Search

We study leptoproduction of $J/\psi$ at large $Q^2$ within the nonrelativistic QCD (NRQCD) factorization formalism. The cross section is dominated by color-octet terms that are of order $\alpha_s$. The color-singlet term, which is of order $\alpha^2_s$, is shown to be a small contribution to the total cross section. We also calculate the tree diagrams for color-octet production at order $\alpha^2_s$ in a region of phase space where there is no leading color-octet contribution. We find that in this regime the color-singlet contribution dominates. We argue that non-perturbative corrections arising from diffractive leptoproduction, higher twist effects, and higher order terms in the NRQCD velocity expansion should be suppressed as $Q^2$ is increased. Therefore, the color-octet matrix elements $< {\cal O}_8^{\psi}(^1S_0)>$ and $$ can be reliably extracted from this process. Finally, we point out that an experimental measurement of the polarization of leptoproduced $J/\psi$ will provide an excellent test of the NRQCD factorization formalism., Comment: 33 pages latex. 10 figures. Uses revtex, epsf, and rotate macros. This paper is also available via the UW phenomenology archives at http://phenom.physics.wisc.edu/pub/preprints/

We study $J/\Psi$ production at photon-photon colliders, which can be realised with Compton scaterring of laser photons at $e^+e^-$ colliders. We find that the production rate through the color-octet channel is comparable to that through the color-singlet channel. Experimentally the two mechanisms can be studied separately because the processes have different signals., Comment: 9 pages, 3 Postscript figures

We combine the NRQCD formalism for the inclusive color singlet and octet production of charmonium states with the parton and the ACCMM model, respectively, and calculate the momentum distribution in the decay B-->J/psi+X. Neglecting the kinematics of soft gluon radiation, we find that the motion of the b quark in the bound state can account, to a large extent, for the observed spectrum. The parton model gives a satisfactory presentation of the data, provided that the heavy quark momentum distribution is taken to be soft. To be explicit, we obtain epsilon_p=O(0.008-0.012) for the parameter of the Peterson et al. distribution function. The ACCMM model can account for the data more accurately. The preferred Fermi momentum p_F=O(0.57 GeV) is in good agreement with recent studies of the heavy quark's kinetic energy., Comment: revised version to be published in Phys. Rev. D; 27 pages, LaTeX, 7 eps figures, uses a4wide.sty, epsfig.sty and amssymb.sty

We calculate the polarization of ${\ensuremath{\psi}}^{\ensuremath{'}}$ due to $\mathrm{gg}\ensuremath{\rightarrow}Q\overline{Q}{[}^{2S+1}{L}_{J}^{(8)}]g\ensuremath{\rightarrow}{\ensuremath{\psi}}^{(\ensuremath{\lambda})}$ color-octet quarkonia production. We find that at low transverse momenta the ${\ensuremath{\psi}}^{\ensuremath{'}}$ is unpolarized due to the contributions proportional to the $L=S=0$ and $L=S=1$ color-octet matrix elements. As ${p}_{\ensuremath{\perp}}$ increases, the ${\ensuremath{\psi}}^{\ensuremath{'}}$ mesons become $100%$ polarized, as predicted by fragmentation calculations. Polarization due to lowest-order color-singlet production is also considered, which qualitatively has a similar shape to the color-octet production.

The color-octet mechanism for the decay $B\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}X$ is proposed to explain the large branching ratio of $B(B\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}X)\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ recently announced by CLEO. We argue that the inclusive ${\ensuremath{\eta}}^{\ensuremath{'}}$ production in $B$ decays may dominantly come from the Cabibbo-favored $b\ensuremath{\rightarrow}(\overline{c}{c)}_{8}s$ process where the $\overline{c}c$ pair is in a color-octet configuration, and followed by the nonperturbative transition $(\overline{c}{c)}_{8}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}X.$ The color-octet intrinsic charm component in the higher Fock states of ${\ensuremath{\eta}}^{\ensuremath{'}}$ is crucial and is induced by the strong coupling of ${\ensuremath{\eta}}^{\ensuremath{'}}$ to gluons via the QCD axial anomaly.

