The muon transverse polarization in the $K^{+}\to {\mu }^{+}\nu \gamma$ process induced by the electromagnetic final state interaction is calculated in the framework of the standard model. It is shown that one loop contributions lead to a nonvanishing muon transverse polarization. The value of the muon transverse polarization averaged over the kinematical region of $E_{\gamma }>~20\hspace{0.5em}\mathrm{MeV}$ is equal to $5.63\times {10}^{-4}.$

We have searched for neutron-antineutron oscillations using the 5.56 fiducial kiloton-year exposure of the Soudan 2 iron tracking calorimeter. We require candidate $n\mathrm{n̄}$ occurrences to have $>~4$ prongs (tracks and showers) and to have kinematics compatible with $\mathrm{n̄}N$ annihilation within a nucleus. We observe five candidate events, with an estimated background from atmospheric neutrino and cosmic ray induced events of $4.5\pm 1.2$ events. Previous experiments with smaller exposures observed no candidates, with estimated background rates similar to this experiment. We set a lifetime lower limit at 90% C.L. for the $n\mathrm{n̄}$ oscillation time in iron: $T_A\left(\mathrm{Fe}\right)>\mathrm{}7.2\mathrm{}\times {10}^{31}\hspace{0.5em}\mathrm{yr}.$ The corresponding lower limit for oscillation of free neutrons is ${\tau }_{n\mathrm{n̄}}>1.3\mathrm{}\times {10}^8\hspace{0.5em}\sec .$

We present a measurement of time-dependent CP-violating asymmetries in neutral B meson decays collected with the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at the Stanford Linear Accelerator Center. The data sample consists of 29.7 ${\mathrm{fb}}^{\mathrm{-}1}$ recorded at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance and 3.9 ${\mathrm{fb}}^{\mathrm{-}1}$ off resonance. One of the neutral B mesons, which are produced in pairs at the ${\rm Y}\mathrm{}\left(4S\right),$ is fully reconstructed in the CP decay modes $J/\psi K_S^0,$ $\psi {\mathrm{}\left(2S\right)K}_S^0,$ ${\chi }_{c1\mathrm{}}{K}_S^0,$ $J/\psi K^{*0}$ ${(K}^{*0}\to K_S^0{\pi }^0)$ and $J/\psi K_L^0,$ or in flavor-eigenstate modes involving $D^{\left(*\right)}\pi /\rho {/a}_1$ and $J/\psi K^{*0}$ ${(K}^{*0}\to K^{+}{\pi }^{-}).\mathrm{}$ The flavor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identified leptons and kaons. A neural network tagging algorithm is used to recover events without a clear lepton or kaon tag. The proper time elapsed between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities, the time-difference resolution function, and the $B^0-B^0$ oscillation frequency $\Delta m_d$ are measured with a sample of about 6350 fully-reconstructed $B^0$ decays in hadronic flavor-eigenstate modes. A maximum-likelihood fit to this flavor eigenstate sample finds $\Delta m_d=0.516\mathrm{}\pm 0.016\left(\mathrm{stat}\right)\pm 0.010\left(\mathrm{syst}\right){\mathrm{ps}}^{-1}.$ The value of the asymmetry amplitude $\sin 2\beta$ is determined from a simultaneous maximum-likelihood fit to the time-difference distribution of the flavor-eigenstate sample and about 642 tagged $B^0$ decays in the CP-eigenstate modes. We find $\sin 2\beta =0.59\mathrm{}\pm 0.14\left(\mathrm{stat}\right)\pm 0.05\left(\mathrm{syst}\right),$ demonstrating that CP violation exists in the neutral B meson system. We also determine the value of the CP violation parameter $|\lambda |=0.93\mathrm{}\pm 0.09\left(\mathrm{stat}\right)\pm 0.03\left(\mathrm{syst}\right),$ which is consistent with the expectation of $|\lambda |=1\mathrm{}$ for no direct CP violation.

A cosmological model with pressureless matter and a fluid of negative pressure is studied. At the perturbative level, fluctuations of both fluids are considered. It is shown that, at least at very large scales, the fluid of negative pressure, which represents the dark energy content of the universe, clusters like the dust fluid. Numerical integration reveals that this behavior may also occur at scales smaller than the Hubble radius.

We present a new scenario for baryon number violation that may take place in models with large extra dimensions. Our idea is interesting because leptogenesis with a low reheating temperature requires an alternative source of $B+L$ violation to convert the produced leptons into baryons. If one considers a model with an intermediate compactification radius, the reheating temperature may be allowed to become higher than the critical temperature of the conventional electroweak phase transition. Our mechanism is still important in this case, because it provides the phase boundary, which is an essential ingredient of electroweak baryogenesis.

