We construct a supersymmetric model based on $T^{\prime }\otimes Z_3\otimes Z_9$ flavor symmetry. At the leading order, the charged lepton mass matrix is not diagonal, $T^{\prime }$ is broken completely, and the hierarchy in the charged lepton masses is generated naturally. Nearly tribimaximal mixing is predicted, and subleading effects induce corrections of order ${\lambda }^2$, where $\lambda$ is the Cabibbo angle. Both the up quark and down quark mass matrices’ textures of the well-known $\mathrm{U}(2)$ flavor theory are produced at the leading order; realistic hierarchies in quark masses and Cabibbo-Kobayashi-Maskawa matrix elements are obtained. The vacuum alignment and subleading corrections are discussed in detail.

Several supersymmetric models with extended gauge structures, motivated by either grand unification or by neutrino mass generation, predict light doubly-charged Higgsinos. In this work we study productions and decays of doubly-charged Higgsinos present in left-right supersymmetric models, and show that they invariably lead to novel collider signals not found in the minimal supersymmetric model or in any of its extensions motivated by the $\mu$ problem or even in extra dimensional theories. We investigate their distinctive signatures at the Large Hadron Collider in both pair- and single-production modes, and show that they are powerful tools in determining the underlying model via the measurements at the Large Hadron Collider experiments.

We present a method to measure dominant standard model backgrounds using data containing high rapidity objects in $pp$ collisions at the Large Hadron Collider (LHC). The method is developed for analyses of early LHC data when robustness against imperfections of background modeling and detector simulation can be a key to the discovery of new physics at LHC.

We study $ep$ deep inelastic scattering and the inclusive production of prompt photon within the framework of the quasi-multi-Regge-kinematic approach, applying the quark Reggeization hypothesis. We describe structure functions $F_2$ and $F_L$ supposing that a virtual photon scatters on a Reggeized quark from a proton, via the effective gamma-Reggeon-quark vertex. It is shown that the main mechanism of the inclusive prompt photon production in $p\overline{p}$ collisions is the fusion of a Reggeized quark and a Reggeized antiquark into a photon, via the effective Regeon-Reggeon-gamma vertex. We describe the inclusive photon transverse momentum spectra measured by the CDF and D0 Collaborations within errors and without free parameters, using the Kimber-Martin-Ryskin unintegrated quark and gluon distribution functions in a proton.

The rich phenomenology of collective neutrino oscillations has been studied only in one-dimensional or spherically symmetric systems. Motivated by the nonspherical example of coalescing neutron stars, presumably the central engines of short gamma-ray bursts, we use the Liouville equation to formulate the problem for general source geometries. Assuming the neutrino ensemble displays self-maintained coherence, the problem once more becomes effectively one-dimensional along the streamlines of the overall neutrino flux. This approach for the first time provides a formal definition of the “single-angle approximation” frequently used for supernova neutrinos and allows for a natural generalization to nonspherical geometries. We study the explicit example of a disk-shaped source as a proxy for coalescing neutron stars.

It has been suggested that the interactions of energetic particles with the foamy structure of space-time thought to be generated by quantum-gravitational (QG) effects might violate Lorentz invariance, so that they do not propagate at a universal speed of light. We consider the limits that may be set on a linear or quadratic violation of Lorentz invariance in the propagation of energetic neutrinos, $v/c=[1\pm (E/M_{\nu \mathrm{QG}1})]$ or $[1\pm (E/M_{\nu \mathrm{QG}2}{)}^2]$, using data from supernova explosions and the OPERA long-baseline neutrino experiment. Using the SN1987a neutrino data from the Kamioka II, IMB, and Baksan experiments, we set the limits $M_{\nu \mathrm{QG}1}>2.7(2.5)\times {10}^{10}\mathrm{GeV}$ for subluminal (superluminal) propagation and $M_{\nu \mathrm{QG}2}>4.6(4.1)\times {10}^4\mathrm{GeV}$ at the 95% confidence level. A future galactic supernova at a distance of 10 kpc would have sensitivity to $M_{\nu \mathrm{QG}1}>2(4)\times {10}^{11}\mathrm{GeV}$ for subluminal (superluminal) propagation and $M_{\nu \mathrm{QG}2}>2(4)\times {10}^5\mathrm{GeV}$. With the current CERN neutrinos to Gran Sasso extraction spill length of $10.5\mu \mathrm{s}$ and with standard clock synchronization techniques, the sensitivity of the OPERA experiment would reach $M_{\nu \mathrm{QG}1}\sim 7\times {10}^5\mathrm{GeV}$ ($M_{\nu \mathrm{QG}2}\sim 8\times {10}^3\mathrm{GeV}$) after 5 years of nominal running. If the time structure of the super proton synchrotron radio frequency bunches within the extracted CERN neutrinos to Gran Sasso spills could be exploited, these figures would be significantly improved to $M_{\nu \mathrm{QG}1}\sim 5\times {10}^7\mathrm{GeV}$ ($M_{\nu \mathrm{QG}2}\sim 4\times {10}^4\mathrm{GeV}$). These results can be improved further if a similar time resolution can be achieved with neutrino events occurring in the rock upstream of the OPERA detector: we find potential sensitivities to $M_{\nu \mathrm{QG}1}\sim 4\times {10}^8\mathrm{GeV}$ and $M_{\nu \mathrm{QG}2}\sim 7\times {10}^5\mathrm{GeV}$.

