$Z^{\prime }$ bosons are known to naturally exist in well-motivated extensions of the standard model. The leptophobic $Z^{\prime }$ gauge boson can appear in models with $E_6$ gauge symmetry due to the mixing of the gauge-boson kinetic terms. We show that flavor-changing neutral currents can be generated in some of these models due to the mixing of the ordinary $d_R,$ $s_R,$ and $b_R$ quark fields with the exotic $h_R,$ where exotic $h_R$ means an exotic vector-singlet charge $-1/3$ quark $h.\mathrm{}$ Since the $Z^{\prime }$ boson does not couple to charged leptons, the constraints on the flavor-changing couplings $U_{\mathrm{db}}^{Z^{\prime }}$ and $U_{\mathrm{sb}}^{Z^{\prime }}$ are relatively weak. $B_q^0-\overline{B_q^0}$ mixing $\mathrm{}(q=d,s)\mathrm{}$ can be dominated by $Z^{\prime }$-mediated flavor-changing neutral currents.

We analyze supersymmetric contributions to $B_s$ mixing and their impact on mixing-induced CP asymmetries, using the mass insertion approximation. We discuss in particular the correlation of supersymmetry (SUSY) effects in the CP asymmetries of $B_s\to J/\psi \phi$ and $B_d\to \phi K_S$ and find that the mass insertions dominant in $B_s$ mixing and $B_d\to \phi K_S$ are $({\delta }_{23}^d{)}_{LL,RR}$ and $({\delta }_{23}^d{)}_{LR,RL},$ respectively. We show that models with dominant $({\delta }_{23}^d{)}_{LR,RL}$ can accommodate a negative value of $S_{\phi K_S},$ in agreement with the Belle measurement of that observable, but yield a $B_s$ mixing phase too small to be observed. On the other hand, models with dominant $({\delta }_{23}^d{)}_{LL,RR}$ predict sizable SUSY contributions to both $\Delta M_s$ and the mixing phase, but do not allow the asymmetry in $B_d\to \phi K_S$ to become negative, except for small values of the average down squark mass, which, in turn, entail a value of $\Delta M_s$ too large to be observed at the Fermilab Tevatron and CERN LHC. We conclude that the observation of $B_s$ mixing at hadron machines, together with the confirmation of a negative value of $S_{\phi K_S},$ disfavors models with a single dominant mass insertion.

In this paper, we focus on the role of power corrections in the QCD factorization (QCDF) method in charmless two-body nonleptonic B meson decays. We use the ratio of the branching fraction of $B^{+}\to {\pi }^{+}{K}^{*0}$ to that of $B^0\to {\pi }^{-}{\rho }^{+},$ for which the theoretical uncertainties are greatly reduced, to show clearly that the power corrections in charmless B decays are probably large. With other similar ratios considered, for example, for the $B^0\to K^{-}{\rho }^{+}$ decay, it is very likely that, among various sources of power corrections, annihilation topology plays an indispensable role at least for penguin dominated PV channels. We also consider some selective ratios of direct CP asymmetries. Among these, we find that, if power corrections other than the chirally enhanced power corrections and annihilation topology were negligible, QCDF would predict the direct CP asymmetry of $\overrightarrow{B}{\pi }^{+}{\pi }^{-}$ to be about 3 times larger than that of $\overrightarrow{B}{\pi }^{\pm }{K}^{\mp },$ with opposite sign. Experimentally any significant deviation from this prediction would suggest either new physics or possibly the importance of long-distance rescattering effects.

We study the exclusive semileptonic decays $B_s\to D_{s0\mathrm{}}^{*}\mathcal{l}\overline{\nu }$ and $B_s\to D_{s1\mathrm{}}^{*}\mathcal{l}\overline{\nu },$ where p-wave excited $D_{s0\mathrm{}}^{*}$ and $D_{s1\mathrm{}}^{*}$ states are identified with the newly observed $D_{\mathrm{sJ}}\mathrm{}\left(2317\right)\mathrm{}$ and $D_{\mathrm{sJ}}\mathrm{}\left(2460\right)\mathrm{}$ states. Within the framework of heavy quark effective theory the Isgur-Wise functions up to the subleading order of the heavy quark expansion are calculated by QCD sum rules. The decay rates and branching ratios are computed with the inclusion of corrections of order ${1/m}_Q.$ We point out that investigation of $B_s$ semileptonic decays to excited $D_s$ mesons may provide some information about the nature of the new $D_{\mathrm{sJ}}^{*}$ mesons.