$J/\ensuremath{\psi}$ production associated with a hard photon in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation, being of a QED nature, is investigated thoroughly in this paper. To show its influence on the observation of the color-octet signature in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation via $J/\ensuremath{\psi}$ inclusive production, the cross sections of $J/\ensuremath{\psi}$ production through different mechanisms at various energies are compared quantitatively by presenting them in figures together. The contribution from the production associated with a hard photon to the inclusive production of $J/\ensuremath{\psi}$ is pointed out to be significant at the concerned energies; thus, the influence of it on the observation of the color-octet signature should be dealt with carefully.

In the light case of the noncommuting extended technicolor model the heavy gauge bosons can have a mass less than or of the order of 1 TeV and hence they could be directly produced at foreseeable colliders. Even below their kinematic production threshold they are expected to produce significant deviations from the standard model (SM) predictions to various distributions of production cross sections and asymmetries that could be measured with high precision at the NLC. In this work we study the latter effects due to the heavy neutral Z{sub H} boson in the process e{sup +}e{sup {minus}}{r_arrow}t{bar t}. We find that even for M{sub Z{sub H}}=1500GeV the deviations from the SM, particularly in {sigma}{sub L} and A{sub LR}, are large enough to be measurable at NLC500. {copyright} {ital 1997} {ital The American Physical Society}

The calculation of D-wave charmonium prodution rates in B meson deacys under the NRQCD factorization formalism is presented. We find that inclusion of the color-octet contributions permits us to detect the D-wave charmonium states in B decays at present experimental facilities. The same amount signals of 2^{--} D-wave state as that of \psi' could be observed at LEP and CESR. We also predict the relative production rates for four D-wave states are \delta^c:\delta^c_1: \delta^c_2:\delta^c_3=2.5:3:5:7, where \delta^c, \delta^c_1, \delta^c_2, \delta^c_3 represent respectively the 2^{-+}, 1^{--}, 2^{--}, 3^{--} states., Comment: 11 pages in LaTex

We compute the flavor-changing neutral current process B{r_arrow}X{sub s}{mu}{sup +}{mu}{sup {minus}} in technicolor with scalars model. We find that the branching ratio can be enhanced relative to that of the standard model by as much as 60{percent}. The full parameter space of the model is consistent with the present CLEO and CDF exclusive limits. However, the viability of the model could soon be tested since the decay signals are expected to be observed in the next few years with the upgraded CLEO detector and in CDF run II. {copyright} {ital 1997} {ital The American Physical Society}

We consider the contributions of new gauge bosons to W{bar t}b coupling in the top-color-assisted multiscale technicolor model. We find that the exchange of the diagonal extended technicolor (ETC) gauge boson has no contribution to W{bar t}b coupling. Using the CERN LEP value of R{sub b}, we calculate the corrections to the CKM matrix element V{sub tb} which arise from the sideways ETC gauge boson and coloron exchange. We find that the {delta}V{sub tb} is significantly large for a certain range of the parameters which might be detected in the Fermilab Tevatron collider{close_quote}s run 3. {copyright} {ital 1997} {ital The American Physical Society}

We study the production and the equilibration of a non-Abelian $q\bar{q}$ plasma in an external chromoelectric field, by solving the Boltzmann equation with the non-Abelian features explicitly incorporated. We consider the gauge group $SU(2)$ and show that the colour degree of freedom has a major and dominant role in the dynamics of the system. It is seen that the assumption of the so called Abelian dominance is not justified. Finally, it is also shown that many of the features of microscopic studies of the system appear naturally in our studies as well., Latex pages 22, figures can be obtained from authors. Submitted to PRD

Polarized heavy quarkonium productions in Z{sup 0} decays are considered. We find that polarizations of the produced quarkonia are independent of that of the parent Z{sup 0} provided that one considers the energy distribution or the total production rate. Produced J/{psi}{close_quote}s via the color-octet and the color-singlet mechanisms are expected to be 19{percent} and 29{percent} longitudinally polarized, respectively. The energy dependence of {eta}{sub 1,8}(x) {equivalent_to}d{Gamma}{sub 1,8}{sup L}/dx/d{Gamma}{sub 1,8}/dx is very sensitive to the production mechanism, and, therefore, the measurement of {eta}(x){sub expt} will be an independent probe of the color-octet mechanism. {copyright} {ital 1997} {ital The American Physical Society}