We construct actions of higher spin fields interacting with gravity on ${\mathrm{AdS}}_5$ backgrounds such that the Compton scattering amplitudes of the interaction are tree-level unitary. We then consider higher spin fields in the Randall-Sundrum scenario. There, in the fermionic case, we construct a tree-level unitary action of higher spin fields interacting with branes and linearized gravity. In the bosonic case we show that this is not in general possible. A tree-level unitary action of bosonic higher spins interacting with linearized gravity and branes is only possible in the following cases: the brane is a pure tension brane and/or Dirichlet boundary conditions are imposed thereby making bosonic higher spin fields invisible to a brane observer. We finally show that higher spins in Randall-Sundrum II braneworlds can only be produced by (decay into) gravitons at trans-Planckian scales. We end by commenting on the possible relevance of higher spin unparticles as dark matter candidates.

Lepton-flavor symmetry in the standard model is broken by small masses for charged leptons and neutrinos. Introducing neutrino masses via dimension-5 operators associated to lepton-number violation at a very high scale, the corresponding coupling matrix may still have entries of order 1, resembling the situation in the quark sector with large top Yukawa coupling. As we have shown recently, in such a situation one may introduce the coupling matrices between lepton and Higgs fields as nonlinear representations of lepton-flavor symmetry within an effective-theory framework. This allows us to separate the effects related to the large mass difference observed in atmospheric neutrino oscillations from those related to the solar mass difference. We discuss the cases of normal or inverted hierarchical and almost degenerate neutrino spectrum, give some examples to illustrate minimal lepton-flavor violation in radiative and leptonic decays, and also provide a systematic definition of next-to-minimal lepton-flavor violation within the nonlinear framework.

The vacuum persistence probability, $P_{\mathrm{vac}}(t)$, for a system of charged fermions in a fixed, external, and spatially homogeneous electric field, was derived long ago by Schwinger; $w\equiv -\log [P_{\mathrm{vac}}(t)]/Vt$ has often been identified as the rate at which fermion-antifermion pairs are produced per unit volume due to the electric field. In this paper, we separately compute exact expressions for both $w$ and for the rate of fermion-antifermion pair production per unit volume, $\Gamma$, and show that they differ. While $w$ is given by the standard Schwinger mechanism result of $w=\frac{(qE{)}^2}{4{\pi }^3}\sum _{n=1}^{\infty }\frac{1}{n^2}\exp (-\frac{n\pi m^2}{qE})$, the pair production rate, $\Gamma$, is just the first term of that series. Our calculation is done for a system with periodic boundary conditions in the $A_0=0$ gauge but the result should hold for any consistent set of boundary conditions. We discuss, the physical reason why the rates $w$ and $\Gamma$ differ.

We study the possible signatures of nonuniversal scalar masses in supersymmetry at the Large Hadron Collider (LHC). This is done, following our recent study on gaugino nonuniversality, via a multichannel analysis, based largely on the ratios of event rates for different final states, aimed at minimizing irregularity in the pattern due to extraneous effects and errors. We have studied (a) squark-slepton nonuniversality, (b) nonuniversality in sfermion masses of the third family, (c) the effects of SO(10) $D$-terms in supersymmetric grand unified theories. After presenting an elaborate numerical analysis of like- and opposite-sign dileptons, inclusive and hadronically quiet trileptons, as well as inclusive jet final states, we point out specific features of the spectrum in each case, which can be differentiated in the above channels from the spectrum for a minimal supergravity scenario with a universal scalar mass at high scale. The event selection criteria and the situations where the signals are sizable enough for a comparative study, are also delineated. It is found that, with some exceptions, the trilepton channels are likely to be especially useful for this purpose.

