We propose and study an improved method to calculate the fermionic determinant of dynamical configurations. The evaluation or at least stochastic estimation of the ratios of fermionic determinants is essential for a recently proposed updating method of smeared link dynamical fermions. This update creates a sequence of configurations by changing a subset of the gauge links by a pure gauge heat bath or over-relaxation step. The acceptance of the proposed configuration depends on the ratio of the fermionic determinants on the new and original configurations. We study this ratio as a function of the number of links that are changed in the heat bath update. We find that even when every link of a given direction and parity of a $10\hspace{0.5em}{\mathrm{fm}}^4$ configuration is updated, the average of the determinant ratio is still close to one and with the improved stochastic estimator the proposed change is accepted with about 20% probability. This improvement suggests that the new updating technique can be efficient even on large lattices and could provide an updating method for dynamical overlap actions.

We show that the lattice calculation of $\overrightarrow{K}\pi \pi$ and ${\epsilon }^{\prime }/\epsilon$ amplitudes for (8,1) and (27,1) operators to ${O(p}^4)$ in chiral perturbation theory is feasible when one uses $\overrightarrow{K}\pi \pi$ computations at the two unphysical kinematics allowed by the Maiani-Testa theorem, along with the usual (computable) two- and three-point functions, namely $\overrightarrow{K}0,$ $\overrightarrow{K}\pi$ (with momentum), and $K-\overline{K}.$ Explicit expressions for the finite logarithms emerging from our ${O(p}^4)$ analysis to the above amplitudes are also given.

We study the dipole picture for the description of deep inelastic scattering, focusing on the structure functions which are driven directly by the gluon distribution. One performs estimates using the effective dipole cross section given by the Glauber-Mueller approach in QCD, which encodes the corrections due to the unitarity effects associated with the saturation phenomenon. We also address issues about frame invariance of the calculations when analyzing the observables.

We investigate twist-3 effects in the polarized virtual photon structure. The structure functions $g_1^{\gamma }$ and $g_2^{\gamma }$ of a polarized photon could be experimentally studied in future polarized ep or $e^{+}{e}^{-}$ colliders. The leading contributions to $g_1^{\gamma }$ are twist-2 effects, while another structure function $g_2^{\gamma },$ which exists only for the virtual photon target, receives not only twist-2 but also twist-3 contributions. We first show that twist-3 effects actually exist in the box-diagram contributions and we extract the twist-3 part, which can also be reproduced by the pure QED operator product expansion. We then calculate the nontrivial lowest moment $\mathrm{}(n=3\mathrm{})\mathrm{}$ of the twist-3 contribution to $g_2^{\gamma }$ in QCD. For large $N_c$ (the number of colors), the QCD analysis of twist-3 effects in the flavor nonsinglet part of $g_2^{\gamma }$ becomes tractable and we can obtain its moments in a compact form for all n.

In this paper we try to extract the Cabibbo-Kobayashi-Maskawa angle $\gamma$ from the new “mixed” system of $B^{+}\to {\pi }^{+}{K}^0$ and $B_d^0\to {\pi }^0{K}^0$ decays. We also update the constraints on the angle $\gamma$ from the observables R and $A_0.$ In the parametrization, the SU(2) isospin symmetry of strong interactions is applied. We find the following results: (a) the measured value of R is now very close to unity, the bound on the angle $\gamma$ from the measurement of R is therefore not as promising as before, but some bounds on $\gamma$ can still be read off from the $r-\gamma$ plane if r could be fixed by using an additional input; (b) the measured $R_1$ implies a limit on the strong phase ${\Delta }_1$; (c) due to the contribution from the color allowed electroweak penguin amplitude, the minimal value of $R_1$ can be larger than unity. For ${\epsilon }_1=0.2\mathrm{}$ and $R_1=1.2,$ the range of $65°<~\gamma <~115°$ will be excluded, such bounds on $\gamma$ are interesting and complimentary to the limits from global fit; and (d) the dependences of extraction of $\gamma$ on the variation of parameters ${\epsilon }_1,$ $\rho ,$ and $r_1$ and strong phases are also studied.

We estimate in this paper the errors in the zenith angle distribution for the charged current events of the solar neutrinos caused by the uncertainty of Earth’s electron density. In the model of the Preliminary Reference Earth Model with a $5\%$ uncertainty in the Earth’s electron density we numerically calculate the corrections to the correlation between $[N{]}_5/[N{]}_2$ and $[N{]}_2/[N{]}_3,$ and find the errors notable.

Current neutrino oscillation data indicate that the $3\times 3$ lepton flavor mixing matrix V is likely to be symmetric about its $V_{e3\mathrm{}}-V_{\mu 2}-V_{\tau 1}$ axis. This off-diagonal symmetry corresponds to three pairs of congruent unitarity triangles in the complex plane. Terrestrial matter effects can substantially modify the genuine CP-violating parameter and off-diagonal asymmetries of V in realistic long-baseline experiments of neutrino oscillations.