We study the QCD corrections to neutrino deep-inelastic scattering on a nucleus, and analytically estimate their size. For an isoscalar target, we show that the dominant QCD corrections to the ratio of the neutral- to charged-current events are suppressed by ${\sin }^4{\theta }_W,$ where ${\theta }_W$ is the weak mixing angle. We then discuss the implications for the NuTeV determination of ${\sin }^2{\theta }_W.$

We consider the production of heavy $\mathrm{}(b,t)\mathrm{}$ quark pairs at proton colliders in the theoretical framework of the MSSM. Under the assumption of a “moderately” light SUSY scenario, we first compute the leading logarithmic MSSM contributions at one loop for the elementary processes of production from a quark and from a gluon pair in the 1 TeV c.m. energy region. We show that in the initial gluon pair case (dominant in the chosen situation at energies reached at the CERN LHC) the electroweak and the strong SUSY contributions concur to produce an enhanced effect whose relative value in the cross sections could reach the twenty percent size for large $\tan \beta$ values in the realistic proton-proton LHC process.

The Dirac equation is solved in the near horizon limit geometry of an extreme Kerr black hole. We decouple equations first, as usual, into an axial and angular part. The axial equation turns out to be independent of the mass and is solved exactly. The angular equation reduces, in the massless case, to a confluent Heun equation. In general for a nonzero mass, the angular equation is expressible, at best, as a set of coupled first order differential equations apt for numerical investigation. The axial potentials corresponding to the associated Schrödinger-type equations and their conserved currents are found. Finally, based on our solution, we verify in a similar way the absence of superradiance for Dirac particles in the near horizon, a result which is well known within the context of a general Kerr background.

We comprehensively study in the littlest Higgs model the phenomenology of the heavy $U\left(1\right)\mathrm{}$ gauge boson $B_H,$ which is the lightest of the newly introduced heavy gauge bosons and toplike vector quarks. Some unexpected behavior is that in the parameter space where the mass of $B_H$ is minimized the corrections to the electroweak precision observables are also suppressed. For the global symmetry breaking scale $f\lesssim 3\mathrm{TeV},$ the $B_H$ is light enough to be produced at a 500 GeV linear collider. We show that this light $B_H$ is not excluded by the direct search for the neutral heavy gauge boson at the Fermilab Tevatron in a large portion of the parameter space. Furthermore, even the light $B_H$ with a mass around 200 GeV yields negligible contributions to the muon anomalous magnetic moment, which is consistent with the current inconclusive status of the theoretical calculation of $(g-{2)}_{\mu }$ in the standard model. The effects of the littlest Higgs model on the $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ process are also studied; this is one of the most efficient processes to probe the $B_H.$

We consider the possibility that physics beyond the standard model contributes to the decays $\overrightarrow{B}{V}_1{V}_2,$ where $V_1$ and $V_2$ are vector mesons. We show that a time-dependent angular analysis of $\overrightarrow{B}{V}_1{V}_2$ decays provides many tests for this new physics (NP). Furthermore, although one cannot solve for the NP parameters, we show that this angular analysis allows one to put bounds on these parameters. This can be useful in estimating the scale of NP, and can tell us whether any NP found directly at future high-energy colliders can be responsible for effects seen in $\overrightarrow{B}{V}_1{V}_2$ decays.

We investigate the gravitational energy emission of an ultrarelativistic particle radially falling into a $D$-dimensional black hole. We numerically integrate the equations describing black hole gravitational perturbations and obtain the energy spectra, total energy, and angular distribution of the emitted gravitational radiation. The black hole quasinormal modes for scalar, vector, and tensor perturbations are computed in the WKB approximation. We discuss our results in the context of black hole production at the TeV scale.

We study the role that tachyon fields may play in cosmology as compared to the well-established use of minimally coupled scalar fields. We first elaborate on a kind of correspondence existing between tachyons and minimally coupled scalar fields; corresponding theories give rise to the same cosmological evolution for a particular choice of the initial conditions but not for any other. This leads us to study a specific one-parameter family of tachyonic models based on a perfect fluid mixed with a positive cosmological constant. For positive values of the parameter, one needs to modify Sen’s action and use the $\sigma$ process of resolution of singularities. The physics described by this model is dramatically different and much richer than that of the corresponding scalar field. For particular choices of the initial conditions, the universe, which does mimic for a long time a de Sitter–like expansion, ends up in a finite time in a special type of singularity that we call a big brake. This singularity is characterized by an infinite deceleration.

The possibility of reconstructing the dark energy equation of state from variations in the fine structure constant is investigated for a class of models where the quintessence field is nonminimally coupled to the electromagnetic field. For given classes of couplings and quintessence interaction potentials, it is typically found that variations in alpha would need to be measured to within an accuracy of at least $5\times {10}^{-7}$ to obtain a reconstructed equation of state with less than a twenty percent deviation from the true equation of state between redshifts 0 and 3. In this case, it is argued that the sign of the first derivative of the equation of state can be uncovered from the reconstruction, thus providing unique information on how the Universe developed into its present dark energy dominated phase independent of high redshift surveys. Such information would complement future observations anticipated from the Supernova Acceleration Probe.

