Search

We propose a new measurement of the heavy flavor hadron double spin asymmetry in deep-inelastic scattering at a future Electron-Ion Collider (EIC) to constrain the polarized gluon distribution function inside the proton. Statistical projection on D0 meson double spin asymmetry is calculated with an EIC central detector using an all-silicon tracker and vertexing subsystem. A first impact study was done by interpreting pseudodata at next-to-leading order in QCD. The sensitivity of the experimental observable in constraining gluon helicity distribution in a wide range of parton momentum fraction x has been investigated considering different collision energies. This measurement complements the inclusive spin-dependent structure function measurement and provides an opportunity to constrain the gluon helicity distribution in the moderate x region.

We apply recent developments in large momentum effective theory (LaMET) to formulate a non-perturbative calculation of the single-transverse spin asymmetry in terms of the quasi transverse-momentum-dependent quark distribution functions from the so-called Sivers mechanism. When the spin asymmetry is defined as the ratio of the quark Sivers function over the spin averaged distribution, it can be directly calculated in terms of the relevant quasi distributions with the soft functions and perturbative matching kernels cancelling out. Apart from the general formula presented, we have verified the result in the small transverse distance limit at one-loop order, which reduces to a collinear expansion at twist-three level., Comment: 12 pages, 6 figures

We study the lepton-jet correlation in deep inelastic scattering. We perform one-loop calculations for the spin averaged and transverse spin dependent differential cross sections depending on the total transverse momentum of the final state lepton and the jet. The transverse momentum dependent (TMD) factorization formalism is applied to describe the relevant observables. To show the physics reach of this process, we perform a phenomenological study for HERA kinematics and comment on an ongoing analysis of experimental data. In addition, we highlight the potential of this process to constrain small-$x$ dynamics., Comment: 10 pages, 5 figures

We present a full evaluation of the deeply virtual Compton scattering (DVCS) cross section in the dipole framework in the small-x region. The result features the $\cos \phi$ and $\cos 2\phi$ azimuthal angular correlations which have been missing in previous studies based on the dipole model. In particular, the $\cos 2\phi$ term is generated by the elliptic gluon Wigner distribution whose measurement at the planned electron-ion collider (EIC) provides an important information about the gluon tomography at small-x. We also show the consistency with the standard collinear factorization approach based on the quark and gluon generalized parton distributions (GPDs)., Comment: 16 pages, 2 figures

We compute the twist-three fragmentation contribution to the transverse single spin asymmetry (SSA) in light hadron production $p^\uparrow p\to hX$ and $p^\uparrow A\to hX$ including the gluon saturation effect in the unpolarized nucleon/nucleus. Together with the results in our previous paper, this completes the full evaluation of the SSA in this process in the "hybrid" formalism. We argue that the dependence of SSAs on the atomic mass number in the forward region can elucidate the relative importance of the soft gluon pole contribution from the twist-three quark-gluon-quark correlation in the polarized nucleon and the twist-three fragmentation contribution from the final state hadron., 11 pages, 2 figures

We compute the transverse single spin asymmetry in light hadron production $p^\uparrow p\to hX$ and $p^\uparrow A\to hX$ including the gluon saturation effect in the unpolarized nucleon/nucleus. In the forward (large-$x_F$) region, the dominant contribution comes from the so-called derivative term associated with the soft gluonic pole. This leads to the cancellation of nuclear effects in $A_N$ which can be tested at RHIC. We also show that the soft fermionic pole disappears in the saturation environment., 13 pages, 2 figures; Revised version, to appear in PRD

We study the transverse momentum resummation for dijet correlation in hadron collisions based on the Collins-Soper-Sterman formalism. The complete one-loop calculations are carried out in the collinear factorization framework for the differential cross sections at low imbalance transverse momentum between the two jets. Important cross checks are performed to demonstrate that the soft divergences cancelled out between different diagrams, and in particular, those associated with final state jets. The leading and sub-leading logarithms are identified. All order resummation is derived following the transverse momentum dependent factorization at this order. Its phenomenological applications are also presented., 51 pages, 10 figures

