We examine the effects of R-parity violating (RPV) supersymmetry on the two-photon B decays $\overrightarrow{B}{X}_s\gamma \gamma$ and $B_s\to \gamma \gamma .$ We find that, although there are many one-loop RPV diagrams, which can contribute to these two-photon B decays, the RPV effect is dominated by a single diagram. This diagram, named here $\lambda$-irreducible, has a distinct topology, which is irrelevant for the $\overrightarrow{b}s\gamma$ amplitude at one-loop, and has thus a negligible effect on the one-photon decay $\overrightarrow{B}{X}_s\gamma .$ We show that the $\lambda$-irreducible RPV diagram can give ${BR(B}_s\to \gamma \gamma )\sim 5\times {10}^{-6}$ and $BR\left(\overrightarrow{B}{X}_s\gamma \gamma \right)\sim 6\times {10}^{-7},$ which is about 16 and 5 times larger than the SM values, respectively. Although the enhancement to the decay width of $\overrightarrow{B}{X}_s\gamma \gamma$ is not that dramatic, we find that the energy distribution of the two photons is appreciably different from the SM, due to new threshold effects caused by the distinct topology of the RPV $\lambda$-irreducible diagram. Moreover, this diagram significantly changes the forward-backward asymmetry with respect to the softer photon in $\overrightarrow{B}{X}_s\gamma \gamma .$ Thus, the RPV effect in $\overrightarrow{B}{X}_s\gamma \gamma$ can be discerned using these observables.

We discuss in detail the symmetry breaking and related issues in the minimal renormalizable supersymmetric grand unified theory. We find all the possible patterns of symmetry breaking, compute the associated particle spectrum and study its impact on the physical scales of the theory. In particular, the complete mass matrices of the $\mathrm{SU}\left(2\right)\mathrm{}$ doublets and the color triplets are computed in connection with the doublet-triplet splitting and the $d=5\mathrm{}$ proton decay. We explicitly construct the two light Higgs doublets as a function of the Higgs superpotential parameters. This provides a framework for the analysis of phenomenological implications of the theory, to be carried out in a second paper.

The semiclassical quantization of the chiral soliton model is studied for an arbitrary number of colors and flavors. The quantum numbers of the baryons in the soliton model are derived and are shown to agree with those in the constituent quark model for normal as well as exotic baryons. The general analysis elucidates the correct definition of exoticness for the three-flavor case, and allows one to interpret the soliton state in terms of quark model variables. The quantum numbers of all the allowed soliton states for the physically relevant case of three flavors are derived.

A sizable rate of events, with several pairs of heavy quarks produced contemporarily by multiple parton interactions, may be expected at very high energies as a consequence of the large parton luminosities. The production rates are enhanced in hadron-nucleus reactions, which may represent a convenient tool to study the phenomenon. We compare the different contributions to $b\overline{b}b\overline{b},$ $c\overline{c}c\overline{c},$ and $b\overline{b}c\overline{c}$ production due to single- and double-parton scatterings, in collisions of protons with nuclei at the CERN LHC.

Using a bound-state model of weakly bound gluons for glueballs made of two gluons and a natural generalization of the perturbative QCD formalism for exclusive hadronic processes, we present results for glueball production in radiative $J/\psi ,{\rm Y}$ decays into several possible glueball states, including $L\ne 0$ ones. We perform a detailed phenomenological analysis, presenting results for the more favored experimental candidates and for decay angular distributions.

We study the robustness of the determination of the neutrino masses and mixing from the analysis of atmospheric and K2K data under the presence of different forms of phenomenologically allowed new physics in the ${\nu }_{\mu }–{\nu }_{\tau }$ sector. We focus on vector and tensor-like new physics interactions which allow us to treat, in a model independent way, effects due to the violation of the equivalence principle, violations of the Lorentz invariance both CPT conserving and CPT violating, non-universal couplings to a torsion field and non-standard neutrino interactions with matter. We perform a global analysis of the full atmospheric data from SKI together with long baseline K2K data in the presence of ${\nu }_{\mu }\to {\nu }_{\tau }$ transitions driven by neutrino masses and mixing together with sub-dominant effects due to these forms of new physics. We show that within the present degree of experimental precision, the extracted values of masses and mixing are robust under those effects and we derive the upper bounds on the possible strength of these new interactions in the ${\nu }_{\mu }–{\nu }_{\tau }$ sector.

