We discuss a supersymmetric inverse seesaw model in which lepton flavor violating decays can be enhanced either by flavor violating slepton contributions or by the nonunitarity of the charged current mixing matrix. As an example we calculate $Br(\mu \to e\gamma )$ taking into account both heavy lepton exchange as well as supersymmetric diagrams in a minimal supergravity framework. We find that for the same neutrino parameters the rate can be enhanced with respect to seesaw model expectations, with or without supersymmetry.

Supersymmetric flavor models for the radiative generation of fermion masses offer an alternative way to solve the SUSY-$CP$ problem. We assume that the supersymmetric theory is flavor and $CP$ conserving. $CP$ violating phases are associated to the vacuum expectation values of flavor violating SUSY-breaking fields. As a consequence, phases appear at tree level only in the soft supersymmetry-breaking matrices. Using a U(2) flavor model as an example we show that it is possible to generate radiatively the first and second generation of quark masses and mixings as well as the Cabibbo-Kobayashi-Maskawa (CKM) $CP$ phase. The one-loop supersymmetric contributions to electric dipole moments are automatically zero since all the relevant parameters in the Lagrangian are flavor conserving and as a consequence real. The size of the flavor and $CP$ mixing in the SUSY-breaking sector is mostly determined by the fermion mass ratios and CKM elements. We calculate the contributions to $ϵ$, ${ϵ}^{\prime }$ and to the $CP$ asymmetries in the $B$ decays to $\psi K_s$, $\varphi K_s$, ${\eta }^{\prime }{K}_s$ and $X_s\gamma$. We analyze a case study with maximal predictivity in the fermion sector. For this worst case scenario the measurements of $\Delta m_K$, $\Delta m_B$ and $ϵ$ constrain the model requiring extremely heavy squark spectra.

We propose a supersymmetric SU(5) orbifold GUT in 5 dimensions in which supersymmetry breaking at the boundaries gives rise to split supersymmetry spectrum. The extra dimension is compactified on a $S^1/Z_2\times Z_2^{\prime }$ orbifold having two fixed points. The standard model fermions are localized in the standard model brane, where supersymmetry is broken by the nonvanishing of the $F$-term of a superfield $X$ at some intermediate scale. All scalar superpartners acquire mass at this stage. The standard model gauginos and Higgsinos remain light, since their masses are protected by $R$-symmetry and induced only by loop contributions and contact interaction in our brane. Usual features of orbifold GUTs are preserved in this scenario and proton decay and neutrino mass problems are solved.

We determine the location ${\lambda }_c$ of the mobility edge in the spectrum of the Hermitian Wilson operator in pure-gauge ensembles with plaquette, Iwasaki, and DBW2 gauge actions. The results allow mapping a portion of the (quenched) Aoki phase diagram. We use Green function techniques to study the localized and extended modes. Where ${\lambda }_c>0$ we characterize the localized modes in terms of an average support length and an average localization length, the latter determined from the asymptotic decay rate of the mode density. We argue that, since the overlap operator is commonly constructed from the Wilson operator, its range is set by the value of ${\lambda }_c^{-1}$ for the Wilson operator. It follows from our numerical results that overlap simulations carried out with a cutoff of 1 GeV, even with improved gauge actions, could be afflicted by unphysical degrees of freedom as light as 250 MeV.

We study the phase diagram of dense, locally neutral three-flavor quark matter within the framework of the Nambu–Jona-Lasinio model. In the analysis, dynamically generated quark masses are taken into account self-consistently. The phase diagram in the plane of temperature and quark chemical potential is presented. The results for two qualitatively different regimes, intermediate and strong diquark coupling strength, are presented. It is shown that the role of gapless phases diminishes with increasing diquark coupling strength.

In a diquark-diquark-antiquark picture of the pentaquark we study the decay $\Theta \to K^{+}n$ within the framework of QCD sum rules. After evaluation of the relevant three-point function, we extract the coupling $g_{\Theta nK}$ which is directly related to the pentaquark width. Restricting the decay diagrams to those with color exchange between the mesonlike and baryonlike clusters reduces the coupling constant by a factor of 4. Whereas a small decay width might be possible for a positive parity pentaquark, it seems difficult to explain the measured width for a pentaquark with negative parity.