We revisit the issue of the large negative next-to-leading order (NLO) cross section for single inclusive hadron production in $pA$ collisions in the saturation formalism. By implementing the exact kinematical constraint in the modified dipole splitting functions, two additional positive NLO correction terms are obtained. In the asymptotic large $k_\perp$ limit, we analytically show that these two terms become as large as the negative NLO contributions found in our previous calculation. Furthermore, the numerical results demonstrate that the applicable regime of the saturation formalism can be extended to a larger $k_\perp$ window, where the exact matching between the saturation formalism (in the asymptotic $k_\perp$ regime) and the collinear factorization calculations will have to be performed separately. In addition, after significantly improving the numerical accuracy of the NLO correction, we obtain excellent agreement with the LHC and RHIC data for forward hadron productions., Comment: 20 pages, 7 figures; v2 fixes some typos

We investigate the effect of QCD resummation to kinematical correlations in the Higgs boson plus high transverse momentum (Pt) jet events produced at hadron colliders. We show that at the complete one-loop order, the Collins-Soper-Sterman resummation formalism can be applied to derive the Sudakov form factor, which is found to be independent of jet-finding algorithm. We compare the singular behavior of resummation calculation to fixed order prediction in the case that Higgs boson and high Pt jet are produced nearly back-to-back in their transverse momenta, and find a perfect agreement. The phenomenological importance of the resummation effect at the LHC is also demonstrated., 7 pages, 1 figure

We study the transverse momentum dependent (TMD) parton distributions in the newly proposed quasi-parton distribution function framework in Euclidean space. A soft factor subtraction is found to be essential to make the TMDs calculable on lattice. We show that the quasi-TMDs with the associated soft factor subtraction can be applied in hard QCD scattering processes such as Drell-Yan lepton pair production in hadronic collisions. This allows future lattice calculations to provide information on the non-perturbative inputs and energy evolutions for the TMDs. Extension to the generalized parton distributions and quantum phase space Wigner distributions will lead to a complete nucleon tomography on lattice., Comment: 7 pages, 2 figures

We derive all order soft gluon resummation in dijet azimuthal angular correlation in hadronic collisions at the next-to-leading logarithmic level. The relevant coefficients for the Sudakov resummation factor, the soft and hard factors, are calculated. The theory predictions agree well with the experimental data from D0 Collaboration at the Tevatron. This provides a benchmark calculation for the transverse momentum dependent QCD resummation for jet productions in hadron collisions.

We construct a theoretical framework to match the formulas for forward inclusive hadron productions in p A collisions in the small x saturation formalism and collinear factorization. The small x calculation can be viewed as a power series in Q s 2 / k ⊥ 2 , in which the collinear factorization result corresponds to the leading term. At high transverse momentum, the subleading correction terms are insignificant, whereas at low p ⊥ , the power corrections become important and the small x resummation is essential to describe the differential cross section. We show that the familiar collinear factorization calculation can smoothly match the results from small x factorization at next-to-leading order in α s when we use exact kinematics, as opposed to the approximate kinematics in previous work. With this matching, we can describe the experimental data from the RHIC very well at high p ⊥ .

We examine the QCD evolution for the transverse momentum dependent observables in hard processes of semi-inclusive hadron production in deep inelastic scattering and Drell-Yan lepton pair production in $pp$ collisions, including the spin-average cross sections and Sivers single transverse spin asymmetries. We show that the evolution equations derived by a direct integral of the Collins-Soper-Sterman evolution kernel from low to high $Q$ can describe well the transverse momentum distributions of the unpolarized cross sections in the ${Q}^{2}$ range from 2 to $100\text{ }\text{ }{\mathrm{GeV}}^{2}$. In addition, the matching is established between our evolution and the Collins-Soper-Sterman resummation with ${b}_{*}$ prescription and Konychev-Nodalsky parametrization of the nonperturbative form factors, which are formulated to describe the Drell-Yan lepton pair and $W/Z$ boson production in hadronic collisions. With these results, we present the predictions for the Sivers single transverse spin asymmetries in Drell-Yan lepton pair production and ${W}^{\ifmmode\pm\else\textpm\fi{}}$ boson production in polarized $pp$ and ${\ensuremath{\pi}}^{\ensuremath{-}}p$ collisions for several proposed experiments. We emphasize that these experiments will not only provide crucial test of the sign change of the Sivers asymmetry but also provide important opportunities to study the QCD evolution effects.