The associated production of a J/{psi} and a photon in photon-hadron collisions is considered and shown to be a good probe of the presence of color-octet-mediated channels in quarkonia production, as predicted by the factorization approach within NRQCD. Total and differential cross sections for photoproduction at fixed target experiments and at DESY HERA are presented. Associated J/{psi}+{gamma} production at hadron colliders is briefly discussed. {copyright} {ital 1997} {ital The American Physical Society}

We present the nonrelativistic QCD (NRQCD) prediction for the polarization of the J/{psi} promptly produced in b{r_arrow}J/{psi}+X, as well as the helicity-summed production rate. We propose that these observables can be of avail in measuring the three most important color-octet NRQCD matrix elements involved in J/{psi} production. Anticipating the measurement of the polarization parameter {alpha}, we determine its expected range given current experimental bounds on the color-octet matrix elements. We find that the leading-order NRQCD prediction for the polarization parameter {alpha} is expected to lie in the range {minus}0.33 to 0.05 whereas the color-singlet model prediction is {minus}0.40{plus_minus}0.04. {copyright} {ital 1997} {ital The American Physical Society}

We present the x{sub F} and p{sub T} differential cross sections of J/{psi} and {psi}{sup {prime}}, respectively, in the ranges {minus}0.05{lt}x{sub F}{lt}0.25 and p{sub T}{lt}3.5 GeV/c. The data samples are constituted by about 12000 J/{psi} and 200 {psi}{sup {prime}} produced in proton-silicon interactions at 800 GeV/c and decaying into opposite sign muons. The x{sub F} and p{sub T} distributions are compared with recent results from experiments E789 at the same energy and to leading order QCD predictions using the MRS D0 parametrization for the parton structure function. The measured shapes of the differential cross sections, except for the d{sigma}/dx{sub F} at small x{sub F}, agree very well with the prediction, even though their value is quite a bit larger than the prediction. We also present the cos{theta} differential cross section of the J/{psi} which indicates unpolarized production in contrast with color octet models predictions. {copyright} {ital 1997} {ital The American Physical Society}

The direct production rates of D-wave charmonia in the decays of Z{sup 0} are evaluated. The color-octet production processes Z{sup 0}{r_arrow}{sup 3}D{sub J}(c{bar c})q{bar q} are shown to have distinctively large branching ratios as compared with other D-wave charmonium production mechanisms under a proper assumption. This may suggest a crucial channel to test the color-octet mechanism as well as to observe the D-wave charmonium states in Z{sup 0} decays. In addition, a signal for the {sup 3}D{sub J} charmonium states with a large transverse momentum at the Fermilab Tevatron should be observed. {copyright} {ital 1997} {ital The American Physical Society}

We study J/{psi} production at fixed-target energies, including the color-octet production mechanisms predicted by NRQCD. In an earlier paper, we found that the octet components were crucial in understanding p{sub T}-integrated forward (x{sub F}{gt}0) cross sections. Here we make a detailed comparison of the theoretical predictions with measured x{sub F} distributions from fixed-target experiments. We find that the model predictions agree well with data. Taking into account higher orders in NRQCD, we argue that {sigma}({chi}{sub 1})/{sigma}({chi}{sub 2})=0.6, in excellent agreement with data. Similiar arguments also predict that {sigma}({chi})/{sigma}(J/{psi}) is roughly equal in photo- and hadroproduction. {copyright} {ital 1997} {ital The American Physical Society}

We consider the production of pairs of ${B}_{c}$ and ${B}_{c}^{*}$ mesons via gluon-gluon and photon-photon fusion processes in the framework of the nonrelativistic color singlet model and perturbative chromodynamics. We calculate the corresponding cross sections for pp and \ensuremath{\gamma}\ensuremath{\gamma} collisions at the energies of present and future colliders and discuss the characteristics of the production mechanisms. We analyze the uncertainties of theoretical estimations.

The spatial distribution of the action and energy in the color fields of flux tubes is studied in lattice SU(2) field theory for static quarks at separations up to 1 fm. Special attention is paid to the structure of the color fields associated with an excited flux tube with E{sub u} symmetry. We compare our results with hadronic string and flux-tube models. Sum rules are used to extract generalized {beta} functions, to describe the expected color field behavior, and to cross-check the methods used. {copyright} {ital 1997} {ital The American Physical Society}