We describe topological vortices of a scalar field minimally coupled to a fermionic field. We derive exact solutions for large values of the Ginzburg-Landau parameter, investigate the dynamics of weakly curved vortex loops, and establish a possibility of the formation of classically stable vortex rings.

We discuss the problem of the motion of classical strings in some black hole and cosmological spacetimes. In particular, the null string limit (zero tension) of tensile strings is considered. We present some new exact string solutions in a Reissner-Nordström black hole background as well as in the Einstein static universe and in the Einstein-Schwarzschild (a black hole in the Einstein static universe) spacetime. These solutions can give some insight into the general nature of the propagation of strings (cosmic and fundamental) in curved backgrounds.

We consider the scenario emerging from the dynamics of a generalized Born-Infeld theory. The equation of state describing this system is given in terms of the energy density $\rho$ and pressure p by the relationship $p=-A/{\rho }^{\alpha },$ where A is a positive constant and $0<\mathrm{}\alpha <~1.$ We discuss the conditions under which homogeneity arises and show that this equation of state describes the evolution of a universe evolving from a phase dominated by nonrelativistic matter to a phase dominated by a cosmological constant via an intermediate period where the effective equation of state is given by $p=\alpha \rho .$

The possibility of a friction term $\eta \dot{\phi }$ in the equation of motion for a scalar field is investigated in nonequilibrium field theory. The central result is that this equation of motion does not possess a time-derivative expansion, and so the friction coefficient $\eta$ is not well defined. It is nevertheless possible to obtain an effective friction coefficient numerically. In $\lambda {\Phi }^4$ theory, this differs greatly from existing estimates based on linear response theory, and is actually negative for some values of temperature and coupling constant, indicating that the breakdown of the time-derivative expansion may be quantitatively rather significant.

Monte Carlo simulations are performed in a five-dimensional lattice $\mathrm{SU}\left(2\right)\mathrm{}$ Yang-Mills theory with a compactified extra dimension, and scaling laws are studied. Our simulations indicate that, as the compactification radius R decreases, the confining phase spreads more and more to the weak coupling regime, and the effective dimension of the theory changes gradually from five to four. Our simulations also indicate that the limit $a_4\to 0$ with ${R/a}_4$ kept fixed exists in both the confining and deconfining phases if ${R/a}_4$ is small enough, where $a_4$ is the lattice spacing in the four-dimensional direction. We argue that there exists a maximal radius above which the color degrees of freedom are not confined. Comments on deconstructing extra dimensions are given.

The reasons for using low-lying Dirac eigenmodes to probe the local structure of topological charge fluctuations in QCD are discussed, and it is pointed out that the qualitative double-peaked behavior of the local chiral orientation probability distribution in these modes is necessary, but not sufficient, for dominance of instantonlike fluctuations. The results with the overlap Dirac operator in Wilson gauge backgrounds at lattice spacings ranging from $a\approx 0.04\mathrm{fm}$ to $a\approx 0.12\mathrm{fm}$ are reported, and it is found that the size and density of local structures responsible for double peaking of the distribution are in disagreement with the assumptions of the instanton liquid model. More generally, our results suggest that vacuum fluctuations of topological charge are not effectively dominated by locally quantized (integer-valued) lumps in QCD.

We study $\overrightarrow{Z}{l}^{+}{l}^{-}$ and $\overrightarrow{W}{\nu }_l{l}^{+}$ decays in the standard model including noncommutative effects. We observe that these effects appear in the flavor-dependent part of the decay widths of the processes under consideration and, therefore, they are more effective for the heavy lepton decays.

Previous work on high-density QCD suggests that the ground state configuration in the presence of a nonzero neutrino chemical potential consists of color-flavor locked matter plus a homogeneous condensate of neutral and positive kaons. We consider here the stability of this homogeneous configuration toward the production of a charge-separated mixed phase, and find that the system is indeed stable against the production of such a heterogenous configuration. We identify the critical value of the fine structure constant which would allow for phase separation. We also derive dispersion relations for the low-lying excitations above the kaon-condensed ground state and discuss their possible phenomenological implications.

In a recent paper, we presented a calculation of the $\mathcal{O}\left({\alpha }_s\right)$ virtual corrections to $\overrightarrow{b}{\mathrm{sl}}^{+}{l}^{-}$ and of those bremsstrahlung terms that are needed to cancel the infrared divergences. In the present paper we work out the remaining $\mathcal{O}\left({\alpha }_s\right)$ bremsstrahlung corrections to $\overrightarrow{b}{\mathrm{sl}}^{+}{l}^{-},$ which do not suffer from infrared and collinear singularities. These new contributions turn out to be small numerically. In addition, we also investigate the impact of the definition of $m_c$ on the numerical results.

