We study the pion-nucleon sigma term in vacuum and in nuclear matter in the framework of global color model of QCD. With the effective gluon propagator being taken as the $\delta$-function in momentum space of Munczek-Nomirovsky model, we estimate that the sigma term at chiral limit in the vacuum is $9/2$ times the current quark mass and it decreases with the nuclear matter density. With the presently obtained in-medium pion-nucleon sigma term, we study the in-medium chiral quark condensate and obtain a reasonable variation behavior against the nuclear matter density.

We present results for the strong widths corresponding to the ${\Sigma }_c\to {\Lambda }_c\pi$, ${\Sigma }_c^{*}\to {\Lambda }_c\pi$ and ${\Xi }_c^{*}\to {\Xi }_c\pi$ decays. The calculations have been done in a nonrelativistic constituent quark model with wave functions that take advantage of the constraints imposed by heavy quark symmetry. Partial conservation of axial current hypothesis allows us to determine the strong vertices from an analysis of the axial current matrix elements. Our results $\Gamma ({\Sigma }_c^{++}\to {\Lambda }_c^{+}{\pi }^{+})=2.41\pm 0.07\pm 0.02\mathrm{MeV}$, $\Gamma ({\Sigma }_c^{+}\to {\Lambda }_c^{+}{\pi }^0)=2.79\pm 0.08\pm 0.02\mathrm{MeV}$, $\Gamma ({\Sigma }_c^0\to {\Lambda }_c^{+}{\pi }^{-})=2.37\pm 0.07\pm 0.02\mathrm{MeV}$, $\Gamma ({\Sigma }_c^{*++}\to {\Lambda }_c^{+}{\pi }^{+})=17.52\pm 0.74\pm 0.12\mathrm{MeV}$, $\Gamma ({\Sigma }_c^{*+}\to {\Lambda }_c^{+}{\pi }^0)=17.31\pm 0.73\pm 0.12\mathrm{MeV}$, $\Gamma ({\Sigma }_c^{*0}\to {\Lambda }_c^{+}{\pi }^{-})=16.90\pm 0.71\pm 0.12\mathrm{MeV}$, $\Gamma ({\Xi }_c^{*+}\to {\Xi }_c^0{\pi }^{+}+{\Xi }_c^{+}{\pi }^0)=3.18\pm 0.10\pm 0.01\mathrm{MeV}$, and $\Gamma ({\Xi }_c^{*0}\to {\Xi }_c^{+}{\pi }^{-}+{\Xi }_c^0{\pi }^0)=3.03\pm 0.10\pm 0.01\mathrm{MeV}$ are in good agreement with experimental determinations.

We derive a new factorization relation for the semileptonic radiative decay $B\to \pi \ell \nu \gamma$ in the kinematical region of a slow pion $|{\overrightarrow{p}}_{\pi }|\sim \Lambda$ and an energetic photon $E_{\gamma }\gg \Lambda$, working at leading order in $\Lambda /m_b$. In the limit of a soft pion, the nonperturbative matrix element appearing in this relation can be computed using chiral perturbation theory. We present a phenomenological study of this decay, which may be important for a precise determination of the exclusive nonradiative decay.

We study braneworlds in a five-dimensional bulk, where cosmological expansion is mimicked by motion through ${\mathrm{AdS}}_5$. We show that the five-dimensional graviton reduces to the four-dimensional one in the late time approximation of such braneworlds. Inserting a fixed regulator brane far from the physical brane, we investigate quantum graviton production due to the motion of the brane. We show that the massive Kaluza-Klein modes decouple completely from the massless mode and they are not generated at all in the limit where the regulator brane position goes to infinity. In the low energy limit, the massless four-dimensional graviton obeys the usual 4D equation and is therefore also not generated in a radiation-dominated universe.

Charged stars have the potential of becoming charged black holes or even naked singularities. We present a set of numerical solutions of the Tolman-Oppenheimer-Volkov equations that represents spherical charged compact stars in hydrostatic equilibrium. The stellar models obtained are evolved forward in time integrating the Einstein-Maxwell field equations. We assume an equation of state of a neutron gas at zero temperature. The charge distribution is taken as being proportional to the rest mass density distribution. The set of solutions present an unstable branch, even with charge-to-mass ratios arbitrarily close to the extremum case. We perform a direct check of the stability of the solutions under strong perturbations and for different values of the charge-to-mass ratio. The stars that are in the stable branch oscillate and do not collapse, while models in the unstable branch collapse directly to form black holes. Stars with a charge greater than or equal to the extreme value explode. When a charged star is suddenly discharged, it does not necessarily collapse to form a black hole. A nonlinear effect that gives rise to the formation of a shell of matter (in supermassive stars), is negligible in the present simulations. The results are in agreement with the third law of black hole thermodynamics and with the cosmic censorship conjecture.