Neutrino collective excitations are studied in the standard model at high temperatures below the symmetry breaking scale in the regime $T\gg M_{W,Z}(T)\gg gT$. Two parameters determine the properties of the collective excitations: a mass scale $m_{\nu }=gT/4$ which determines the chirally symmetric gaps in the spectrum and $\Delta =M_W^2(T)/2m_{\nu }T$. The spectrum consists of left-handed negative helicity quasiparticles, left-handed positive helicity quasiholes, and their respective antiparticles. For $\Delta <{\Delta }_c=1.275\cdots$ there are two gapped quasiparticle branches and one gapless and two gapped quasihole branches, all but the higher gapped quasiparticle branches terminate at end points. For ${\Delta }_c<\Delta <\pi /2$ the quasiparticle spectrum features a pitchfork bifurcation and for $\Delta >\pi /2$ the collective modes are gapless quasiparticles with dispersion relation below the light cone for $k\ll m_{\nu }$ approaching the free field limit for $k\gg m_{\nu }$ with a rapid crossover between the soft nonperturbative to the hard perturbative regimes for $k\sim m_{\nu }$. The decay of the vector bosons leads to a width of the collective excitations of order $g^2$ which is explicitly obtained in the limits $k=0$ and $k\gg m_{\nu }\Delta$. At high temperature this damping rate is shown to be competitive with or larger than the collisional damping rate of order $G_F^2$ for a wide range of neutrino energy.

We show that the strong self-interaction of the scalar polarization of a massive graviton can be understood in terms of the propagation of an extra ghostlike degree of freedom, thus relating strong coupling to the sixth degree of freedom discussed by Boulware and Deser in their Hamiltonian analysis of massive gravity. This enables one to understand the Vainshtein recovery of solutions of massless gravity as being due to the effect of the exchange of this ghost, which gets frozen at distances larger than the Vainshtein radius. Inside this region, we can trust the two-field Lagrangian perturbatively, while at larger distances one can use the higher derivative formulation. We also compare massive gravity with other models, namely, deconstructed theories of gravity, as well as the Dvali-Gabadadze-Porrati model. In the latter case, we argue that the Vainshtein recovery process is of a different nature, not involving a ghost degree of freedom.

The four-parameter tetrahedral neutrino mass matrix introduced earlier by the author is studied in two specific limits, both having only two parameters and resulting in ${\theta }_{13}=0$, ${\theta }_{23}=\pi /4$, and ${tan}^2{\theta }_{12}=1/2$. One limit corresponds to a recent proposal which predicts a normal ordering of neutrino masses; the other is new and allows both inverted and normal ordering.

We explore the possibility of the simultaneous determination of neutrino mass hierarchy and the $CP$ violating phase by using two identical detectors placed at different baseline distances. We focus on a possible experimental setup using a neutrino beam from the J-PARC facility in Japan with a beam power of 4 MW and megaton (Mton)-class water Cherenkov detectors, one placed in Kamioka and the other somewhere in Korea. We demonstrate, under reasonable assumptions of systematic uncertainties, that the two-detector complex with each fiducial volume of 0.27 Mton has a potential of resolving the neutrino mass hierarchy up to ${sin}^{2}2{\theta }_{13}>0.03$ (0.055) at $2\sigma$ ($3\sigma$) C.L. for any values of $\delta$ and at the same time has the sensitivity to $CP$ violation by $4+4$ years running of ${\nu }_e$ and ${\overline{\nu }}_e$ appearance measurement. The significantly enhanced sensitivity is due to clean detection of the modulation of the neutrino energy spectrum, which is enabled by the cancellation of systematic uncertainties between two identical detectors which receive the neutrino beam with the same energy spectrum in the absence of oscillations.

We report evidence for the $h_c$ state of charmonium in its ${\eta }_c\gamma$ decay mode and lack of evidence in the $J/\psi {\pi }^0$ mode. We studied these channels in $\overline{p}p$ annihilations near the center of gravity of the ${}^{3}P_J$ states, where the $h_c$ was reported in the $J/\psi {\pi }^0$ mode by E760, our previous experiment, at $3526.2\pm 0.15\pm 0.2\mathrm{MeV}$, with ${\Gamma }_R\le 1\mathrm{MeV}$. We observe an event excess in the ${\eta }_c\gamma$ mode near 3526 MeV. Testing the null hypothesis of a linearly varying background cross section against the alternate hypothesis that includes a resonance near 3526 MeV, we reject the null hypothesis with $\mathcal{P}\sim 0.001$. The resonance mass is $3525.8\pm 0.2\pm 0.2\mathrm{MeV}$ and the resonance width $\le 1\mathrm{MeV}$. We estimate $10.0\pm 3.5<{\Gamma }_{\overline{p}p}{\mathcal{B}}_{{\eta }_c\gamma }<12.0\pm 4.5\mathrm{eV}$, corresponding to fixed values $0.5<{\Gamma }_R<1.0\mathrm{MeV}$. We find no event excess within the search region in the $J/\psi {\pi }^0$ mode.

Poincaré gauge theories that, in the absence of spinning matter, reduce to the one-parameter teleparallel theory are investigated with respect to their mathematical consistency and experimental viability. It is argued that the theories can be consistently coupled to the known standard model particles. Moreover, we establish the result that in the classical limit, such theories share a large class of solutions with general relativity, containing, among others, the four classical black hole solutions (Schwarzschild, Reissner-Nordstrøm, Kerr and Kerr-Newman), as well as the complete class of Friedmannn-Robertson-Walker cosmological solutions, thereby extending older viability results that were restricted to the correct Newtonian limit and to the existence of the Schwarzschild solution.