We provide a model-independent determination of the quantity $B_0(m_d-m_u)$. Our approach rests only on chiral symmetry and data from the decay of the eta into three neutral pions. Since the low-energy prediction at next-to-leading order fails to reproduce the experimental results, we keep the strong interaction correction as an unknown parameter. As a first step, we relate this parameter to the quark mass difference using data from the Dalitz plot. A similar relation is obtained using data from the decay width. Combining both relations we obtain $B_0(m_d-m_u)=(4495\pm 440){\mathrm{MeV}}^2$. The preceding value, combined with lattice determinations, leads to the values $m_u(2\mathrm{GeV})=(2.9\pm 0.8)\mathrm{MeV}$ and $m_d(2\mathrm{GeV})=(4.7\pm 0.8)\mathrm{MeV}$.

We present a construction of the pion electromagnetic form factor where the transition from large-$N_c$ Regge vector-meson dominance models with infinitely many resonances to perturbative QCD is built in explicitly. The construction is based on an appropriate assignment of residues to the Regge poles, which fulfills the constraints of the parton-hadron duality and perturbative QCD. The model contains a slowly falling off nonperturbative contribution, which dominates over the perturbative QCD radiative corrections for the experimentally accessible momenta. The leading order and next-to-leading order calculations show a converging pattern that describes the available data within uncertainties, while the onset of asymptotic QCD takes place at extremely high momenta $Q\sim {10}^3–{10}^4\mathrm{GeV}$. The method can be straightforwardly extended to study other form factors where the perturbative QCD result is available.

Using the previous Belle measurement of the inclusive photon energy in $B\to X_s\gamma$ decays, we determine the first and second moments of this spectrum for minimum photon energies in the $B$ meson rest frame ranging from 1.8 to 2.3 GeV. Combining these measurements with recent Belle data on the lepton energy and hadronic mass moments in $B\to X_c\ell \nu$ decays, we perform fits to theoretical expressions derived in the 1S and kinetic mass schemes and extract the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $V_{cb}$, the $b$-quark mass, and other nonperturbative parameters. In the 1S scheme analysis we find $|V_{cb}|=(41.56\pm 0.68(\mathrm{\text{fit}})\pm 0.08({\tau }_B))\times {10}^{-3}$ and $m_b^{1\mathrm{S}}=(4.723\pm 0.055)\mathrm{GeV}$. In the kinetic scheme, we obtain $|V_{cb}|=(41.58\pm 0.69(\mathrm{\text{fit}})\pm 0.08({\tau }_B)\pm 0.58(\mathrm{th}))\times {10}^{-3}$ and $m_b^{\mathrm{kin}}=(4.543\pm 0.075)\mathrm{GeV}$.

We derive an analytical description of neutrino oscillations in matter based on the Magnus exponential representation of the time evolution operator. Our approach is valid in a wide range of the neutrino energies and properly accounts for the modifications that the respective probability transitions suffer when neutrinos originated in different sources traverse the Earth. The present approximation considerably improves over other perturbative treatments existing in the current literature. Furthermore, the analytical expressions derived inside the Magnus framework are remarkably simple, which facilitates their practical use. When applied to the calculation of the day-night asymmetry in the solar neutrino flux our result reproduces the numerical calculation with an accuracy better than 1% for the first-order approximation. When the approximation is extended to the second order, the accuracy of the method is further improved by almost 1 order of magnitude, and it is still better than 5% even for neutrino energies as large as 100 MeV. In the GeV regime characteristic of atmospheric and accelerator neutrinos this accuracy is complemented by a good reproduction of the position of the maxima in the flavor transition probabilities.

We investigate the effects of the purely toroidal magnetic field on the equilibrium structures of the relativistic stars. The basic equations for obtaining equilibrium solutions of relativistic rotating stars containing purely toroidal magnetic fields are derived for the first time. To solve these basic equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for calculating relativistic rotating stars containing no magnetic field to incorporate the effects of the purely toroidal magnetic fields. By using the numerical scheme, we then calculate a large number of the equilibrium configurations for a particular distribution of the magnetic field in order to explore the equilibrium properties. We also construct the equilibrium sequences of the constant baryon mass and/or the constant magnetic flux, which model the evolution of an isolated neutron star as it loses angular momentum via the gravitational waves. Important properties of the equilibrium configurations of the magnetized stars obtained in this study are summarized as follows: (1) For the nonrotating stars, the matter distribution of the stars is prolately distorted due to the toroidal magnetic fields. (2) For the rapidly rotating stars, the shape of the stellar surface becomes oblate because of the centrifugal force. But, the matter distribution deep inside the star is sufficiently prolate for the mean matter distribution of the star to be prolate. (3) The stronger toroidal magnetic fields lead to the mass shedding of the stars at the lower angular velocity. (4) For some equilibrium sequences of the constant baryon mass and magnetic flux, the stars can spin up as they lose angular momentum.

