The partonic energy loss has been calculated taking both the hard and soft contributions for all the $2\to 2$ processes, revealing the importance of the individual channels. Cancellation of the intermediate separation scale has been exhibited. Subtleties related to the identical final state partons have properly been taken into account. The estimated collisional loss is compared with its radiative counter part. We show that there exists a critical energy ($E_c$) below which the collisional loss is more than its radiative counterpart. In addition, we present closed form formulas for both the collision probabilities and the stopping power ($dE/dx$).

Based on quantum fluctuations in momentum and of the proton into meson-baryon pairs, we develop a physical model for the nonperturbative $x$ shape of parton density functions in the proton. The model describes the proton structure function and gives a natural explanation of observed quark asymmetries, such as the difference between the anti-up and anti-down sea quark distributions and between the up and down valence distributions. An asymmetry in the momentum distribution of strange and antistrange quarks in the nucleon is found to reduce the NuTeV anomaly to a level which does not give a significant indication of physics beyond the standard model.

We investigate the relation between the $E_{\gamma }$ spectrum in $B\to X_s\gamma$ decay and the $P_{+}$ spectrum in semileptonic $B\to X_u\ell \overline{\nu }$ decay ($P_{+}$ is the hadronic energy minus the absolute value of the hadronic three-momentum), which provides in principle the theoretically simplest determination of $|V_{ub}|$ from any of the “shape function regions” of $B\to X_u\ell \overline{\nu }$ spectra. We calculate analytically the $P_{+}$ spectrum to order ${\alpha }_s^2{\beta }_0$, and study its relation to the $B\to X_s\gamma$ photon spectrum to eliminate the leading dependence on nonperturbative effects. We compare the result of fixed order perturbation theory to the next-to-leading log renormalization group improved calculation, and argue that fixed order perturbation theory is likely to be a more appropriate expansion. Implications for the perturbative uncertainties in the determination of $|V_{ub}|$ from the $P_{+}$ spectrum are discussed.

Recently bulk Randall-Sundrum theories with the gauge group $SU(2{)}_L\times SU(2{)}_R\times U(1{)}_{B-L}$ have drawn a lot of interest as an alternative to the electroweak symmetry breaking mechanism. These models are in better agreement with electroweak precision data since custodial isospin symmetry on the IR-brane is protected by the extended bulk gauge symmetry. We comprehensively study, in the $S^1/{\mathbb{Z}}_2\times {\mathbb{Z}}_2^{\prime }$ orbifold, the bulk gauge and fermion fields with the general boundary conditions as well as the bulk and localized mass terms. Master equations to determine the Kaluza-Klein (KK) mass spectra are derived without any approximation, which is an important basic step for various phenomenologies at high energy colliders. The correspondence between orbifold boundary conditions and localized mass terms is demonstrated not only in the gauge sector but also in the fermion sector. As the localized mass increases, the first KK fermion mass is shown to decrease while the first KK gauge boson mass is shown to increase. The degree of gauge coupling universality violation is computed to be small in most parameter space, and its correlation with the mass difference between the top quark and light quark KK mode is also studied.

The standard, scale-invariant, inflationary perturbation spectrum will be modified if the effects of trans-Planckian physics are incorporated into the dynamics of the matter field in a phenomenological manner, say, by the modification of the dispersion relation. The spectrum also changes if we retain the standard dynamics but modify the initial quantum state of the matter field. We show that, given any spectrum of perturbations, it is possible to choose a class of initial quantum states which can exactly reproduce this spectrum with the standard dynamics. We provide an explicit construction of the quantum state which will produce the given spectrum. We find that the various modified spectra that have been recently obtained from “trans-Planckian considerations” can be constructed from suitable squeezed states above the Bunch-Davies vacuum in the standard theory. Hence, the CMB observations can, at most, be useful in determining the initial state of the matter field in the standard theory, but it can not help us to discriminate between the various Planck scale models of matter fields. We study the problem in the Schrodinger picture and determine the criterion for negligible back reaction due to modified initial conditions.

