The s-wave meson-baryon scattering is analyzed for the strangeness $S=-1$ and isospin $I=0\mathrm{}$ sector in a Bethe-Salpeter coupled channel formalism incorporating chiral symmetry. Four channels have been considered: πΣ, $\overline{K}N,$ ηΛ, and $K\Xi .$ The required input to solve the Bethe-Salpeter equation is taken from lowest order chiral perturbation theory in a relativistic formalism. There appear undetermined low energy constants, as a consequence of the renormalization of the amplitudes, which are obtained from fits to the $\pi \overrightarrow{\Sigma }\pi \Sigma$ mass spectrum, to the elastic $\overline{K}\overrightarrow{N}\overline{K}N$ and $\overline{K}\overrightarrow{N}\pi \Sigma$ t matrices and to the $K^{-}\overrightarrow{p}\eta \Lambda$ cross section data. The position and residues of the complex poles in the second Riemann sheet of the scattering amplitude determine the masses, widths, and branching ratios of the $S_{01}$ resonances Λ(1405) and -Λ(1670), in reasonable agreement with experiment. A good overall description of the data, from the πΣ threshold up to 1.75 GeV, is achieved despite the fact that three-body channels have not been explicitly included.

The spin structure of the nucleon is analyzed in the framework of a Lorentz-invariant formulation of baryon chiral perturbation theory. The structure functions of doubly virtual Compton scattering are calculated to one-loop accuracy (fourth order in the chiral expansion). We discuss the generalization of the Gerasimov-Drell-Hearn sum rule, the Burkhardt-Cottingham sum rule and other moments of the nucleon spin structure functions. We give predictions for the forward and the longitudinal-transverse spin polarizabilities of the proton and the neutron at zero and finite photon virtuality. A detailed comparison to results obtained in heavy baryon chiral perturbation theory is also given.

We investigate the production, backgrounds, and signatures of pairs of charged heavy fermions using the $\mathrm{SU}(3{)}_L\otimes \mathrm{U}(1{)}_N$ electroweak model in $e^{+}{e}^{-}$ colliders (Next Linear Collider and CERN Linear Collider). We also analyze the indirect evidence for a boson $Z^{\prime }.$

We construct a realistic theory of grand unification in ${\mathrm{AdS}}_5$ truncated by branes, in which the unified gauge symmetry is broken by boundary conditions and the electroweak scale is generated by the AdS warp factor. We show that the theory preserves the successful gauge coupling unification of the 4D MSSM at the leading-logarithmic level. Kaluza-Klein (KK) towers, including those of the XY gauge and colored Higgs multiplets, appear at the TeV scale, while the extra dimension provides natural mechanisms for doublet-triplet splitting and proton decay suppression. In one possible scenario supersymmetry is strongly broken on the TeV brane, in which case the lightest ${\mathrm{SU}\left(3\right)\mathrm{}}_C\times {\mathrm{SU}\left(2\right)\mathrm{}}_L\times {U\left(1\right)\mathrm{}}_Y$ gauginos are approximately Dirac and the mass of the lightest XY gaugino is pushed well below that of the lowest gauge boson KK mode, improving the prospects for its production at the CERN LHC. The bulk Lagrangian possesses a symmetry that we call GUT parity. If GUT parity is exact, the lightest GUT particle, most likely an XY gaugino, is stable. Once produced in a collider, the XY gaugino hadronizes to form mesons, some of which will be charged and visible as highly ionizing tracks. The lightest supersymmetric particle is the gravitino of mass $\sim {10}^{-3}\mathrm{eV},$ which is also stable if R parity is conserved.

We develop an implementation for a recently proposed noisy Monte Carlo approach to the simulation of lattice QCD with dynamical fermions by incorporating the full fermion determinant directly. Our algorithm uses a quenched gauge field update with a shifted gauge coupling to minimize fluctuations in the trace of the logarithm of the Wilson-Dirac matrix. The details of tuning the gauge coupling shift as well as results for the distribution of noisy estimators in our implementation are given. We present data for some basic observables from the noisy method, as well as the acceptance rate information and discuss potential autocorrelation and sign violation effects. Both the results and the efficiency of the algorithm are compared against those of the hybrid Monte Carlo algorithm.