We consider supersymmetric (SUSY) scenarios, compatible with all cosmological and phenomenological requirements, where the lightest SUSY particles (LSPs) are the neutralino and a quasidegenerate gluino. We study the neutralino relic abundance, focusing on gluino (co)annihilation effects. In case the neutralino is B-ino-like, in a wide mass window the relic abundance is naturally driven in the correct range for the LSP to be the main cold dark matter constituent. We show that the gluino is the strongest possible coannihilating partner of a B-ino-like neutralino in the general minimal supersymmetric standard model. Moreover, contrary to other coannihilation scenarios, gluino pair annihilations always dominate over coannihilation processes, even at relatively large gluino-neutralino mass splittings. Finally, we present prospects for neutralino dark matter detection in the outlined framework.

The emerging cosmological picture is of a spatially flat universe composed predominantly of three components: ordinary baryons $({\Omega }_B\approx 0.05),$ nonbaryonic dark matter $({\Omega }_{\mathrm{dark}}\approx 0.22)$ and dark energy $({\Omega }_{\Lambda }\approx 0.7).$ We recently proposed that ordinary matter was synthesized from mirror matter, motivated by the argument that the observed similarity of ${\Omega }_B$ and ${\Omega }_{\mathrm{dark}}$ suggests an underlying similarity between the fundamental properties of ordinary and dark matter particles. In this paper we generalize the previous analysis by considering a wider class of effective operators that nongravitationally couple the ordinary and mirror sectors. We find that while all considered operators imply ${\Omega }_{\mathrm{dark}}=\mathrm{few}\times {\Omega }_B,$ only a subset quantitatively reproduce the observed ratio ${\Omega }_B/{\Omega }_{\mathrm{dark}}\approx \mathrm{0.20.}$ The $\sim 1\mathrm{eV}$ mass scale induced through these operators hints at a connection with neutrino oscillation physics.

If the recently discovered charmonium state $X\left(3870\right)\mathrm{}$ is a loosely bound molecule of the charm mesons $D^0$ and $D^{*0}$ or $D^0$ and $D^{*0},$ it can be produced in $e^{+}{e}^{-}$ annihilation at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance by the coalescence of charm mesons produced in the decays of $B^{+}$ and $B^{-}$ mesons. Remarkably, in the case of 2-body decays of the B mesons, the leading contribution to the coalescence probability depends only on the hadron masses and on the width and branching fractions of the B meson. As the binding energy $E_b$ of the molecule goes to zero, the coalescence probability scales as $E_b^{1/2}\log {(E}_b).\mathrm{}$ Unfortunately, the coalescence probability is also suppressed by two powers of the ratio of the width to the mass of the B meson, and is therefore many orders of magnitude too small to be observed in current experiments at B factories.

A simple argument based on an SU(3) gauged horizontal symmetry is presented in detail that connects the explanation for three generations of matter with the existence of a triplet of right-handed neutrinos. This rationale for right-handed neutrinos is analogous to, but completely independent of, grand unification. A supersymmetric model with a gauged horizontal SU(3) removes the dangerous dimension-5 Planck-suppressed operators that lead to too fast proton decay in ordinary supersymmetric models. The most direct test of this idea is the observation of lepton flavor violating interactions arising from the exchange of SU(3) gauge bosons.

In reply to the criticism made by Mielke in the preceding Comment on our recent paper, we once again explicitly demonstrate the inconsistency of the coupling of a Dirac field to gravitation in the teleparallel equivalent of general relativity. Moreover, we stress that the mentioned inconsistency is generic for all sources with spin and is by no means restricted to the Dirac field. In this sense the $\mathrm{SL}(4,R)\mathrm{}$-covariant generalization of the spinor fields in the teleparallel gravity theory is irrelevant to the inconsistency problem.

Contrary to the claim in a recent publication [Phys. Rev. D 67, 044016 (2003)], I explicitly demonstrate the consistency of the coupling of Dirac fields to the teleparallelism equivalent of general relativity. Moreover, it is pointed out that, in a metric-affine framework, a $\mathrm{SL}(4,R)\mathrm{}$-covariant generalization of the Dirac equation needs to be considered.

To build genuine generators of the rotations group in noncommutative quantum mechanics, we show that it is necessary to extend the noncommutative parameter $\theta$ to a field operator, which proves to be only momentum dependent. We find consequently that this field must be obligatorily a dual Dirac monopole in momentum space. Recent experiments in the context of the anomalous Hall effect provide evidence for a monopole in the crystal momentum space. We suggest a connection between the noncommutative field and the Berry curvature in momentum space which is at the origin of the anomalous Hall effect.