We study the spectrum of metric fluctuation in $\kappa$-deformed inflationary universe. We write the theory of scalar metric fluctuations in the $\kappa$-deformed Robertson-Walker space, which is represented as a nonlocal theory in the conventional Robertson-Walker space. One important consequence of the deformation is that the mode generation time is naturally determined by the structure of the $\kappa$-deformation. We expand the nonlocal action in $H^2/{\kappa }^2$, with $H$ being the Hubble parameter and $\kappa$ the deformation parameter, and then compute the power spectra of scalar metric fluctuations both for the cases of exponential and power law inflations up to the first order in $H^2/{\kappa }^2$. We show that the power spectra of the metric fluctuation have nontrivial corrections on the time dependence and on the momentum dependence compared to the commutative space results. Especially for the power law inflation case, the power spectrum for UV modes is weakly blueshifted early in the inflation and its strength decreases in time. The power spectrum of far-IR modes has cutoff proportional to $k^3$ which may explain the low cosmic microwave background (CMB) quadrupole moment.

A new scenario of baryogenesis is presented, within the split fermions framework. Our model employs a first order phase transition of the localizer field. The standard model (SM), Kobayashi-Maskawa phase induces a sizable $CP$ asymmetry. The usual suppression of $CP$ violation which arises in the SM baryogenesis is absent due to the existence of order one Yukawa couplings before the fermions are localized in the extra dimension. Models of the above type naturally contain $B-L$ violating operators, allowed by the SM symmetries, which induce the baryon asymmetry. Our mechanism demonstrates the following concept: the flavor puzzle and the SM failure to create the baryon asymmetry are linked and may have a common resolution which does not rely on introduction of new $CP$ violating sources.

Motivated by the interpretation of the recent results on the TeV gamma radiation from the galactic center, including the new 2004 HESS data, as a by-product of dark matter particles annihilations, we address the question of the largest possible neutralino masses and pair-annihilation cross sections in supersymmetric models. Extending the parameter space of minimal models, such as the mSUGRA and the mAMSB scenarios, to general soft supersymmetry (SUSY) breaking Higgs masses gives access to the largest possible pair annihilation rates, corresponding to resonantly annihilating neutralinos with maximal gaugino-Higgsino mixing. Adopting a model-independent approach, we provide analytical and numerical upper limits for the neutralino pair annihilation cross section. A possible loophole is given by the occurrence of nonperturbative electroweak resonances, a case we also consider here. We then show that a thorough inclusion of QCD effects in gluino (co-)annihilations can, in extreme scenarios, make neutralinos with masses in the hundreds of TeV range, well beyond the $s$-wave unitarity bound, viable dark matter candidates. Finally, we outline the ranges of neutralino masses and cross sections for models thermally producing a WMAP relic abundance, thus providing reference values for “best case” indirect SUSY dark matter detection rates.

We consider the impact of second order corrections to the geodesic equation governing gravitational lensing. We start from the full second order metric, including scalar, vector, and tensor perturbations, and retain all relevant contributions to the cosmic shear corrections that are second order in the gravitational potential. The relevant terms are: the nonlinear evolution of the scalar gravitational potential, the Born correction, and lens-lens coupling. No other second order terms contribute appreciably to the lensing signal. Since ray-tracing algorithms currently include these three effects, this derivation serves as rigorous justification for the numerical predictions.

We contrast the experimental signatures of low-energy supersymmetry and the model of Universal Extra Dimensions and discuss various methods for their discrimination at hadron colliders. We study the discovery reach of the Tevatron and the LHC for level 2 Kaluza-Klein modes, which would indicate the presence of extra dimensions. We find that with $100{\mathrm{fb}}^{-1}$ of data the LHC will be able to discover the ${\gamma }_2$ and $Z_2$ KK modes as separate resonances if their masses are below 2 TeV. We also investigate the possibility to differentiate the spins of the superpartners and KK modes by means of the asymmetry method of Barr.

The possible analytic extensions of Matsubara thermal $n$-point functions from discrete, imaginary energies to more general complex energies are investigated. It is known that for $n\ge 4$ most of the analytic extensions cannot be expressed as linear combinations of the usual $2^n$ different real-time $n$-point functions. For the case $n=4$ the explicit products of real-time field operators are found whose Fourier transforms can be extended analytically to certain domains of complex energy.