In the framework of a newly developed factorization formalism which is based on NRQCD, explicit cancellations are shown for the infrared divergences that appeared in the previously calculated hadronic annihilation decay rates of P-wave and D-wave heavy quarkonia. We extend them to a more general case that to leading order in $v^2$ and next-to-leading order in $\alpha_s$, the infrared divergences in the annihilation amplitudes of color-singlet $Q\bar{Q}(^{2S+1}L_J)$ pair can be removed by including the contributions of color-octet operators $Q\bar{Q}(^{2S+1}(L-1)_{J'})$, $Q\bar{Q}(^{2S+1}(L-3)_{J''})$, ... in NRQCD. We also give the decay widths of $^3D_J\rightarrow LH$ at leading order in $\alpha_s$., Comment: 8 pages, LaTex(3 figures included), to be published

Several distinct color flow topologies are possible in multiparton configurations. A method is proposed to find the correct topology, based on a minimization of the total transverse momentum of produced particles. This method is studied for three-jet [Formula presented] and four-jet [Formula presented] events. It is shown how the basic picture is smeared, especially by parton-shower activity. The method, therefore, may not be sufficient on its own, but could still be a useful complement to others, and, e.g., help provide some handle on color rearrangement effects.

The purely electroweak process $qq\to qqZ$ (via $t$-channel $\gamma/Z$ or $W$ exchange) provides a copious and fairly clean source of color-singlet exchange events in $pp$ collisions at the LHC. A judicious choice of phase-space region allows the suppression of QCD backgrounds to the level of the signal. The color-singlet-exchange signal can be distinguished from QCD backgrounds by the radiation patterns of additional minijets in individual events. A rapidity-gap trigger at the minijet level substantially enhances the signal versus the background. Analogous features of weak boson scattering events make $Z+2$-jet events at the LHC an ideal laboratory for investigation of the soft-jet activity expected in weak-boson scattering events., Comment: 24 pages (with 7 embedded figures), Revtex, uses epsf.sty. Z-compressed postscript version also available at http://phenom.physics.wisc.edu/pub/preprints/1996/madph-96-943.ps.Z or at ftp://phenom.physics.wisc.edu/pub/preprints/1996/madph-96-943.ps.Z

It is suggested that virtual gluon-clusters exist in nucleon, and that such colorless and colored objects manifest themselves in the small $x_B$ region of inelastic lepton-nucleon scattering processes. The relationship between the space-time properties of such clusters and the striking features observed in these scattering processes is discussed. A phase-space model is used to show how quantitative results can be obtained in such an approach. The results of this model-calculation are in reasonable agreement with the existing data. Further experiments are suggested., Comment: to be published in Phys. Rev. D

In a previous article, it was proved in the framework of the chiral soliton model that the same Isgur-Wise form factor describes the semileptonic {Lambda}{sub {ital b}}{r_arrow}{Lambda}{sub {ital c}} and {Sigma}{sub {ital b}}{sup ({asterisk})}{r_arrow}{Sigma}{sub {ital c}}{sup ({asterisk})} decays in the large {ital N}{sub {ital c}} limit. It is shown here that this result is in fact independent of the chiral soliton model and is solely the consequence of the spin-flavor SU(4) symmetry which arises in the baryon sector in the large {ital N}{sub {ital c}} limit. {copyright} {ital 1996 The American Physical Society.}

We calculate the lowest order hadronic cross sections for producing colored heavy quark-antiquark pairs in $L=S=0$ and $L=S=1$ configurations. Such $Q\Qbar[{}^1S_0^{(8)}]$ and $Q\Qbar[{}^3P_J^{(8)}]$ states hadronize into $\psi_\Q$ quarkonia at the same order in the NRQCD velocity expansion as previously considered $Q\Qbar[{}^3S_1^{(8)}]$ pairs. Their contributions to prompt Psi and Upsilon production at the Tevatron bring the shapes of theoretical transverse momentum distributions into line with recent CDF measurements. We find that the best fit values for the linear combinations of $Q\Qbar[{}^1S_0^{(8)}]$ and $Q\Qbar[{}^3P_J^{(8)}]$ long distance matrix elements which can be extracted from the data are generally consistent with NRQCD scaling rules., Comment: 27 pages, harvmac, 9 uuencoded figures. Section in original version of this article which discussed quarkonia spin alignment has been removed

We show that the present limit on the inclusive decay {ital b}{r_arrow}{ital s}{gamma} provides strong constraints on technicolor models. In particular, small values of {ital F}{sub {pi}} and the mass of charged octet and singlet technipions are excluded, assuming the most natural form of the technipion coupling to the ordinary quarks. {copyright} {ital 1996 The American Physical Society.}