We describe calculations of $c\overline{c}$ production to next-to-next-to-leading order and next-to-next-to-leading logarithm near threshold in pp and ${\pi }^{-}p$ interactions. We study the relevance of these calculations for existing $c\overline{c}$ total cross section data by examining their sensitivity to partonic threshold kinematics, their convergence properties, and their scale dependence.

Nonperturbative effects in D-meson production in pion-nucleon and proton-nucleon collisions are investigated within the recombination model. The coalescence of perturbatively created charm quarks with sea and valence quarks from projectile and target fragments is shown to be competitive in magnitude with standard fragmentation calculations at both central (small $x_F)$ and forward rapidities. Corresponding flavor asymmetries for inclusive D-meson production are thus mostly generated on the (light-) parton distribution level, and turn out to be in reasonable overall agreement with available fixed-target data. Predictions for upcoming measurements at BNL RHIC are given.

We present a theoretical prediction for the photon spectrum in radiative ${\rm Y}$ decay. Parts of the spectrum have already been understood, but an understanding of the end point region has remained elusive. In this paper we provide the missing piece, and resolve a controversy in the literature. We treat the end point region of $\overrightarrow{{\rm Y}}X\gamma$ decay within the framework of the soft-collinear effective theory (SCET). Within this approach the ${\rm Y}$ structure function arises naturally, and kinematic logarithms are summed by running operators using renormalization group equations. In a previous paper we studied the color-octet contribution to the decay. Here we treat the color-singlet contribution. We combine our result with previous results to obtain the $\overrightarrow{{\rm Y}}X\gamma$ spectrum. We find that resumming the color-singlet contribution in the end point gives a result that is in much better agreement with the data than the leading order prediction.

The density corrections, in terms of the isospin chemical potential ${\mu }_I,$ to the mass of the pions are studied in the framework of the $\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}$ low-energy effective chiral Lagrangian. The pion decay constant $f_{\pi }(T,{\mu }_I)$ is also analyzed. As a function of temperature for ${\mu }_I=0,$ the mass remains quite stable, starting to grow for very high values of T, confirming previous results. However, there are interesting corrections to the mass when both effects (temperature and chemical potential) are simultaneously present. At zero temperature the ${\pi }^{\pm }$ should condensate when ${\mu }_I=\mp m_{\pi }.$ This is no longer valid at finite T. The mass of ${\pi }_0$ acquires also a nontrivial dependence on ${\mu }_I$ due to the finite temperature.

We introduce a parametrization of the effect of unknown corrections from new physics on quark and lepton mass matrices. This parametrization is used in order to study how the hierarchies of quark masses and mixing angles are modified by random perturbations of the Yukawa matrices. We discuss several examples of flavor relations predicted by different textures, analyzing how these relations are influenced by the random perturbations. We also comment on the unlikely possibility that unknown corrections contribute significantly to the hierarchy of masses and mixings.

The relation between leptogenesis and CP violation at low energies is analyzed in detail in the framework of the minimal seesaw mechanism. Working, without loss of generality, in a weak basis where both the charged lepton and the right-handed Majorana mass matrices are diagonal and real, we consider a convenient generic parametrization of the Dirac neutrino Yukawa coupling matrix and identify the necessary condition which has to be satisfied in order to establish a direct link between leptogenesis and CP violation at low energies. In the context of the LMA solution of the solar neutrino problem, we present minimal scenarios which allow for the full determination of the cosmological baryon asymmetry and the strength of CP violation in neutrino oscillations. Some specific realizations of these minimal scenarios are considered. The question of the relative sign between the baryon asymmetry and CP violation at low energies is also discussed.

Neutrino telescopes that measure relative fluxes of ultrahigh-energy ${\nu }_e,{\nu }_{\mu },{\nu }_{\tau }$ can give information about the location and characteristics of sources, about neutrino mixing, and can test for neutrino instability and for departures from CPT invariance in the neutrino sector. We investigate the consequences of neutrino mixing for the neutrino flux arriving at Earth, and consider how terrestrial measurements can characterize distant sources. We contrast mixtures that arise from neutrino oscillations with those signaling neutrino decays. We stress the importance of measuring ${\nu }_e,{\nu }_{\mu },{\nu }_{\tau }$ fluxes in neutrino observatories.