Recently, a relativistic gravitation theory has been proposed [J. D. Bekenstein, Phys. Rev. D 70, 083509 (2004)] that gives the modified Newtonian dynamics in the weak acceleration regime. The theory is based on three dynamic gravitational fields and succeeds in explaining a large part of extragalactic and gravitational lensing phenomenology without invoking dark matter. In this work, I consider the strong gravity regime of TeVeS. I study spherically symmetric, static, and vacuum spacetimes relevant for a nonrotating black hole or the exterior of a star. Two branches of solutions are identified: in the first, the vector field is aligned with the time direction, while in the second, the vector field has a nonvanishing radial component. I show that in the first branch of solutions the $\beta$ and $\gamma$ parametrized post-Newtonian (PPN) coefficients in TeVeS are identical to these of general relativity, while in the second the $\beta$ PPN coefficient differs from unity, violating observational determinations of it (for the choice of the free function $F$ of the theory made in Bekenstein’s paper). For the first branch of solutions, I derive analytic expressions for the physical metric and discuss their implications. Applying these solutions to the case of black holes, it is shown that they violate causality (since they allow for superluminal propagation of metric, vector, and scalar waves) in the vicinity of the event horizon and/or that they are characterized by negative energy density carried by the fields.

In recently introduced split supersymmetry (SUSY) theories, in which the scale of SUSY breaking is very high, the requirement that the relic abundance of the lightest superpartner (LSP) provides the dark matter of the Universe leads to the prediction of fermionic superpartners around the weak scale. This is no longer obviously the case if the LSP is a hidden sector field, such as a gravitino or another hidden sector fermion, so it is interesting to study this scenario. We consider the case in which the next-lightest superpartner (NLSP) freezes out with its thermal relic abundance, and then it decays to the LSP. We use the constraints from big bang nucleosynthesis and cosmic microwave background, together with the requirement of attaining gauge coupling unification and that the LSP abundance provides the dark matter of the Universe, to infer the allowed superpartner spectrum. As very good news for detection of split SUSY at LHC, we find that if the gravitino is the LSP, then the only allowed NLSP has to be very purely photinolike. In this case, a photino from 700 GeV to 5 TeV is allowed, which is difficult to test at LHC. We also study the case where the LSP is given by a light fermion in the hidden sector which is naturally present in SUSY breaking in extra dimensions. We find that, in this case, a generic NLSP is allowed to be in the range 1–20 TeV, while a bino NLSP can be as light as tens of GeV.

The neutrinoless double beta decay is one of the few phenomena, belonging to the nonstandard physics, which is extensively being sought for in experiments. In the present paper the link between the half-life of the neutrinoless double beta decay and theories with large extra dimensions is explored. The use of the sensitivities of currently planned $0\nu 2\beta$ experiments: DAMA, CANDLES, COBRA, DCBA, CAMEO, GENIUS, GEM, MAJORANA, MOON, CUORE, EXO, and XMASS, gives the possibility for a nondirect “experimental” verification of various extra dimensional scenarios. We discuss also the results of the Heidelberg-Moscow Collaboration. The calculations are based on the Majorana neutrino mass generation mechanism in the Arkani-Hamed-Dimopoulos-Dvali model.

In this paper, we analyze the scattering of the neutrino beam on the polarized electron target, and predict the effects of two theoretically possible scenarios beyond the standard model. In both scenarios, our results are presented in a massless neutrino limit. First, we consider how the existence of $CP$ violation phase between the complex vector $V$ and axial $A$ couplings of the left-handed neutrinos affects the azimuthal dependence of the differential cross section. The azimuthal angle ${\varphi }_{e^{\prime }}$ of outgoing electron momentum is measured with respect to the transverse component of the initial electron polarization ${\mathit{\eta }}_{\mathit{e}}^{\perp }$. We indicate the possibility of using the polarized electron target to measure the $CP$ violation in the ${\nu }_{\mu }{e}^{-}$ scattering. The future superbeam and neutrino factory experiments will provide the unique opportunity for the leptonic $CP$ violation studies, if the large magnetized sampling calorimeters with good event reconstruction capabilities are build. Next, we take into account a scenario with the participation of the exotic complex scalar $S$ coupling of the right-handed neutrinos in addition to the standard real vector $V$ and axial $A$ couplings of the left-handed neutrinos. The main goal is to show how the presence of the $R$-handed neutrinos, in the above process changes the spectrum of recoil electrons in relation to the expected standard model prediction, using the current limits on the nonstandard couplings. The interference terms between the standard and exotic couplings in the differential cross section depend on the angle $\alpha$ between the transverse incoming neutrino polarization and the transverse electron polarization of the target. The detection of the dependence on this angle in the energy spectrum of recoil electrons would be a signature of the presence of the $R$-handed neutrinos in the neutrino-electron scattering. To make this test feasible, the polarized artificial neutrino source needs to be identified.