We present a calculation for the photoproduction of $\eta_c$ under the framework of NRQCD factorization formalism. We find a quite unique feature that the color-singlet contribution to this process vanishes at not only the leading order but also the next to leading order perturbative QCD calculations and that the dominant contribution comes from the color-octet ${}^1S_0^{(8)}$ subprocess. The nonperturbative color-octet matrix element of ${}^1S_0^{(8)}$ of $\eta_c$ is related to that of ${}^3S_1^{(8)}$ of $J/\psi$ by the heavy quark spin symmetry, and the latter can be determined from the direct production of $J/\psi$ at large transverse momentum at the Fermilib Tevatron. We then conclude that the measurement of this process may clarify the existing conflict between the color-octet prediction and the experimental result on the $J/\psi$ photoprodution.

Within the t-J model, the c-axis charge dynamics of the copper oxide materials in the underdoped and optimally doped regimes is studied by considering the incoherent interlayer hopping. It is shown that the c-axis charge dynamics is mainly governed by the scattering from the in-plane fluctuation. In the optimally doped regime, the c-axis resistivity is a linear in temperatures, and shows the metallic-like behavior for all temperatures, while the c-axis resistivity in the underdoped regime is characterized by a crossover from the high temperature metallic-like behavior to the low temperature semiconducting-like behavior, which are consistent with experiments and numerical simulations., Comment: 6 pages, Latex, Three figures are added

J/psi production in top quark rare decays is investigated under the framework of NRQCD factorization formalism. Various production channels are studied, and we find that the contributions from the color-singlet quark fragmentation and the color-octet gluon fragmentation are both over 3 orders larger than that from the leading order color-singlet process. The numerical results show that the branching ratio B(t -> c + J/psi + X) is about 10^{-14} in the SM, and 10^{-10} in the MSSM., 10 pages, RevTex, 4 postscript figures. To appear in Phys. Rev. D

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.

We present an analysis of the preliminary experimental data of direct J/{psi} production in e{sup +}e{sup {minus}} processes at low energies. We find that the color-octet contributions are crucially important to the cross section in this energy region, and their inclusion produces a good description of the data. By fitting to the data, we extract the individual values of two color-octet matrix elements: {l_angle}O{sub 8}{sup {psi}}({sup 1}S{sub 0}){r_angle}{approx}1.1{times}10{sup {minus}2} GeV{sup 3}; {l_angle}O{sub 8}{sup {psi}}({sup 3}P{sub 0}){r_angle}/m{sub c}{sup 2}{approx}7.4{times}10{sup {minus}3} GeV{sup 3}. We discuss the allowed range of the two matrix elements constrained by the theoretical uncertainties. We find that {l_angle}O{sub 8}{sup {psi}}({sup 1}S{sub 0}){r_angle} is poorly determined because it is sensitive to the variation of the choice of m{sub c}, {alpha}{sub s} and {l_angle}O{sub 1}{sup {psi}}({sup 3}S{sub 1}){r_angle}. However, {l_angle}O{sub 8}{sup {psi}}({sup 3}P{sub 0}){r_angle}/m{sub c}{sup 2} is quite stable [about (6{minus}9){times}10{sup {minus}3} GeV{sup 3}] when the parameters vary in reasonable ranges. The uncertainties due to large experimental errors are also discussed. {copyright} {ital 1997} {ital The American Physical Society}

