $g_{\overline{\mu \nu }}$ is nondiagonal. The Kubo-Martin-Schwinger condition requires periodicity in thermal correlation functions when the temporal variable changes by an amount $-i/\left(T\sqrt{g_{\overline{00}}}\right).\mathrm{}$ Light-front quantization fails since $g_{\overline{00}}=0;$ however, various related quantizations are possible.

The action for a non-BPS $p=2\mathrm{}$ brane embedded in a flat $N=1,D=4\mathrm{}$ target superspace is obtained through the method of nonlinear realizations of the associated super-Poincaré symmetries. The brane excitation modes correspond to the Nambu-Goldstone degrees of freedom resulting from the broken space translational symmetry and the target space supersymmetries. The action for this $p=2\mathrm{}$ brane is found to be an invariant synthesis of the Akulov-Volkov and Nambu-Goto actions. The dual D2-brane Born-Infeld action is derived. The invariant coupling of matter fields localized on the brane to the Nambu-Goldstone modes is also obtained.

We treat general relativity as an effective field theory, obtaining the full nonanalytic component of the scattering matrix potential to one-loop order. The lowest order vertex rules for the resulting effective field theory are presented and the one-loop diagrams which yield the leading nonrelativistic post-Newtonian and quantum corrections to the gravitational scattering amplitude to second order in G are calculated in detail. The Fourier transformed amplitudes yield a nonrelativistic potential and our result is discussed in relation to previous calculations. The definition of a potential is discussed as well, and we show that the ambiguity of the potential under coordinate changes is resolved.

We study the nature of asymptotic symmetries in topological 3D gravity with torsion. After introducing the concept of an asymptotically anti–de Sitter configuration, we find that the canonical realization of the asymptotic symmetry is characterized by the Virasoro algebra with a classical central charge, the value of which is the same as in general relativity: $c=3\mathrm{}\mathcal{l}/2G.\mathrm{}$

For the theories known as classical sequential growth (CSG) models, it has been conjectured that, up to sets of measure zero, the “stem sets” generate the full σ-algebra of label-invariant measurable sets of causal sets. We prove this for a generic family of CSG models (the “generalized percolation models”). In consequence, we are able not only to identify the “observables” of these theories, but, more importantly, to provide them with an accessible physical interpretation. We suggest that the stem sets will play the same role of fundamental observable in the quantum analog of these theories, i.e. for quantum gravity.

Recent measurements suggest our Universe has a substantial dark energy component, which is usually interpreted in terms of a cosmological constant. Here we examine how much the form of this dark energy can be modified while still retaining an acceptable fit to the high redshift supernova data. We first consider changes in the dark energy equation of state and then explore a model in which the dark energy is interpreted as a fluid with a bulk viscosity.

We consider nontachyonic hybrid inflation in the context of the braneworld cosmology. When one considers models for brane inflation, hybrid inflation is a natural consequence of the tachyon condensation if it appears at the end of inflation. In this case, however, reheating is a difficult problem due to the peculiar properties of the tachyon. In this paper we show some models of brane inflation where a new type of hybrid inflation is realized due to the localized matter fields. The obvious advantage of our scenario is successful reheating, which is due to the potential that is localized on the brane. The serious problem of the loop correction is also avoided.

We present here the general transformation that leaves unchanged the form of the field equations for perfect fluid Friedmann-Robertson-Walker and Bianchi type V cosmologies. The symmetries found can be used as algorithms for generating new cosmological models from existing ones. A particular case of the general transformation is used to illustrate the crucial role played by the number of scalar fields in the occurrence of inflation. Related to this, we also study the existence and stability of Bianchi type V power law solutions.

The pressureless tachyonic matter recently found in superstring field theory has an overabundance problem in cosmology. We argue that this problem can be solved in the brane inflationary scenario if almost all of the tachyon energy is drained (via coupling to the inflaton and matter fields) to heating the Universe, while the rest of the tachyon energy goes to a network of cosmic strings (lower-dimensional BPS D-branes) produced during the tachyon rolling at the end of inflation.

We show explicitly some exciting features of double inflation: (i) it can often lead to strongly correlated adiabatic and entropy (isocurvature) power spectra; (ii) the two-field slow-roll consistency relations can be violated when the correlation is large at the Hubble crossing; (iii) the spectra of adiabatic and entropy perturbations can be strongly scale dependent and tilted toward either the red or blue. These effects are typically due to a light or time-dependent entropy mass and a non-negligible angular velocity in field space during inflation. They are illustrated via a multiparameter numerical search for correlations in two concrete models. The correlation is found to be particularly strong in a supersymmetric scenario due to the rapid growth of entropy perturbations in the tachyonic region separating the two inflationary stages. Our analysis suggests that realistic double-inflation models will provide a rich and fruitful arena for the application of future cosmic data sets and new approximation schemes which go beyond slow roll.

We develop our recent suggestion that inflation may be made past eternal, so that there is no initial cosmological singularity or “beginning of time.” Inflation with multiple vacua generically approaches a steady-state statistical distribution of regions at these vacua, and our model follows directly from making this distribution hold at all times. We find that this corresponds (at the semiclassical level) to particularly simple cosmological boundary conditions on an infinite null surface near which the spacetime looks de Sitter. The model admits an interesting arrow of time that is well defined and consistent for all physical observers that can communicate, even while the statistical description of the entire universe admits a symmetry that includes time reversal. Our model suggests, but does not require, the identification of antipodal points on the manifold. The resulting “elliptic” de Sitter spacetime has interesting classical and quantum properties. The proposal may be generalized to other inflationary potentials, or to boundary conditions that give semieternal but nonsingular cosmologies.

We show how the tree-level unitarity violations of compactified extra dimensional extensions of the standard model become much stronger when the scalar sector is included in the bulk. This effect occurs when the couplings are not suppressed for larger Kaluza-Klein levels, and could have relevant consequences for the phenomenology of the next generation of colliders. We also introduce a simple and generic formalism to obtain unitarity bounds for finite energies, taking into account coupled channels including the towers of Kaluza-Klein excitations.