Lepton distribution as a probe of new physics in production and decay of the t quark and its polarization

We investigate the possibilities of studying new physics in various processes of t-quark production using kinematical distributions of the secondary lepton coming from decay of t quarks. We show that the angular distributions of the secondary lepton are insensitive to the anomalous tbW vertex and hence are pure probes of new physics in a generic process of t-quark production. The energy distribution of the lepton is distinctly affected by anomalous tbW couplings and can be used to analyze them independent of the production process of t quarks. The effects of t polarization on the distributions of the decay lepton are demonstrated for top-pair production process at a gamma-gamma collider mediated by a heavy Higgs boson.Comment: 15 pages, 7 figures, uses axodraw.sty (included), references added. v3 to appear in Journal of High Energy Physics. Incorporates minor changes in the discussion on radiative corrections which do not affect the results. Typo in reference correcte

Systematic study of autocorrelation time in pure SU(3) lattice gauge theory

Results of our autocorrelation measurement performed on Fujitsu AP1000 are reported. We analyze (i) typical autocorrelation time, (ii) optimal mixing ratio between overrelaxation and pseudo-heatbath and (iii) critical behavior of autocorrelation time around cross-over region with high statistic in wide range of $\beta$ for pure SU(3) lattice gauge theory on $8^4$, $16^4$ and $32^4$ lattices. For the mixing ratio K, small value (3-7) looks optimal in the confined region, and reduces the integrated autocorrelation time by a factor 2-4 compared to the pseudo-heatbath. On the other hand in the deconfined phase, correlation times are short, and overrelaxation does not seem to matter For a fixed value of K(=9 in this paper), the dynamical exponent of overrelaxation is consistent with 2 Autocorrelation measurement of the topological charge on $32^3 \times 64$ lattice at $\beta$ = 6.0 is also briefly mentioned.Comment: 3 pages of A4 format including 7-figure

Autocorrelation in Updating Pure SU(3) Lattice Gauge Theory by the use of Overrelaxed Algorithms

We measure the sweep-to-sweep autocorrelations of blocked loops below and above the deconfinement transition for SU(3) on a $16^4$ lattice using 20000-140000 Monte-Carlo updating sweeps. A divergence of the autocorrelation time toward the critical $\beta$ is seen at high blocking levels. The peak is near $\beta$ = 6.33 where we observe 440 $\pm$ 210 for the autocorrelation time of $1\times 1$ Wilson loop on $2^4$ blocked lattice. The mixing of 7 Brown-Woch overrelaxation steps followed by one pseudo-heat-bath step appears optimal to reduce the autocorrelation time below the critical $\beta$. Above the critical $\beta$, however, no clear difference between these two algorithms can be seen and the system decorrelates rather fast.Comment: 4 pages of A4 format including 6-figure

Full order alpha electroweak corrections to double Higgs-strahlung at the linear collider

We present the full order alpha electroweak radiative corrections to the double Higgs-strahlung process e+e- --> ZHH. The computation is performed with the help of GRACE-loop. After subtraction of the initial state QED radiative corrections, we find that the genuine weak corrections in the $\alpha$-scheme are small for Higgs masses and energies where this cross section is largest and is most likely to be studied. These corrections decrease with increasing energies attaining about $\sim -10$ at $\sqrt{s}=1.5$TeV. The full order alpha correction on the other hand is quite large at threshold but small at energies around the peak. We also study changes in the shape of the invariant mass of the Higgs pair which has been shown to be a good discriminating variable for the measurement of the triple Higgs vertex in this reaction.Comment: 18 pages, 5 figures and 3 table