In this paper, we discuss the prompt J/{psi} production at e{sup +}e{sup {minus}} colliders via color-singlet and color-octet production mechanisms. The color-singlet production processes include (1) e{sup +}e{sup {minus}}{r_arrow}J/{psi}gg, (2) e{sup +}e{sup {minus}}{r_arrow}J/{psi}c{bar c}, and (3) e{sup +}e{sup {minus}}{r_arrow}q{bar q}ggJ/{psi} and e{sup +}e{sup {minus}}{r_arrow}q{bar q}g{chi}{sub c} followed by {chi}{sub c}{r_arrow}J/{psi}{gamma}. The color-octet production processes include (1) e{sup +}e{sup {minus}}{r_arrow}J/{psi}g and (2) e{sup +}e{sup {minus}}{r_arrow}J/{psi}q{bar q}. Of all these production channels, we find that the color-octet contributions dominate over the color-singlet contributions at any energy scale. At low energies ({radical}(s){lt}20 GeV), the dominant channel is e{sup +}e{sup {minus}}{r_arrow}J/{psi}g whereas at high energies e{sup +}e{sup {minus}}{r_arrow}J/{psi}q{bar q} will take the leading part. We also find that the energy spectrum for the color-octet J/{psi} production in process e{sup +}e{sup {minus}}{r_arrow}J/{psi}q{bar q} is very soft, and the mean energy of the produced J/{psi} is only about 10 {endash} 20 GeV even at very high energies (e.g., at 1000 GeV). The extraction of color-octet matrix elements from J/{psi} production in e{sup +}e{sup {minus}} collisions is also discussed. {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 present a calculation of the leading order QCD fragmentation functions for gluons to split into spin-triplet $D$-wave quarkonia. We apply them to evaluate the gluon fragmentation contributions to inclusive ${}^{3}{D}_{J}$ quarkonium production at large transverse momentum processes such as the Fermilab Tevatron and find that the $D$-wave quarkonia, especially the charmonium ${2}^{\ensuremath{-}\ensuremath{-}}$ state, could be observed through the color-octet mechanism with present luminosity. Since there are distinctively large gaps between the contributions of two different (i.e., color-singlet and color-octet) quarkonium production mechanisms, our results may stand as a unique test of the NRQCD color-octet quarkonium production mechanism.

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 extend the nonrelativistic QCD (NRQCD) prediction for the production of heavy quarkonium with low transverse momentum in hadronic collisions by taking into account effects from all-order soft gluon resummation. Following the Collins-Soper-Sterman formalism, we resum the most singular terms in the partonic subprocesses. The theoretical predictions of J/ψ and Υ productions are compared to the experimental data from the fixed target experiments (E866) and the collider experiments (RHIC, Tevatron, LHC). The associated nonperturbative Sudakov form factor for the gluon distributions is found to be different from the previous assumption of rescaling the quark form factor by the ratio of color factors. This conclusion should be further checked by future experiments on Higgs boson and/or diphoton production in pp collisions. We also comment on the implication of our results on determining the color-octet matrix elements associated with the J/ψ and Υ productions in the NRQCD factorization formalism.

We present a systematic study of the proton spin structure in terms of measurable parton distributions. For a transversely-polarizedproton, we derive a polarization sum rule from the leading generalized parton distributions appearing in hard exclusive processes. For a longitudinally-polarized proton, we obtain a helicity decomposition from well-known quark and gluon helicity distributions and orbital angular-momentum contributions. The latter is shown to be related to measurable subleading generalized parton distributions and quantum-phase space Wigner distributions., 7 pages, title changed

We demonstrate the QCD factorization for inclusive hadron production in p-A collisions in the saturation formalism at one-loop order, with explicit calculation of both real and virtual gluon radiation diagrams. In particular, we find that the cross section can be written into a factorization form in the coordinate space at the next-to-leading order, while the naive form of the convolution in the transverse momentum space does not hold. The collinear divergences associated with the incoming parton distribution of the nucleon and the outgoing fragmentation function of the final-state hadron, as well as the rapidity divergence with small-x dipole gluon distribution of the nucleus are factorized into the splittings of the associated parton distribution and fragmentation functions and the energy evolution of the dipole gluon distribution function. The hard coefficient function is evaluated at one-loop order, and contains no divergence.