We study the potential of {ital B}{r_arrow}{ital K}{sup (*)}{ital l}{sup +}{ital l}{sup {minus}} decays as tests of the standard model. After discussing the reliability of theoretical predictions for the hadronic mix elements involved, we examine the impact of different new physics scenarios on various observables. We show that the angular information in {ital B}{r_arrow}{ital K}{sup *}{ital l}{sup +}{ital l}{sup {minus}} together with the dilepton mass distribution can highly constrain new physics. This is particularly true in the large dilepton mass region, where reliable predictions for the hadronic matrix elements can be made with presently available data. As illustrative examples, we compare the standard model predictions with those of two-Higgs-doublet models as well as top-quark color models, all of which give distinct signals in this region.

We consider a model in which each family transforms under a different SU(3) color group. The low-energy effective theory is an extension of the standard model, with additional color octet gauge bosons {ital G}{sub {ital H}} with mass {ital M} that couple preferentially to the third-family quarks. We show that there are two distinct regions of the model`s parameter space in which we can simultaneously evade all the current experimental constraints: one with {ital M}{approx}250 GeV and the other with {ital M}{approx_gt}600 GeV. Within each allowed region we can obtain a correction to the {ital Zb{bar b}} vertex that is consistent with the slightly high value of {ital R}{sub {ital b}} observed at CERN LEP. We show that there are {Delta}{ital B}=1 operators in our model that can suppress the {ital B}-meson semileptonic branching ratio {ital B}{sub sl} and the charm multiplicity per decay {ital n}{sub {ital c}} by enough to reconcile the spectator parton model predictions with the experimental data. In the nonsupersymmetric version of our model we can only obtain the desired corrections to {ital R}{sub {ital b}}, {ital B}{sub sl}, and {ital n}{sub {ital c}} in different regions of the allowed parameter space, while in the supersymmetric more » version we can obtain all three corrections simultaneously. We also discuss a strong-coupling limit of our model in which the third-family quarks become composite. « less

If electroweak symmetry is spontaneously broken by technicolor, there will be technimesons analogous to the mesons of the ordinary strong interactions. One of the lightest technimesons is the technieta $\eta'_T$ (the analogue of the~$\eta'$). In this work we consider the possibility of observing it at a linear $e^+e^-$ collider operating in the $\gamma\gamma$ mode. Detecting the process $\gamma\gamma\rightarrow\eta'_T$ allows for the measurement of the $\eta'_T\gamma\gamma$ anomalous coupling which is in principle sensitive to the underlying technifermion substructure., Comment: 17 pages, revtex, no figures

The non-Abelian analogue of the Landau-Pomeranchuk-Migdal effect is investigated in perturbative QCD. Extending our previous studies, the suppression of induced soft bremsstrahlung due to multiple scatterings of quarks in the spinor representation is considered. The effective formation time of gluon radiation due to the color interference is shown to depend on the color representation of the emitting parton, and an improved formula for the radiative energy loss is derived that interpolates between the factorization and Bethe-Heitler limits.

High energy scattering in (2+1)-dimensional QCD is studied using the recent approach of Verlinde and Verlinde. We calculate the color singlet part of the quark-quark scattering exactly within this approach, and discuss some physical implication of this result. We also demonstrate, by two independent methods, that Reggeization fails for the color octet channel. We briefly comment on the problem in (3+1)-dimensional QCD.

Composite color-octet isodoublet scalar bosons appear in a natural extension of the minimal dynamical symmetry-breaking model. Two important parameters of this model, namely, the mass of the bosons and their Yukawa coupling with the top quark, can be constrained through the present data on ${B}_{d}\ensuremath{-}{\overline{B}}_{d}$ mixing and the $\ensuremath{\epsilon}$ parameters, but the contribution of the new physics to $K\ensuremath{-}\overline{K}$ mixing is shown to be small. We also find that a fairly large region of parameter space is available for this model to be feasible.