We study one-dimensional intersections of M5 branes with M5 and M2 branes. On the worldvolume of the M5-brane, such an intersection appears as a string soliton. We study this worldvolume theory in two different regimes: (1) Where the world-volume theory is formulated in flat space and (2) where the world-volume theory is studied in the supergravity background produced by a stack of M5 (or M2) branes. In both cases, we study the corresponding string solitons, and find the most general BPS configuration consistent with the fraction of supersymmetries preserved. We argue that M5 and M2 brane intersections leave different imprints on the world-volume theory of the intersecting probe brane, although geometrically they appear to be similar.

We derive 5D $\mathcal{N}=1$ superspace action including the radion superfield. The radion is treated as a dynamical field and identified as a solution of the equation of motion even in the presence of the radius stabilization mechanism. Our derivation is systematic and based on the superconformal formulation of 5D supergravity. We can read off the couplings of the dynamical radion superfield to the matter superfields from our result. The correct radion mass can be obtained by calculating the radion potential from our superspace action.

Inflation has the potential to seed the galactic magnetic fields observed today. However, there is an obstacle to the amplification of the quantum fluctuations of the electromagnetic field during inflation: namely, the conformal invariance of electromagnetic theory on a conformally flat underlying geometry. As the existence of a preferred minimal length breaks the conformal invariance of the background geometry, it is plausible that this effect could induce electromagnetic field amplification. We show that this scenario is equivalent to endowing the photon with a large negative mass during inflation. This effective mass is negligibly small in a radiation and matter-dominated universe. Depending on the value of the free parameter in the theory, we show that the seed required by the dynamo mechanism can be generated. We also show that this mechanism can produce the requisite galactic magnetic field without resorting to a dynamo mechanism.

We compute the bulk viscosity of a mixed quark-hadron phase. In the first scenario to be discussed, the mixed phase occurs at large densities and we assume that it is composed of a mixing of hyperonic matter and quarks in the Color Flavor Locked phase. In a second scenario, the mixed phase occurs at lower densities and it is composed of a mixing of nucleons and unpaired quark matter. We have also investigated the effect of a nonvanishing surface tension at the interface between hadronic and quark matter. In both scenarios, the bulk viscosity is large when the surface tension is absent, while the value of the viscosity reduces in the second scenario when a finite value for the surface tension is taken into account. In all cases, the r-mode instabilities of the corresponding hybrid star are suppressed.

We study the recently proposed Lorentz-violating dispersion relation for fermions and show that it leads to two distinct cubic operators in the momentum. We compute the leading order terms that modify the nonrelativistic equations of motion and use experimental results for the hyperfine transition in the ground state of the ${}^9\mathrm{B}{e}^{+}$ ion to bound the values of the Lorentz-violating parameters ${\eta }_1$ and ${\eta }_2$ for neutrons. The resulting bounds depend on the value of the Lorenz-violating background four-vector in the laboratory frame.