We show that the linearly polarized gluon distributions appear in the color dipole model as we derive the full cross sections of the DIS dijet production and the Drell-Yan dijet ($\gamma^*$ jet correlation) process. Together with the normal Weizs\"acker-Williams gluon distribution, the linearly polarized one will contribute to the DIS dijet production cross section as the coefficient of the $\cos(2 \Delta \phi) $ term in the correlation limit. We also derive the exact results for the cross section of the Drell-Yan dijet process, and find that the linearly polarized dipole gluon distribution which is identical to the normal dipole gluon distribution involves in the cross section. The results obtained in this paper agree with the previous transverse momentum dependent factorization study. We further derive the small-$x$ evolution of these linearly polarized gluon distributions and find that they rise as $x$ gets small at high energy., Comment: 10 pages,v2 with minor revision

Two widely proposed kt-dependent gluon distributions in the small-x saturation regime are investigated using two particle back-to-back correlations in high energy scattering processes. The Weizsacker-Williams gluon distribution, interpreted as the number density of gluon inside the nucleus, is studied in the quark-antiquark jet correlation in deep inelastic scattering. On the other hand, the unintegrated gluon distribution, defined as the Fourier transform of the color-dipole cross section, is probed in the direct photon-jet correlation in pA collisions. Dijet-correlation in pA collisions depends on both gluon distributions through combination and convolution in the large Nc limit., Comment: 8 pages, 1 figure

Results for the naive-time-reversal-odd quark distributions in a light-cone quark model are presented. The final-state interaction effects are generated via single-gluon exchange mechanism. The formalism of light-cone wave functions is used to derive general expressions in terms of overlap of wave-function amplitudes describing the different orbital angular momentum components of the nucleon. In particular, the model predictions show a dominant contribution from S- and P-wave interference in the Sivers function and a significant contribution also from the interference of P and D waves in the Boer-Mulders function. The favourable comparison with existing phenomenological parametrizations motivates further applications to describe azimuthal asymmetries in hadronic reactions., Comment: references and explanations added; version to appear in Phys. Rev. D

We study the spin-dependent quark distributions at large transverse momentum. We derive their transverse momentum behaviors in the collinear factorization approach in this region. We further calculate the angular distribution of the Drell-Yan lepton pair production with polarized beams and present the results in terms of the collinear twist-three quark-gluon correlation functions. In the intermediate transverse momentum region, we find that the two pproaches: the collinear factorization and the transverse momentum dependent factorization approaches are consistent in the description of the lepton pair angular distributions., Comment: 25 pages, 2 figures

We study the dihadron azimuthal correlation produced nearly back-to-back in unpolarized hadron collisions, arising from the product of two Collins fragmentation functions. Using the latest Collins fragmentation functions extracted from the global analysis of available experimental data, we make predictions for the azimuthal correlation of two-pion production in $pp$ collisions at RHIC energies. We find that the correlation is sizable in the mid-rapidity region for moderate jet transverse momentum., 13 pages, 3 figures

The leading twist transverse momentum dependent parton distribution function ${h}_{1T}^{\ensuremath{\perp}}$ is studied. We review the theoretical properties of this function, and compute it in the bag model. We find in the bag model an interesting relation, and observe it to hold also in other relativistic models: The difference between helicity and transversity distributions, often said to be a 'measure of relativistic effects' in the nucleon, is related to ${h}_{1T}^{\ensuremath{\perp}}$. This function is chirally odd and can be accessed in combination with the Collins effect in semi-inclusive deep-inelastic scattering, where it gives rise to an azimuthal single spin asymmetry proportional to $\mathrm{sin} (3\ensuremath{\phi}\ensuremath{-}{\ensuremath{\phi}}_{S})$. We discuss preliminary COMPASS data on that observable and make predictions for future experiments on various targets at JLab, COMPASS, and HERMES.

We study the azimuthal asymmetric distribution of hadrons inside a high energy jet in the single-transverse polarized nucleon-nucleon scattering, coming from the Collins effect multiplied by the quark transversity distribution. We argue that the Collins function in this process is the same as that in the semi-inclusive deep inelastic scattering. The experimental study of this process will provide us with important information on the quark transversity distribution and test the universality of the fragmentation functions.