Within the framework of pertubative QCD we calculate inclusive [ital J]/[psi] production using the color singlet model.'' Predictions for the total cross section including the leading corrections from initial state radiation and the [psi][prime] contribution are given. We analyze the production and decay properties by considering suitable lepton-hadron correlations. It is shown that the production and the decay process of a [ital J]/[psi] are described by four structure functions, respectively. We give analytical expressions for these structure functions and suggest energy-dependent coefficients of angular distributions as a test for the model. Finally we give detailed predictions for an energy of 10.5 GeV that could be tested at the CLEO-II experiment. The effect of arbitrarily polarized electron and/or positron beams is included.

The recent Tevatron measurement of the forward-backward asymmetry of the top quark shows an intriguing discrepancy with Standard Model expectations, particularly at large t t invariant masses. Measurements of this quantity are subtle at the LHC, due to its pp initial state, however, one can dene a forward-central-charge asymmetry which captures the physics. We study the capability of the LHC to measure this asymmetry and nd that within the SM a measurement at the 5 level

The recent results in $\sqrt{s}=2.76\text{ }\text{ }\mathrm{TeV}$ $\mathrm{Pb}+\mathrm{Pb}$ collisions at the Large Hadron Collider (LHC) reported by the ALICE collaboration shows that the power-law energy-dependence of charged hadron multiplicity in $\mathrm{Pb}+\mathrm{Pb}$ collisions is significantly different from $\mathrm{p}+\mathrm{p}$ collisions. We show that this different energy-dependence can be explained by inclusion of a strong angular-ordering in the gluon-decay cascade within the color glass condensate (or gluon saturation) approach. This effect is more important in nucleus-nucleus collisions where the saturation scale is larger than 1 GeV. Our prescription gives a good description of the LHC data both in $\mathrm{p}+\mathrm{p}$ and $\mathrm{Pb}+\mathrm{Pb}$ collisions.

We present the first measurement of the color representation of the hadronically decaying W boson in t-tbar events, from 5.3 fb^-1 of integrated luminosity collected with the D0 experiment. A novel calorimeter-based vectorial variable, "jet pull," is used, sensitive to the color-flow structure of the final state. We find that the fraction of uncolored W bosons is 0.56 +- 0.42(stat+syst), in agreement with the standard model.

The Wilson coefficients for all 4-parton operators which arise in matching QCD to soft-collinear effective theory (SCET) are computed at 1-loop. Any dijet observable calculated in SCET beyond leading order will require these results. The Wilson coefficients are separated by spin and color, although most applications will involve only the spin-averaged hard functions. The anomalous dimensions for the Wilson coefficients are given to 2-loop order, and the renormalization group equations are solved explicitly. This will allow for analytical resummation of dijet observables to next-to-next-to-leading logarithmic accuracy. For each channel, there is a natural basis in which the evolution is diagonal in color space. The same basis also diagonalizes the color evolution for the soft function. Even though soft functions required for SCET calculations are observable dependent, it is shown that their renormalization group evolution is almost completely determined by a universal structure. With these results, it will be possible to calculate hadronic event shapes or other dijet observables to next-to-leading order with next-to-next-to-leading log resummation.

We use gauge/string duality to investigate the free energy of two static color sources (a heavy quark-antiquark pair) in a Yang-Mills theory in strongly interacting matter, varying temperature and chemical potential. The dual space geometry is Anti-de Sitter with a charged black-hole to describe finite temperature and density in the boundary theory, and we also include a background dilaton field to generate confinement. The resulting phase diagram in the chemical potential-temperature $\mu-T$ plane is in a quite good agreement with lattice results and effective models of QCD., Comment: 4 pages, 5 figures, version published on PRD

Pure SU(3) glue theories exhibit a deconfining phase transition at a nonzero temperature, Tc. Using lattice measurements of the pressure, we develop a simple matrix model to describe the transition region, when T > Tc. This model, which involves three parameters, is used to compute the behavior of the 't Hooft loop. There is a Higgs phase in this region, where off diagonal color modes are heavy, and diagonal modes are light. Lattice measurements of the latter suggests that the transition region is narrow, extending only to about 1.2 Tc. This is in stark contrast to lattice measurements of the renormalized Polyakov loop, which indicates a much wider width. The possible implications for the differences in heavy ion collisions between RHIC and the LHC are discussed., v2: Minor changes in wording, references added

We determine the [ital q[bar q]] pair creation probability in the color flux tube model including effects of non-Abelian interactions in the theory. It is suggested that the color field should be time dependent due to non-Abelian interactions and hence should oscillate with a characteristic collective frequency [omega][sub 0], which depends on the field strength. Our results show that in [ital p]-[ital p] and [ital A]-[ital A] collisions, either the perturbative estimate ([omega][sub 0][much gt][ital m]) or multigluon ionization ([omega][sub 0][much lt][ital m]) process often gives the dominant contribution to the creation of [ital q[bar q]] pairs.