Despite the fact that the solar neutrino flux is now well understood in the context of matter-affected neutrino mixing, we find that it is not yet possible to set a strong and model-independent bound on solar neutrino decays. If neutrinos decay into truly invisible particles, the Earth-Sun baseline defines a lifetime limit of $\tau /m\gtrsim {10}^{-4}\hspace{0.5em}\mathrm{s}/\mathrm{e}\mathrm{V}.$ However, there are many possibilities which must be excluded before such a bound can be established. There is an obvious degeneracy between the neutrino lifetime and the mixing parameters. More generally, one must also allow the possibility of active daughter neutrinos and/or antineutrinos, which may partially conceal the characteristic features of decay. Many of the most exotic possibilities that presently complicate the extraction of a decay bound will be removed if the KamLAND reactor antineutrino experiment confirms the large-mixing angle solution to the solar neutrino problem and measures the mixing parameters precisely. Better experimental and theoretical constraints on the ${}^8\mathrm{B}$ neutrino flux will also play a key role, as will tighter bounds on absolute neutrino masses. Though the lifetime limit set by the solar flux is weak, it is still the strongest direct limit on nonradiative neutrino decay. Even so, there is no guarantee (by about eight orders of magnitude) that neutrinos from astrophysical sources such as a Galactic supernova or distant active galactic nuclei will not decay.

We reexamine the issue of mixing matrix renormalization in theories that include Dirac or Majorana fermions. We show how a gauge-variant on-shell renormalized mixing matrix can be related to a manifestly gauge-independent one within a generalized $\overline{\mathrm{MS}}$ scheme of renormalization. This scheme-dependent relation is a consequence of the fact that in any scheme of renormalization, the gauge-dependent part of the mixing-matrix counterterm is ultraviolet safe and has a pure dispersive form. Employing the unitarity properties of the theory, we can successfully utilize the aforementioned scheme-dependent relation to preserve basic global or local symmetries of the bare Lagrangian through the entire process of renormalization. As an immediate application of our study, we derive the gauge-independent renormalization-group equations of mixing matrices in a minimal extension of the standard model with isosinglet neutrinos.

We investigate leptogenesis with almost degenerate neutrinos in the framework of the democratic mass matrix, which naturally explains the large mixing angles for neutrino oscillations as well as quark masses and the mixing matrix. We find that the baryon asymmetry in the present universe is explained via the decays of right-handed neutrinos produced nonthermally by the inflaton decay. The model predicts neutrinoless double beta decays accessible in near future experiments.

We consider a collinear effective theory of highly energetic quarks with energy E, interacting with collinear and soft gluons by integrating out collinear degrees of freedom to subleading order. The collinear effective theory offers a systematic expansion in power series of a small parameter $\lambda \sim p_{\perp }/E,$ where $p_{\perp }$ is the transverse momentum of a collinear particle. We construct the effective Lagrangian to first order in $\lambda$ and discuss its features, including additional symmetries such as collinear gauge invariance and reparametrization invariance. Heavy-light currents can be matched from the full theory onto the operators in the collinear effective theory at one loop and to order $\lambda .$ We obtain heavy-light current operators in the effective theory, calculate their Wilson coefficients at this order, and the renormalization group equations for the Wilson coefficients are solved. As an application, we calculate the form factors for decays of B mesons to light energetic mesons to order $\lambda$ and at leading-logarithmic order in ${\alpha }_s.$

Positivity constraints are derived for the generalized parton distributions (GPDs) of spin-1/2 hadrons. The analysis covers the full set of eight twist-2 GPDs. Several new inequalities are obtained which constrain GPDs by various combinations of usual (forward) unpolarized and polarized parton distributions, including the transversity distribution.

Following a previous description of $\Lambda$ and $\overline{\Lambda }$ polarization in unpolarized p-p interactions, within a perturbative QCD factorization scheme with new polarizing fragmentation functions, here we investigate the transverse polarization of Λ’s and $\overline{\Lambda }’\mathrm{s}$ produced in semi-inclusive DIS. Analytical expressions for both neutral and charged current exchange are given. Since quantitative predictions cannot be given at this stage and the comparison with existing data is not yet significant, we present the general formalism and a qualitative analysis displaying generic features of the Λ and $\overline{\Lambda }$ polarization for specific scenarios. Different kinematical situations are considered, corresponding to experiments currently able to study Λ production in semi-inclusive DIS.