We present an analytic derivation of Hawking radiation for an arbitrary (spatial) dispersion relation $\omega (k)$ as a model for ultrahigh-energy deviations from general covariance. It turns out that the Hawking temperature is proportional to the product of the group $d\omega /dk$ and phase $\omega /k$ velocities evaluated at the frequency $\omega$ of the outgoing radiation far away, which suggests that Hawking radiation is basically a low-energy phenomenon. Nevertheless, a group velocity growing too fast at ultrashort distances would generate Hawking radiation at ultrahigh energies (“ultraviolet catastrophe”) and hence should not be a realistic model for the microscopic structure of quantum gravity.

Events with three or more isolated leptons in the final state are known to be signatures of new physics phenomena at high energy collider physics facilities. Standard model sources of isolated trilepton final states include gauge boson pair production such as $WZ$ and $W{\gamma }^{*}$, and $t\overline{t}$ production. We demonstrate that leptons from heavy flavor decays, such as $b\to lX$ and $c\to lX$, provide sources of trileptons that can be orders of magnitude larger after cuts than other standard model backgrounds to new physics processes. We explain the physical reason heavy flavor backgrounds survive isolation cuts. We propose new cuts to control the backgrounds in the specific case of chargino plus neutralino pair production in supersymmetric models. After these cuts are imposed, we show that it should be possible to find at least a $4\sigma$ excess for supersymmetry parameter space point LM9 with $30{\mathrm{fb}}^{-1}$ of integrated luminosity.

In the framework of a toy model which possesses the main features of QCD in the high-energy limit, we conduct a numerical study of scattering amplitudes constructed from parton splittings and projectile-target multiple interactions, in a way that unitarizes the amplitudes without however explicit saturation in the wave function of the incoming states. This calculation is performed in two different ways. One of these formulations, the closest to field theory, involves the numerical resummation of a factorially divergent series, for which we develop appropriate numerical tools. We accurately compare the properties of the resulting amplitudes with what would be expected if saturation were explicitly included in the evolution of the states. We observe that the amplitudes have similar properties in a small but finite range of rapidity in the beginning of the evolution, as expected. Some of the features of reaction-diffusion processes are already present in that range, even when wave function saturation is left out of the model.

The processes of exclusive photo- and electroproduction of vector mesons ${\rho }^0(770)$, $\varphi (1020)$, and $J/\psi (3096)$ at collision energies $30\mathrm{GeV}<W<300\mathrm{GeV}$ and transferred momenta squared $0<-t<2{\mathrm{GeV}}^2$ are considered in the framework of a phenomenological Regge-eikonal scheme with nonlinear Regge trajectories in which their QCD asymptotic behavior is taken into account explicitly. By comparison of available experimental data from ZEUS and H1 Collaborations with the model predictions it is demonstrated that corresponding angular distributions and integrated cross sections in the above-mentioned kinematical range can be quantitatively described with use of two $C$-even vacuum Regge trajectories. These are the “soft” Pomeron dominating the high-energy reactions without a hard scale and the “hard” Pomeron giving an essential contribution to photo- and electroproduction of heavy vector mesons and deeply virtual electroproduction of light vector mesons.

Quasirealistic string models in the free fermionic formulation typically contain an anomalous $U(1)$, which gives rise to a Fayet-Iliopoulos $D$-term that breaks supersymmetry at the one-loop level in string perturbation theory. Supersymmetry is traditionally restored by imposing $F$ and $D$ flatness on the vacuum. By employing the standard analysis of flat directions, we present a quasirealistic three-generation string model in which stringent $F$- and $D$-flat solutions do not appear to exist to all orders in the superpotential. We speculate that this result is indicative of the nonexistence of supersymmetric flat $F$ and $D$ solutions in this model. We provide some arguments in support of this scenario and discuss its potential implications. Bose-Fermi degeneracy of the string spectrum implies that the one-loop partition function, and hence the one-loop cosmological constant, vanishes in the model. If our assertion is correct, this model may represent the first known example with vanishing cosmological constant and perturbatively broken supersymmetry. We discuss the distinctive properties of the internal free fermion boundary conditions that may correspond to a large set of models that share these properties. The geometrical moduli in this class of models are fixed due to asymmetric boundary conditions, whereas absence of supersymmetric flat directions would imply that the supersymmetric moduli are fixed as well and the dilaton may be fixed by hidden sector nonperturbative effects.