The effective interactions which violate lepton flavor accompanied with neutrinos (nLFV) are considered. Such new physics effects are expected to be measured in future neutrino oscillation experiments with a long baseline. They are induced by radiative corrections in the framework of the minimal supersymmetric standard model with right-handed neutrinos. We numerically evaluate the size of nLFV interactions in this framework. The slepton mixing is not only the origin of lepton flavor violation in the charged lepton sector (cLFV) but also that of the nLFV. We find that the nLFV couplings are strongly correlated with the corresponding cLFV processes, and they are constrained to be $\mathcal{O}({10}^{-5})$ times smaller than the standard four-Fermi couplings.

Sneutrino resonances at a high-energy linear $e^{+}{e}^{-}$ collider may be one of the clearest signals of supersymmetry without $R$ parity, especially when the $R$-parity-violating coupling is too small to produce observable excesses in four-fermion processes. However, there is no guarantee that the sneutrino pole will lie anywhere near the machine energy. We show that associated photon production induces the necessary energy spread, and that the resonance then leaves a clear imprint in the photon spectrum. It follows that tagging of a hard monoenergetic photon for a variety of possible final states provides a realistic method of separating sneutrino resonance signals from the standard model backgrounds.

We calculate the two-pion wave function in the ground state of the $I=2$ $S$-wave system and find the interaction range between two pions, which allows us to examine the validity of the necessary condition for the finite-volume method for the scattering length proposed by Lüscher. We work in the quenched approximation employing a renormalization group improved gauge action for gluons and an improved Wilson action for quarks at $1/a=1.207(12)\mathrm{GeV}$ on ${16}^3\times 80$, ${20}^3\times 80$, and ${24}^3\times 80$ lattices. We conclude that the necessary condition is satisfied within the statistical errors for the lattice sizes $L\ge 24$ (3.92 fm) when the quark mass is in the range that corresponds to $m_{\pi }^2=0.273–0.736{\mathrm{GeV}}^2$. We obtain the scattering length with a smaller statistical error from the wave function than from the two-pion time correlator.

The asymmetries of both light-flavor antiquark $\overline{d}(x)-\overline{u}(x)$ and strange-antistrange $s(x)-\overline{s}(x)$ distributions of the nucleon sea are considered with more details in the effective chiral quark model. We find that the asymmetric distribution of light-flavor antiquarks $\overline{d}(x)-\overline{u}(x)$ matches the experimental data well and that the asymmetry of strange and antistrange distributions can bring about 60%–100% correction to the NuTeV anomaly of ${sin}^2{\theta }_w$, which are 3 standard deviations from the world average value measured in other electroweak processes. The results on the correction to the NuTeV anomaly are insensitive to the inputs of the constituent quark distributions and the cutoff parameters. The ratios of $\overline{d}(x)/\overline{u}(x)$ and $s(x)/\overline{s}(x)$ are also discussed, and it is found that the ratio $s(x)/\overline{s}(x)$ is compatible with the available experiments with an additional symmetric sea contribution being considered effectively.

We present new sets of nonperturbative fragmentation functions for $D^0$, $D^{+}$, and $D_s^{+}$ mesons as well as for ${\Lambda }_c^{+}$ baryons, both at leading and next-to-leading order in the $\overline{\mathrm{MS}}$ factorization scheme with five massless quark flavors. They are determined by fitting data of $e^{+}{e}^{-}$ annihilation taken by the OPAL Collaboration at CERN LEP1. We take the charm-quark fragmentation function to be of the form proposed by Peterson et al. and thus obtain new values of the ${ϵ}_c$ parameter, which are specific for our choice of factorization scheme.

We present a search for $ZZ$ and $ZW$ vector boson pair production in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using the leptonic decay channels $ZZ\to ll\nu \nu$, $ZZ\to ll{l}^{\prime }{l}^{\prime }$, and $ZW\to ll{l}^{\prime }\nu$. In a data sample corresponding to an integrated luminosity of $194{\mathrm{pb}}^{-1}$ collected with the Collider Detector at Fermilab, 3 candidate events are found with an expected background of $1.0\pm 0.2$ events. We set a 95% confidence level upper limit of 15.2 pb on the cross section for $ZZ$ plus $ZW$ production, compared to the standard model prediction of $5.0\pm 0.4\mathrm{pb}$.