We propose a model for gamma ray bursts in which a star subject to a high level of fermion degeneracy undergoes a phase transition to a supersymmetric state. The burst is initiated by the transition of fermion pairs to sfermion pairs which, uninhibited by the Pauli exclusion principle, can drop to the ground state of minimum momentum through photon emission. The jet structure is attributed to the Bose statistics of sfermions whereby subsequent sfermion pairs are preferentially emitted into the same state (sfermion amplification by stimulated emission). Bremsstrahlung gamma rays tend to preserve the directional information of the sfermion momenta and are themselves enhanced by stimulated emission.

The next to leading order quarkonium-hadron cross section is calculated in perturbative QCD. The corresponding leading order result was performed by Peskin more than 20 years ago using the operator product expansion. In this work, the calculation is performed using the Bethe-Salpeter amplitude and the factorization formula. The soft divergence appearing in the intermediate stages of the calculations are shown to vanish after adding all possible crossed terms, while the collinear divergences are eliminated by mass factorization. Applying the result to the Upsilon system, one finds that there are large higher order corrections near the threshold. The relevance of the present result to the charmonium case is also discussed.

We construct a spherically symmetric noncommutative space in three dimensions by foliating the space with concentric fuzzy spheres. We show how to construct a gauge theory in this space, and, in particular, we derive the noncommutative version of a Yang-Mills-Higgs theory. We find numerical monopole solutions of the equations of motion.

We study the vacuum solutions of a gravity model where Lorentz symmetry is spontaneously broken once a vector field acquires a vacuum expectation value. Results are presented for the purely radial Lorentz symmetry breaking (LSB), radial/temporal LSB and axial/temporal LSB. The purely radial LSB result corresponds to new black hole solutions. When possible, parametrized post-Newtonian parameters are computed and observational boundaries used to constrain the Lorentz symmetry breaking scale.

We present a phenomenologically motivated model which is able to give rise both to an inflationary epoch and to the present day cosmic acceleration. We introduce an approach where the energy density depends on the scale factor $a$ in such a way that a smooth transition from the inflation to the matter dominated era and then to the current accelerated expansion is achieved. We use the dimensionless coordinate distance $y(z)$ to the gold type Ia supernovae data set and to a sample comprising 20 radio galaxies, the shift parameter $\mathcal{R}$, and the acoustic peak parameter $\mathcal{A}$ to test whether the model is in agreement with observations and to constrain its main parameters. As an independent cross-check, we also compare model predictions with the look-back time to galaxy clusters and the age of the universe. Although phenomenologically inspired, the model may be theoretically motivated either resorting to a scenario with scalar and phantom fields (eventually interacting) or as an effective description arising from higher order gravity theories.

We study $B$ physics phenomenology in the scenario of split supersymmetry without $R$ parity. By assuming the constraints of bilinear (trilinear) $R$-parity violating couplings, which are introduced to solve the problem of the atmospheric (solar) neutrino mass, we show that the decay branching ratios of $B_s\to {\ell }^{+}{\ell }^{-}$ and the mixing of $B_s-{\overline{B}}_s$ can be large. Explicitly, we find that $B(B_s\to {\mu }^{+}{\mu }^{-})=O({10}^{-7})$ and $\Delta m_{B_s}=O({10}^{-9})\mathrm{GeV}$, which should be observed at future hadron colliders.

Motivated by the possibility that nonets of scalar mesons might be described as mixtures of “two quark” and “four quark” components, we further study a toy model in which corresponding chiral nonets (containing also the pseudoscalar partners) interact with each other. Although the “two quark” and “four quark” chiral fields transform identically under $\mathrm{SU}(3{)}_L\times \mathrm{SU}(3{)}_R$ transformations, they transform differently under the $\mathrm{U}(1{)}_A$ transformation which essentially counts total ($\mathrm{\text{quark}}+\mathrm{\text{antiquark}}$) content of the mesons. To implement this, we formulate an effective Lagrangian which mocks up the $\mathrm{U}(1{)}_A$ behavior of the underlying QCD. We derive generating equations which yield Ward identity type relations based only on the assumed symmetry structure. This is applied to the mass spectrum of the low lying pseudoscalars and scalars, as well as their “excitations.” Assuming isotopic spin invariance, it is possible to disentangle the amount of “two quark” vs “four quark” content in the pseudoscalar $\pi ,K,\eta$-type states and in the scalar $\kappa$-type states. It is found that a small “four quark” content in the lightest pseudoscalars is consistent with a large “four quark” content in the lightest of the scalar $\kappa$ mesons. The present toy model also allows one to easily estimate the strength of a “four quark” vacuum condensate. There seems to be a rich and interesting structure.