We discuss the consequences of the chiral doubling scenario for baryons built of heavy and light quarks. In particular, we use the soliton description for baryons, demonstrating why each heavy-light baryon should be accompanied by the opposite parity partner. Our argumentation holds both for ordinary baryons and for exotic heavy pentaquarks which are required by the symmetries of QCD to appear in parity doublets, separated by the mass shift of the chiral origin. Interpreting the recently observed by BaBaR, CLEO, and Belle Collaborations charmed mesons with assignment ${(0\mathrm{}}^{+}{,1\mathrm{}}^{+})$ as the parity partners of known D and $D^{*}$ mesons, allows us to estimate the parameters of the mesonic effective Lagrangian, and in consequence, estimate the masses of ground states and excited states of both parities. In particular, we interpret the state recently reported by the H1 experiment at HERA as a parity partner ${\tilde{\Theta }}_c^0\mathrm{}\left(3099\right)\mathrm{}$ of yet undiscovered ground-state pentaquark ${\Theta }_c^0\mathrm{}\left(2700\right).$

One starts from a planar Maxwell-Chern-Simons model endowed with a Lorentz-violating term. The Dirac sector is introduced exhibiting a Yukawa and a minimal coupling with the scalar and the gauge fields, respectively. One then evaluates the electron-electron interaction as the Fourier transform of the Möller scattering amplitude carried out in the nonrelativistic limit. In the case of a purely timelike background, the interaction potential can be exactly solved, exhibiting a typical massless behavior far from the origin. The scalar interaction potential is always attractive whereas the gauge intermediation may also present attraction even when considered in the presence of the centrifugal barrier and the $A^2$ term. Such a result is a strong indication that electron-electron bound states may appear in this theoretical framework.

We investigate SUSY breaking mediated through the deformation of the space-time geometry due to the backreaction of a nontrivial configuration of a bulk scalar field. To illustrate its features, we work with a toy model in which the bulk is four dimensions. Using the superconformal formulation of SUGRA, we provide a systematic method of deriving the 3D effective action expressed by the superfields, which can basically be extended to 5D SUGRA straightforwardly.

Within an effective field theory framework we compute the most general structure of the one-loop corrections to the 4D gauge couplings in one- and two-dimensional orbifold compactifications with nonvanishing constant gauge background (Wilson lines). Although such models are nonrenormalizable, we keep the analysis general by considering the one-loop corrections in three regularization schemes: dimensional regularization (DR), zeta-function regularization (ZR), and proper-time cutoff regularization (PT). The relations among the results obtained in these schemes are carefully addressed. With minimal redefinitions of the parameters involved, the results obtained for the radiative corrections can be applied to most orbifold compactifications with one or two compact dimensions. The link with string theory is discussed. We mention a possible implication for the gauge coupling unification in such models.

We discuss the connection between the Fock space introduced by Ashtekar and Pierri for Einstein-Rosen waves and its perturbative counterpart based on the concept of a particle that arises in linearized gravity with a de Donder gauge. We show that the gauge adopted by Ashtekar and Pierri is indeed a generalization of the de Donder gauge to full (i.e., non-linearized) cylindrical gravity. This fact allows us to relate the two descriptions of the Einstein-Rosen waves analyzed here (the perturbative one and that made by Ashtekar and Pierri) by means of a simple field redefinition. Employing this redefinition, we find the highly non-linear relation that exists between the annihilation and creation-like variables of the two approaches. We next represent the particle-like variables of the perturbative approach as regularized operators, introducing a cutoff. These can be expanded in powers of the annihilation and creation operators of the Ashtekar-Pierri quantization, each additional power being multiplied by an extra square root of $(ħ$ times) the three-dimensional gravitational constant, $\sqrt{G}.$ In principle, the perturbative vacuum may be reached as the limit of a state annihilated by these regularized operators when the cutoff is removed. This state can be written as the vacuum of the Ashtekar-Pierri quantization corrected by a perturbative series in $\sqrt{G}$ with no contributions from particles with energies above the cutoff. We show that the first-order correction is in fact a state of infinite norm. This result is interpreted as indicating that the Fock quantizations in the two approaches are unitarily inequivalent and, in any case, proves that the perturbative vacuum is not analytic in the interaction constant. Therefore a standard perturbative quantum analysis fails.

All three-dimensional matter-free space-times with negative cosmological constant, compatible with cyclic symmetry, are identified. The only cyclic solutions are the $2+1$ (BTZ) black hole with $\mathrm{SO}\left(2\right)\mathrm{}\times R$ isometry, and the self-dual Coussaert-Henneaux space-times, with isometry groups $\mathrm{SO}\left(2\right)\mathrm{}\times \mathrm{SO}(2,1)\mathrm{}$ or $\mathrm{SO}\left(2\right)\mathrm{}\times \mathrm{SO}\left(2\right).$

We study the propagation of classical electromagnetic waves on the simplest four-dimensional spherically symmetric metric with a dilaton background field. Solutions to the relevant equations are obtained perturbatively in a parameter which measures the strength of the dilaton field (hence parametrizes the departure from Schwarzschild geometry). The loss of energy from outgoing modes is estimated as a back-scattering process against the dilaton background, which would affect the luminosity of stars with a dilaton field. The radiation emitted by a freely falling pointlike source on such a background is also studied by analytical and numerical methods.