We reexamine the time-dependent rates of $B_s\mathrm{}\left(t\right)\mathrm{}\to K^{+}{K}^{-}$ and $B_s\mathrm{}\left(t\right)\mathrm{}\to K^{+}{K}^{-},$ including a lifetime difference between neutral $B_s$ mass eigenstates. The two rates, normalized by the rate of $B_s\to K^0{K}^0,$ are used to obtain ambiguity-free information on a strong phase and on the weak phase γ. We discuss the sensitivity of extracting γ to the measured quantities, and find that an error of $\pm 10°$ in γ is possible for a sample of several thousand $B_s\mathrm{}\left(t\right)\mathrm{}\to K^{+}{K}^{-}$ decays. This study is complementary to a recent similar analysis of the U-spin related decays $B^0\mathrm{}\left(t\right)\mathrm{}\to {\pi }^{+}{\pi }^{-}$ and $B^0\mathrm{}\left(t\right)\mathrm{}\to {\pi }^{+}{\pi }^{-}.$

We have measured the cross sections $d^2\sigma {/dP}_{T}d\eta$ for production of isolated direct photons in $p\overline{p}$ collisions at two different center-of-mass energies, 1.8 TeV and 0.63 TeV, using the Collider Detector at Fermilab. The normalization of both data sets agrees with the predictions of quantum chromodynamics for a photon transverse momentum ${(P}_T)$ of 25 GeV/c, but the shapes versus photon $P_T$ do not. These shape differences lead to a significant disagreement in the ratio of cross sections in the scaling variable $x_T(\equiv {2P}_T/\sqrt{s}).\mathrm{}$ This disagreement in the $x_T$ ratio is difficult to explain with conventional theoretical uncertainties such as scale dependence and parton distribution parametrizations.

We study the collective quark excitations in an extremely anisotropic system of two interpenetrating streams of the quark-gluon plasma. In contrast with the gluon modes, all quark ones appear to be stable in such a system. Even more, the quark modes in the two-stream system are very similar to those in the isotropic plasma.

The behavior of the electron propagator near the mass shell is quite different in three regimes: zero temperature; low temperature, $T\ll m;$ and high temperature, $T\gg m.\mathrm{}$ A unified explanation of the behavior in all three regimes is given in terms of the space-time dependence of the photon propagator along the trajectory $\overrightarrow{r}=\overrightarrow{v}t,$ as $\overrightarrow{t}\infty ,$ where $\overrightarrow{v}$ is the appropriate group velocity of the electron.

We investigate in detail the effects of R-parity lepton number violation in the minimal supersymmetric standard model (MSSM) on the parent process $p\overrightarrow{p}{e}^{+}{e}^{-}+X$ at the CERN Large Hadron Collider (LHC). The numerical comparisons between the contributions of the R-parity violating effects to the parent process via the Drell-Yan subprocess and the gluon-gluon fusion are made. We find that the R-violating effects on $e^{+}{e}^{-}$ pair production at the LHC could be significant. The results show that the cross section of the $e^{+}{e}^{-}$ pair productions via gluon-gluon collision at the LHC can be of the order of ${10}^2\hspace{0.5em}\mathrm{fb},$ and this subprocess may be competitive with the production mechanism via the Drell-Yan subprocess. We also give quantitatively the analysis of the effects from both the mass of the sneutrino and coupling strength of the R-parity violating interactions.

We investigate the one-loop renormalization-group evolution of extended sectors of Yukawa-type couplings. It is shown that Landau poles, which usually provide the necessary low-energy upper bounds that saturate quickly with increasing initial value conditions, lead in some cases to the opposite behavior: some of the low-energy couplings decrease and become vanishingly small for increasingly large initial conditions. We write down the general criteria for this to happen in typical situations, highlighting a concept of repulsive quasifixed points, and illustrate the case both within a two-Yukawa toy model as well as in the minimal supersymmetric standard model with R-parity violation. In the latter case, we consider the theoretical upper bounds on the various couplings, identifying regimes where ${\lambda }_{\mathrm{kl}3\mathrm{}},{\lambda }_{\mathrm{kkk}}^{\prime },{\lambda }_{3kl}^{″}$ are dynamically suppressed due to the Landau pole. We stress the importance of considering a large number of couplings simultaneously. This leads altogether to a phenomenologically interesting seesaw effect in the magnitudes of the various R-parity violating couplings, complementing and in some cases improving the existing limits.

We study the discovery potential for detecting new neutral heavy Majorana leptons as suggested by some extensions of the standard model in recently proposed electron-proton colliders. Since 1998–1999, the option of an electron-proton collider for the Very Large Hadron Collider at Fermilab operating with a proton booster has been considered. We consider the reaction $e^{-}\overrightarrow{p}{e}^{+}+\mathrm{jets}$ and present estimates for the signal and standard model background including hadronization.