Within the model based on the $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\times \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_R\times \mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_{B-L}$ gauge group and having a bidoublet and two triplets of the Higgs fields (left-right model), the Higgs sector impact on the value of the muon anomalous magnetic moment (AMM) is considered. The contributions coming from the doubly charged Higgs bosons, the singly charged Higgs bosons, and the lightest neutral Higgs boson are taken into account. The obtained value of the muon AMM is a function of the Higgs boson masses and the Higgs boson coupling constants (CC’s). We express the largest part of the CC’s as a function of the heavy neutrino sector parameters. We show that at the particular parameter values the model under study could explain the BNL 2000 result.

The atmospheric muon and neutrino flux have been simulated using the same approach which successfully accounted for the recent secondary proton, electron, and positron flux measurements in orbit by the AMS experiment. For the muon flux, good agreement is obtained with the CAPRICE and HEAT data for altitudes ranging from sea level up to about 38 km. The general features of the calculated atmospheric neutrino flux are reported and discussed. The flux obtained at the Super-Kamiokande experiment location are reported and compared with other calculations. For low neutrino energies the flux obtained is significantly smaller than that used in the data analysis of underground experiment. The simulation results for the SOUDAN experiment site are also reported.

The hyperfine splitting for the $2S$ charmonium state is calculated and the predicted number is ${\Delta }_{\mathrm{HF}}\mathrm{}\left(2S\right)=57\mathrm{}\pm 8\mathrm{MeV},$ being by derivation the lower bound of this splitting. It results in $M\left({\eta }_c\mathrm{}\right(2S\left)\mathrm{}\right)=3630\mathrm{}\pm 8\mathrm{MeV},$ which is smaller by two standard deviations than found in the Belle experiment, but close to the ${\eta }_c\mathrm{}\left(2S\right)\mathrm{}$ mass observed by the same group in the experiment $e^{+}{e}^{-}\to J/\psi {\eta }_c$ where $M\left({\eta }_c\mathrm{}\right(2S\left)\mathrm{}\right)=3622\mathrm{}\pm 12\mathrm{MeV}$ was found.

The T-odd distribution functions contributing to the transversity properties of the nucleon and their role in fueling nontrivial contributions to azimuthal asymmetries in semi-inclusive deep inelastic scattering are investigated. We use a dynamical model to evaluate these quantities in terms of HERMES kinematics.

Recent results on zero modes of the Abelian Dirac operator in three dimensions support to some degree the conjecture that the Chern-Simons action admits only certain quantized values for gauge fields that lead to zero modes of the corresponding Dirac operator. Here we show that this conjecture is wrong by constructing an explicit counterexample.

We derive an approximate renormalization group (RG) solution for the linear sigma model of Gell-Mann and Levy at finite temperature. For our purposes, the Fermionic degrees of freedom of the model are interpreted as quarks which interact via the $\sigma$ and $\pi$ mesons to provide a phenomenological description of hot nuclear matter at temperatures from 1 GeV to approximately 100 MeV. Our solution consists of two coupled, nonlinear flow equations for the Yukawa coupling, g, of the model and the Bosonic effective potential, U. These equations are solved numerically to study the behavior of the model as it evolves from high to low energy scales at finite temperature T. This allows us to determine the critical temperature, $T_c,$ at which chiral symmetry breaking occurs, and to assess the relative sensitivity of this quantity with respect to variations in the input parameters of the model. Our results are consistent with values for $T_c$ obtained from other theoretical approaches such as lattice gauge theory or other RG techniques.

The color superconductivity under flavor asymmetric conditions relevant to compact star phenomenology is studied within the Nambu–Jona-Lasinio model. We focus on the effect of the deformation of the Fermi surfaces on the pairing properties and the energy budget of the superconducting state. We find that at finite flavor asymmetries the color superconducting BCS state is unstable towards spontaneous quadrupole deformation of the Fermi surfaces of the d and u quarks into ellipsoidal form. The ground state of the phase with deformed Fermi surfaces corresponds to a superposition of prolate and oblate deformed Fermi ellipsoids of d and u quarks.