We study the single transverse-spin asymmetry for dijet production in hadronic collisions in both the collinear QCD factorization approach and the Brodsky-Hwang-Schmidt model. We show that a nonvanishing asymmetry is generated by both initial-state and final-state interactions, and that the final-state interactions dominate. We find that in the leading kinematic region where the transverse momentum imbalance of the two jets, q_\perp = P_{1\perp}+P_{2\perp}, is much less than the momentum of either jet, the contribution from the lowest non-trivial perturbative order to both the spin-averaged and the spin-dependent dijet cross sections can be factorized into a hard part that is a function only of the averaged jet momentum P_\perp = (P_{1\perp}-P_{2\perp})/2, and perturbatively generated transverse momentum dependent (TMD) parton distributions. We show that the spin asymmetry at this non-trivial perturbative order can be described by the TMD parton distributions defined in either semi-inclusive DIS or the Drell-Yan process. We derive the same hard parts from both the collinear factorization approach and in the context of the Brodsky-Hwang-Schmidt model, verifying that they are not sensitive to details of the factorized long distance physics., 60 pages, 22 figures

${\mathrm{Cs}}_{2}\mathrm{Ag}{\mathrm{F}}_{4}$ forms a layered perovskite structure and contains $4{d}^{9}$ metal ions, similar to the $3{d}^{9}$ Cu cuprates. However, the cuprates are antiferromagnetic, while ${\mathrm{Cs}}_{2}\mathrm{Ag}{\mathrm{F}}_{4}$ is ferromagnetic. Here we investigate the electronic and magnetic properties of ${\mathrm{Cs}}_{2}\mathrm{Ag}{\mathrm{F}}_{4}$ using density functional theory (DFT) to clarify the origin of its ferromagnetism. The ground state is found to be ferromagnetic and nearly semimetallic. Because of Jahn-Teller distortions in the ${[\mathrm{Ag}{\mathrm{F}}_{6}]}^{4\ensuremath{-}}$ octahedron, the ground state has a staggered order of ${z}^{2}\text{\ensuremath{-}}{x}^{2}$ and ${z}^{2}\text{\ensuremath{-}}{y}^{2}$ orbitals. The superexchange interaction through the $\mathrm{Ag}({z}^{2}\text{\ensuremath{-}}{x}^{2})\text{--}\mathrm{F}\text{--}\mathrm{Ag}({z}^{2}\text{\ensuremath{-}}{y}^{2})$ bridge stabilizes the ferromagnetism. In order to take into account the on-site Coulomb interaction, we also perform $\mathrm{DFT}+\mathrm{U}$ calculations. The insulating state becomes the ground state, while the ferromagnetism and orbital order of ${z}^{2}\text{\ensuremath{-}}{x}^{2}$ and ${z}^{2}\text{\ensuremath{-}}{y}^{2}$ are still preserved.

Using lepton-pair production in hadron-hadron collisions as an example, we explore the relation between two well-known mechanisms for single-transverse-spin asymmetries in hard processes: twist-three quark-gluon correlations when the pair's transverse momentum is large, ${q}_{\ensuremath{\perp}}\ensuremath{\gg}{\ensuremath{\Lambda}}_{\mathrm{QCD}}$, and time-reversal-odd and transverse-momentum-dependent parton distributions when ${q}_{\ensuremath{\perp}}$ is much less than the pair's mass. We find that, although the two mechanisms each have their own domain of validity, they describe the same physics in the kinematic region where they overlap. This unifies the two mechanisms and imposes an important constraint on phenomenological studies.

We study the single-transverse spin asymmetry for the Drell-Yan process. We consider production of the lepton pair at large transverse momentum, $q_\perp\sim Q$, where $Q$ is the pair's mass. The spin asymmetry is then of higher twist and may be generated by twist-three quark-gluon correlation functions. Expanding the result for $q_\perp\ll Q$, we make contact with the transverse-momentum-dependent QCD factorization involving the so-called Sivers functions. We find that the two mechanisms, quark-gluon correlations on one hand and the Sivers effect on the other, contain the same physics in this region. This ties the two together and imposes an important constraint on phenomenological studies of single transverse spin asymmetries., Comment: 29 pages, 10 figures

We study single-spin asymmetries in semi-inclusive deep inelastic scattering with transversely polarized target. Based on the QCD factorization approach, we consider Sivers and Collins contributions to the asymmetries. We fit simple parametrizations for the Sivers and Collins functions to the recent HERMES data, and compare to results from COMPASS. Using the fitted parametrizations for the Sivers functions, we predict the single-transverse-spin asymmetries for various processes in $pp$ collisions at the Relativistic Heavy Ion Collider, including the Drell-Yan process and angular correlations in dijet and jet-plus-photon production. These asymmetries are found to be sizable at forward rapidities.