We present a detailed analysis of the muonic analogue of neutrinoless double beta decay $({\mu }^{-},{\mu }^{+})$ conversion. We study several lepton number violating (LNV) mechanisms potentially triggering this process: exchange by light and heavy Majorana neutrinos as well as exchange by supersymmetric particles participating in R-parity violating interactions. The nuclear structure is taken into account within the renormalized quasiparticle random phase approximation method. This is the first realistic treatment of nuclear structure aspects of the $({\mu }^{-},{\mu }^{+})$ conversion. We estimate the rate of this process utilizing the existing experimental constraints on the parameters of the underlying LNV interactions and conclude that the $({\mu }^{-},{\mu }^{+})$ conversion will hardly be detectable in the near future experiments.

We construct a gravitational-anomaly-free effective action for the coupled system of type-IIA $D=10\mathrm{}$ dynamical supergravity interacting with a NS5-brane. The NS5-brane is considered as elementary in that the associated current is a $\delta$ function supported on its world volume. Our approach is based on a Chern kernel which encodes the singularities of the three-form field strength near the brane in an SO(4)-invariant way and provides a solution for its Bianchi identity in terms of a two-form potential. A dimensional reduction of the recently constructed anomaly-free effective action for an elementary M5-brane in $D=11\mathrm{}$ is seen to reproduce our ten-dimensional action. The Chern-kernel approach provides in particular a concrete realization of the anomaly cancellation mechanism envisaged by Witten.

A no-scale supersymmetry (SUSY) breaking model is investigated in the minimal extension of the minimal supersymmetric standard model (MSSM) with a gauged $\mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_{B-L}$ symmetry. We specifically consider a unification-inspired model with the gauge groups $\mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}_C\times \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\times \mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_Y\times \mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_{B-L}\subset \mathrm{SU}\mathrm{}\left(5\right)\mathrm{}\times \mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_5$ for illustration. While the no-scale boundary condition at the grand unification scale ${(M}_G\simeq 2\times {10}^{16}\hspace{0.5em}\mathrm{GeV})$ in the MSSM is not consistent with phenomenological constraints, we show that it is if the gaugino of the $\mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_5$ multiplet is several times heavier than the gauginos of the MSSM. However, if $\mathrm{SU}\mathrm{}\left(5\right)\mathrm{}\times \mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_5$ is further embedded in a larger simple group, e.g., SO(10), the no-scale boundary condition at $M_G$ is inconsistent with phenomenological constraints. If we relax the no-scale boundary condition and allow nonzero soft scalar masses for the Higgs fields which spontaneously break the $\mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_5$ symmetry, the resultant spectrum of SUSY particles becomes consistent with all the phenomenological constraints, even if we impose the GUT relation on the gauge coupling and the gaugino mass of the $\mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_5.$ In this case, the SUSY $\mathrm{CP}$ problem is also solved, since the condition $B\mu =0\mathrm{}$ at the boundary can be imposed consistently with electroweak symmetry breaking.

We study lepton flavor violation (LFV) in tau decays induced by heavy Majorana neutrinos within two models: (I) the standard model with additional right-handed heavy Majorana neutrinos, i.e., a typical seesaw-type model; (II) the standard model with left-handed and right-handed neutral singlets, which are inspired by certain scenarios of $\mathrm{SO}\left(10\right)\mathrm{}$ models and heterotic superstring models with $E_6$ symmetry. We calculate various LFV branching ratios and a T-odd asymmetry. The seesaw model I predicts very small branching ratios for LFV processes in most of the parameter space, although in a very restricted parameter region it can reach maximal branching ratios $Br\left(\overrightarrow{\tau }\mu \gamma \right)\sim {10}^{-9}$ and $Br\left(\overrightarrow{\tau }3\mu \right)\sim {10}^{-10}.$ In contrast, model II may show branching ratios $Br\left(\overrightarrow{\tau }e\gamma \right)\sim {10}^{-8}$ and $Br\left(\overrightarrow{\tau }3e\right)\lesssim {10}^{-9}$ over a sizable region of the parameter space, large enough to be tested by experiments in the near future.

We investigate the radiation amplitude zeros exhibited by many standard model amplitudes for triple weak gauge boson production processes. We show that $\mathrm{WZ}\gamma$ production amplitudes have an especially rich structure in terms of zeros; these amplitudes have zeros originating from several different sources. It is also shown that the type-I current null zone is the special case of the equality of the specific helicity amplitudes.

The latest electroweak precision data allow the existence of additional chiral generations in the standard model. We study the influence of extra generations on the production of the standard model Higgs boson at hadron colliders. Because of the enhancement of the gluon fusion channel, the “golden mode” becomes more promising even at the upgraded Fermilab Tevatron. Furthermore, the formation of the fourth family quarkonia with the subsequent $\overrightarrow{\eta }\mathrm{Zh}$ decay introduces an additional tool for investigation of Higgs boson properties.