Using the Ashtekar-Sen variables of loop quantum gravity, a new class of exact solutions to the equations of quantum cosmology is found for gravity coupled to a scalar field that corresponds to inflating universes. The scalar field, which has an arbitrary potential, is treated as a time variable, reducing the Hamiltonian constraint to a time-dependent Schrödinger equation. When reduced to the homogeneous and isotropic case, this is solved exactly by a set of solutions that extend the Kodama state, taking into account the time dependence of the vacuum energy. Each quantum state corresponds to a classical solution of the Hamiltonian-Jacobi equation. The study of the latter shows evidence for an attractor, suggesting a universality in the phenomena of inflation. Finally, wave packets can be constructed by superposing solutions with different ratios of kinetic to potential scalar field energy, resolving, at least in this case, the issue of normalizability of the Kodama state.

The annihilation of new dark matter candidates with masses $m_X$ in the MeV range may account for the galactic positrons that are required to explain the 511 keV $\gamma$-ray flux from the galactic bulge. We study the impact of MeV-mass thermal relic particles on the primordial synthesis of ${}^2\mathrm{H},$ ${}^4\mathrm{He},$ and ${}^7\mathrm{Li}.$ If the new particles are in thermal equilibrium with neutrinos during the nucleosynthesis epoch they increase the helium mass fraction for $m_X\lesssim 10\mathrm{MeV}$ and are thus disfavored. If they couple primarily to the electromagnetic plasma they can have the opposite effect of lowering both helium and deuterium. For $m_X=4\mathrm{}–10\mathrm{MeV}$ they can even improve the overall agreement between the predicted and observed ${}^2\mathrm{H}\hspace{0.5em}\mathrm{and}{\hspace{0.5em}}^4\mathrm{He}$ abundances.

In this paper we ask whether the phenomenon of timing noise long known in electromagnetic pulsar astronomy is likely to be important in gravitational wave (GW) observations of spinning-down neutron stars. We find that timing noise is strong enough to be of importance only in the young pulsars, which must have larger triaxialities than theory predicts for their GW emission to be detectable. However, assuming that their GW emission is detectable, we list the pulsars for which timing noise is important, either because it is strong enough that its neglect by the observer would render the source undetectable or else because it is a measurable feature of the GW signal. We also find that timing noise places a limit on the observation duration of a coherent blind GW search, and suggest that hierarchical search techniques might be able to cope with this problem. Demonstration of the presence or absence of timing noise in the GW channel would give a new probe of neutron star physics.

It is still uncertain whether the cosmic censorship conjecture is true or not. To get a new insight into this issue, we propose the concept of the border of spacetime as a generalization of the spacetime singularity and discuss its visibility. The visible border, corresponding to the naked singularity, is not only relevant to mathematical completeness of general relativity but also a window into new physics in strongly curved spacetimes, which is in principle observable.

In the framework of the Schwinger-Dyson equation and the Bethe-Salpeter equation in the improved ladder approximation, we calculate the ${\pi }^{+}-{\pi }^0$ mass difference on the same footing as the pion decay constant and the QCD S parameter (or $L_{10})$ through the difference between the vector current correlator ${\Pi }_{\mathrm{VV}}$ and the axial-vector current correlator ${\Pi }_{\mathrm{AA}}.$ We find that all the results can be fit to the experimental values for a rather large ${\Lambda }_{\mathrm{QCD}}\sim 700\mathrm{MeV}$ which reflects the “scale ambiguity.” By fitting to the calculated data using the pole saturated form of ${\Pi }_{\mathrm{VV}}-{\Pi }_{\mathrm{AA}},$ we also derive masses and decay constants of the $\rho$ meson and $a_1$ meson, which we found are consistent with the experiments rather insensitively to the scale ambiguity.

Cosmic acceleration may be the result of unknown physical processes involving either new fields in high energy physics or modifications of gravitation theory. In the latter case, such modifications are usually related to the existence of extra dimensions (which is also required by unification theories), giving rise to the so-called brane cosmology. In this paper we investigate the phenomenon of the acceleration of the Universe in a particular class of brane scenarios in which a large scale modification of gravity arises due to a gravitational leakage into extra dimensions. By using the most recent supernova observations we study the transition (deceleration/acceleration) epoch as well as the constraints imposed on the parameters characterizing the model. We show that these models provide a good description for the current supernova data, which may be indicating that the existence of extra dimensions play an important role not only in fundamental physics but also in cosmology.