We calculate the asymmetry parameters $A$, $B$, ${C}_{L,R}$ in the deep-inelastic $e\ensuremath{-}d$ and $e\ensuremath{-}p$ scattering processes in the four effective low-energy models (referred to as $\ensuremath{\chi}$, $\ensuremath{\psi}$, $\ensuremath{\eta}$, and alternative left-right-symmetric models) resulting from the breaking of the superstring-inspired ${\mathrm{E}}_{6}$ model and the $\mathrm{SU}{(5)}_{c}$ model, and compared with those in the standard model. It is seen that $\ensuremath{\chi}$ and $\ensuremath{\eta}$ models can be discriminated through the measurement of $A$ and $B$ parameters while ${C}_{L}$ can differentiate the $\ensuremath{\chi}$ model only from the standard model. However, the alternative left-right-symmetric model and the $\mathrm{SU}{(5)}_{c}$ model cannot be distinguished from the standard model through measurement of $A$, $B$, and ${C}_{L}$ parameters. Interestingly, all the models can be markedly distinguished from the standard model through the measurement of ${C}_{R}$ for values of $y$ in the range $0.38\ensuremath{\le}y\ensuremath{\le}0.42$.

Static quark-antiquark potential encodes important information on the chromodynamical interaction between color charges, and recent lattice results show its very nontrivial behavior near the deconfinement temperature T{sub c}. In this paper we study such potential in the framework of the 'magnetic scenario' for the near T{sub c} QCD plasma, and particularly focus on the linear part (as quantified by its slope, the tension) in the potential as well as the strong splitting between the free energy and internal energy. By using an analytic 'ellipsoidal bag' model, we will quantitatively relate the free energy tension to the magnetic condensate density and relate the internal energy tension to the thermal monopole density. By converting the lattice results for static potential into density for thermal monopoles we find the density to be very large around T{sub c} and indicate at quantum coherence, in good agreement with direct lattice calculation of such density. A few important consequences for heavy ion collisions phenomenology will also be discussed.

We argue that in cold, dense quark matter, in the limit of a large number of colors the ground state is unstable with respect to creation of a complicated Quarkyonic Chiral Spiral (QCS) state, in which both chiral and translational symmetries are spontaneously broken. The entire Fermi surface is covered with patches of QCSs, whose number increases as the quark density does. The low energy excitations are gapless, given by Wess-Zumino-Novikov-Witten model plus transverse kinetic terms localized about different patches., 18 pages, 3 figures

The bulk viscosity in spin-one color-superconducting strange quark matter is calculated by taking into account the interplay between the nonleptonic and semi-leptonic week processes. In agreement with previous studies, it is found that the inclusion of the semi-leptonic processes may result in non-negligible corrections to the bulk viscosity in a narrow window of temperatures. The effect is generally more pronounced for pulsars with longer periods. Compared to the normal phase, however, this effect due to the semi-leptonic processes is less pronounced in spin-one color superconductors. Assuming that the critical temperature of the phase transition is much larger than 40 keV, the main effect of spin-one color superconductivity in a wide range of temperatures is an overall increase of the bulk viscosity with respect to the normal phase. The corresponding enhancement factor reaches up to about 9 in the polar and A-phases, about 25 in the planar phase and about 29 in the CSL phase. This factor is determined by the suppression of the nonleptonic rate in color-superconducting matter and, therefore, may be even larger if all quark quasiparticles happen to be gapped., Comment: 10 pages, 4 multi-panel figures, including one new in the final version

The tetraquark states with diquark-anti-diquark configuration have been studied in the flux-tube model, in which the multibody confinement is used. In this model approach, the states Y(2175), f{sub 0}(600), f{sub 0}(980), and X(1576) can be assigned as tetraquark states. They are color confinement resonances with three-dimension structure. This study suggests that the multibody confinement should be employed in the quark model study of multiquark states instead of the additive two-body confinement.