The phases in a generic low-energy supersymmetric model are severely constrained by the experimental upper bounds on the electric dipole moments of the electron and the neutron. Coupled with the requirement of radiative electroweak symmetry breaking, this results in a large degree of fine-tuning of the phase parameters at the unification scale. In supergravity type models, this corresponds to very highly tuned values for the phases of the bilinear Higgs coupling parameter $B$ and the universal trilinear coupling $A_0$. We identify a cancellation/enhancement mechanism associated with the renormalization group evolution of $B$, which, in turn, reduces such fine-tuning quite appreciably without taking recourse to very large masses for the supersymmetric partners. We find a significant amount of reduction of this fine-tuning in nonuniversal gaugino mass models that do not introduce any new phases.

We study quantum electrodynamics in a ($2+1$)-dimensional space-time with two flavors of dynamical fermions by numerical simulations on the lattice. We discretize the theory using both the compact and the noncompact formulations and analyze the behavior of the chiral condensate and of the monopole density in the finite lattice regime as well as in the continuum limit. By comparing the results obtained with the two approaches, we draw some conclusions about the possible equivalence of the two lattice formulations in the continuum limit.

Impact parameter dependent parton distributions are transversely distorted when one considers transversely polarized nucleons and/or quarks. This provides a physical mechanism for the $T$-odd Sivers effect in semi-inclusive deep-inelastic scattering. The transverse distortion can also be connected with Ji’s quark angular momentum relation. The distortion of chirally odd impact parameter dependent parton distributions is related to chirally odd generalized parton distributions (GPDs). This result is used to provide a decomposition of the quark angular momentum with respect to (w.r.t.) quarks of definite transversity. Chirally odd GPDs can thus be used to determine the correlation between quark spin and quark angular momentum in unpolarized nucleons. Based on the transverse distortion, we also suggest a qualitative connection between chirally odd GPDs and the Boer-Mulders effect.

We obtain relations among boundary states in bosonic minimal open string theory using the boundary ground ring. We also obtain a difference equation that boundary correlators must satisfy.

A recursive algebraic method which allows one to obtain the Feynman or Schwinger parametric representation of a generic $L$-loops and $(E+1)$ external lines diagram, in a scalar ${\varphi }^3\oplus {\varphi }^4$ theory, is presented. The representation is obtained starting from an initial parameters matrix, which relates the scalar products between internal and external momenta, and which appears directly when this parametrization is applied to the momentum space representation of the graph. The final product is an algebraic formula that shows explicitly the external momenta dependence and also an algorithm that can be easily programmed, either in a computer programming language (C/C++, Fortran, …) or in a symbolic calculation package (Maple, Mathematica, …).

We perform the nonlinear realization or the coset formulation of the pure $\mathcal{N}=4$, $D=5$ supergravity. We derive the Lie superalgebra which parameterizes a coset map whose induced Cartan-Maurer form produces the bosonic field equations of the pure $\mathcal{N}=4$, $D=5$ supergravity by canonically satisfying the Cartan-Maurer equation. We also obtain the first-order field equations of the theory as a twisted self-duality condition for the Cartan-Maurer form within the geometrical framework of the coset construction.

Lovelock gravity is an important extension of general relativity that provides a promising framework to study curvature corrections to the Einstein action, while avoiding ghosts and keeping second order field equations. This paper derives the greybody factors for $D$-dimensional black holes arising in a theory with a Gauss-Bonnet curvature-squared term. These factors describe the nontrivial coupling between black holes and quantum fields during the evaporation process: they can be used both from a theoretical viewpoint to investigate the intricate space-time structure around such a black hole, and for phenomenological purposes in the framework of braneworld models with a low Planck scale. We derive exact spectra for the emission of scalar, fermion and gauge fields emitted on the brane, and for scalar fields emitted in the bulk, and demonstrate how the Gauss-Bonnet term can change the bulk-to-brane emission rates ratio in favor of the bulk channel in particular frequency regimes.

We present a perturbative reconstruction method to make a skymap of gravitational-wave backgrounds (GWBs) observed via space-based interferometer. In the presence of anisotropies in GWBs, the cross-correlated signals of observed GWBs are inherently time dependent due to the nonstationarity of the gravitational-wave detector. Since the cross-correlated signal is obtained through an all-sky integral of primary signals convolving with the antenna pattern function of gravitational-wave detectors, the nonstationarity of cross-correlated signals, together with full knowledge of antenna pattern functions, can be used to reconstruct an intensity map of the GWBs. Here, we give two simple methods to reconstruct a skymap of GWBs based on the perturbative expansion in low-frequency regime. The first one is based on harmonic-Fourier representation of data streams and the second is based on “direct” time-series data. The latter method enables us to create a skymap in a direct manner. The reconstruction technique is demonstrated for the case of the Galactic gravitational-wave background observed via planned space interferometer, LISA. Although the angular resolution of low-frequency skymap is rather restricted, the methodology presented here would be helpful in discriminating the GWBs of galactic origins by those of the extragalactic and/or cosmological origins.