Particle Collisions on Stringy Black Hole Background

The collision of two particles in the background of a Sen black hole is studied. With the equations of motion of the particles, the center-of-mass energy is investigated when the collision takes place at the horizon of a Sen black hole. For an extremal Sen black hole, we find that the center-of-mass energy will be arbitrarily high with two conditions: (1) spin $a\neq 0$ and (2) one of the colliding particles has the critical angular momentum $l_{\text{c}}=2$. For a nonextremal Sen black hole, we show that, in order to obtain an unlimited center-of-mass energy, one of the colliding particles should have the critical angular momentum $l'_{\text{c}}=2 r_{+}/a$ ($r_{+}$ is the radius of the outer horizon for a nonextremal black hole). However, a particle with the angular momentum $l=l'_{\text{c}}$ could not approach the black hole from outside of the horizon through free fall, which implies that the collision with arbitrarily high center-of-mass energy could not take place. Thus, there is an upper bound of the center-of-mass energy for the nonextremal black hole. We also obtain the maximal center-of-mass energy for a near-extremal black hole and the result implies that the Planck-scale energy is hard to be approached. Furthermore, we also consider the back-reaction effects. The result shows that, neglecting the gravitational radiation, it has a weak effect on the center-of-mass energy. However, we argue that the maximum allowed center-of-mass energy will be greatly reduced to below the Planck-scale when the gravitational radiation is included.Comment: 17 pages, 4 figures, published versio

Scaling and confinement aspects of tadpole improved SU(2) lattice gauge theory and its abelian projection

Using a tadpole improved SU(2) gluodynamics action, the nonabelian potential and the abelian potential after the abelian projection are computed. Rotational invariance is found restored at coarse lattices both in the nonabelian theory and in the effective abelian theory resulting from maximal abelian projection. Asymptotic scaling is tested for the SU(2) string tension. Deviation of the order of $6$ is found, for lattice spacings between 0.27 and 0.06 fm. Evidence for asymptotic scaling and scaling of the monopole density in maximal abelian projection is also seen, but not at coarse lattices. The scaling behavior is compared with analyses of Wilson action results, using bare and renormalized coupling schemes. Using extended monopoles, evidence is found that the gauge dependence of the abelian projection reflects short distance fluctuations, and may thus disappear at large scales.Comment: 28 pages, RevTeX, 12 figures using epsfig (included); accepted for publication in Physical Revie

Temperature Dependence of Extended and Fractional SU(3) Monopole Currents

We examine in pure SU(3) the dependence of extended monopole current k and cross-species extended monopole current k^{cross} on temperature t, monopole size L, and fractional monopole charge 1/q. We find that features of both k and k^{cross} are sensitive to t for a range of L and q. In particular, the spatial-temporal asymmetry ratios of both k and k^{cross} are sensitive over a range of L and q to the SU(3) deconfinement transition. The motivation for studying cross, extended, and fractional monopoles in SU(3) is given.Comment: 15 pages (archiving final publication version; very minor revisions

Abelian Dominance of Chiral Symmetry Breaking in Lattice QCD

Calculations of the chiral condensate on the lattice using staggered fermions and the Lanczos algorithm are presented. Four gauge fields are considered: the quenched non-Abelian field, an Abelian projected field, and monopole and photon fields further decomposed from the Abelian field. Abelian projection is performed in maximal Abelian gauge and in Polyakov gauge. The results show that monopoles in maximal Abelian gauge largely reproduce the chiral condensate values of the full non-Abelian theory, in both SU(2) and SU(3) color.Comment: 13 pages in RevTex including 6 figures, uucompressed, self-extractin

Search for anomalous top-gluon couplings at LHC revisited

Through top-quark pair productions at LHC, we study possible effects of nonstandard top-gluon couplings yielded by SU(3)xSU(2)xU(1) invariant dimension-6 effective operators. We calculate the total cross section and also some distributions for p p -> t tbar X as functions of two anomalous-coupling parameters, i.e., the chromoelectric and chromomagnetic moments of the top, which are constrained by the total cross section sigma(p pbar -> t tbar X) measured at Tevatron. We find that LHC might give us some chances to observe sizable effects induced by those new couplings.Comment: One comment and related two refs. added. Final version (to appear in Eur.Phys.J. C