By using the Britto-Cachazo-Feng-Witten recursion relation of $\mathcal{N}=4$ super Yang-Mills theory, we proved the color reflection, $U(1)$ decoupling, Kleiss-Kuijf and Bern-Carrasco-Johansson relations for color-ordered amplitudes of $\mathcal{N}=4$ super Yang-Mills theory. This proof verified the conjectured Bern-Carrasco-Johansson relations of matter fields. The proof depended only on general properties of superamplitudes. We showed also that the color reflection relation and $U(1)$-decoupling relation are special cases of Kleiss-Kuijf relations.

We consider a model where right-handed neutrinos and sneutrinos are introduced to the minimal supersymmetric standard model. In the scalar potential of this model, there exist trilinear and quartic terms in scalar potential that are proportional to Yukawa couplings of neutrinos. Because of these trilinear and quartic terms, color and/or charge breaking (CCB) and unbounded-from-below (UFB) directions appear along which sneutrinos have a vacuum expectation value, making the vacuum of the electroweak symmetry breaking unstable. We analyze the scalar potential of this model and derive necessary conditions for color and/or charge breaking and unbounded-from-below directions to vanish.

The color neutral two-flavor superconducting phase of cold and dense quark matter is studied in the presence of constant magnetic fields and at moderate baryon densities. In the first part of the paper, a two-flavor effective Nambu\char21{}Jona-Lasinio model consisting of a chiral symmetry breaking ($\ensuremath{\chi}\mathrm{SB}$) mass gap ${\ensuremath{\sigma}}_{B}$, a color superconducting (CSC) mass gap ${\ensuremath{\Delta}}_{B}$ and a color chemical potential ${\ensuremath{\mu}}_{8}$ is introduced in the presence of a rotated $U(1)$ magnetic field $\stackrel{\texttildelow{}}{\mathbf{B}}$. To study the phenomenon of magnetic catalysis in the presence of strong magnetic fields, the gap equations corresponding to ${\ensuremath{\sigma}}_{B}$ and ${\ensuremath{\Delta}}_{B}$, as well as ${\ensuremath{\mu}}_{8}$ are solved in the lowest Landau level approximation. In the second part of the paper, a detailed numerical analysis is performed to explore the effect of any arbitrary magnetic field on the above mass gaps and the color chemical potential. The structure of the $\ensuremath{\chi}\mathrm{SB}$ and CSC phases is also presented in the ${\ensuremath{\mu}}_{c}\mathrm{\text{\ensuremath{-}}}\stackrel{\texttildelow{}}{e}B$ plane, and the effect of ${\ensuremath{\mu}}_{8}$ on the phase structure of the model is explored. As it turns out, whereas the transition from the $\ensuremath{\chi}\mathrm{SB}$ to CSC phase is of first order, nonvanishing ${\ensuremath{\mu}}_{8}$ affects essentially the second order phase transition from CSC to the normal phase.

We report on a measurement of the gamma(1S + 2S + 3S) -> e(+)e(-) cross section at midrapidity in p + p collisions at root s = 200 GeV. We find the cross section to be 114 +/- 38(stat + fit)(-24)(+23)(syst) pb. Perturbative QCD calculations at next-to-leading order in the color evaporation model are in agreement with our measurement, while calculations in the color singlet model underestimate it by 2 sigma. Our result is consistent with the trend seen in world data as a function of the center-of-mass energy of the collision and extends the availability of gamma data to RHIC energies. The dielectron continuum in the invariant-mass range near the gamma is also studied to obtain a combined yield of e(+)e(-) pairs from the sum of the Drell-Yan process and b-(b) over bar production.

At zero density, the `t Hooft large N_c limit often provides some very useful qualitative insights into the non-perturbative physics of QCD. However, it is known that at high densities the `t Hooft large N_c world looks very different from the N_c=3 world, which is believed to be in a color superconducting phase at high densities. At large N_c, on the other hand, the DGR instability causes a chiral-density wave phase to dominate over the color superconducting phase. There is an alternative large N_c limit, with the quarks transforming in the two-index antisymmetric representation of the gauge group, which at N_c=3 reduces to QCD but looks quite different at large N_c. We show that in this alternative large N_c limit, the DGR instability does not occur, so that it may be plausible that the ground state of high-density quark matter is a color superconductor even when N_c is large. This revives the hope that a large N_c approximation might be useful for getting some insights into the high-density phenomenology of QCD., Comment: 8 pages, 1 figure