The $d$-wave superconductivity (dSC) and antiferromagnetism are analytically studied in a renormalized mean-field theory for a two-dimensional $t\text{\penalty1000-\hskip0pt}J$ model plus an on-site repulsive Hubbard interaction $U$. The purpose of introducing the $U$ term is to partially impose the no-double-occupancy constraint by employing the Gutzwiller approximation. The phase diagrams as functions of doping $\ensuremath{\delta}$ and $U$ are studied. Using the standard value of $t∕J=3.0$ and in the large-$U$ limit, we show that the antiferromagnetic (AF) order emerges and coexists with the dSC in the underdoped region below the doping $\ensuremath{\delta}\ensuremath{\sim}0.1$. The dSC order parameter increases from zero as the doping increases and reaches a maximum near the optimal doping $\ensuremath{\delta}\ensuremath{\sim}0.15$. In the small-$U$ limit, only the dSC order survives while the AF order disappears. As $U$ increases up to a critical value, the AF order shows up and coexists with the dSC in the underdoped regime. At half-filling, the system is in the dSC state for small $U$ and becomes an AF insulator for large $U$. Within the present mean-field approach, we show that the ground-state energy of the coexistent state is always lower than that of the pure dSC state.

We demonstrate a factorization formula for semi-inclusive deep-inelastic scattering with hadrons in the current fragmentation region detected at low transverse momentum. To facilitate the factorization, we introduce the transverse-momentum dependent parton distributions and fragmentation functions with gauge links slightly off the light-cone, and with soft-gluon radiations subtracted. We verify the factorization to one-loop order in perturbative quantum chromodynamics and argue that it is valid to all orders in perturbation theory., 28 pages, figures included

The electronic structures of the molecule ${\mathrm{C}}_{50}{\mathrm{Cl}}_{10}$ are studied in the framework of density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE) functional. The static polarizability $\ensuremath{\alpha}$ and second-order hyperpolarizability $\ensuremath{\gamma}$ are calculated by the use of a finite field approach. Both the average static polarizability $(⟨\ensuremath{\alpha}⟩=92.9\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{3})$ and the second hyperpolarizability $(⟨\ensuremath{\gamma}⟩=83.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}36}\phantom{\rule{0.3em}{0ex}}\mathrm{esu})$ are larger than those of ${\mathrm{C}}_{60}$. At the same time, the diagonal components of $\ensuremath{\alpha}$, especially the $\ensuremath{\gamma}$ in the $xy$ plane, which contains the Cl atoms, are much larger than those in the $z$ direction. The reason is mainly from the distribution of $\ensuremath{\pi}$ electrons of the HOMO in the planes perpendicular to the $z$ axis. We predict that ${\mathrm{C}}_{50}{\mathrm{Cl}}_{10}$ and its derivatives should be promising nonlinear optical materials.

The hadron-energy evolution (Collins and Soper) equation for all the leading-twist transverse-momentum and spin dependent parton distributions is derived in the impact parameter space. Based on the result, we present resummation formulas for the spin structure functions in the semi-inclusive deep inelastic scattering., Comment: 16 pages, 4 figures included, revised version

Generalized parton distributions at large x are studied in the perturbative QCD approach. As $\stackrel{\ensuremath{\rightarrow}}{x}1$ and at finite t, there is no t dependence for the GPDs which means that the active quark is at the center of the transverse space. We also obtain the power behavior ${H}_{q}^{\ensuremath{\pi}}(x,\ensuremath{\xi},t)\ensuremath{\sim}(1\ensuremath{-}{x)}^{2}/(1\ensuremath{-}{\ensuremath{\xi}}^{2})$ for the pion, ${H}_{q}(x,\ensuremath{\xi},t)\ensuremath{\sim}(1\ensuremath{-}{x)}^{3}/(1\ensuremath{-}{\ensuremath{\xi}}^{2}{)}^{2}$ and ${E}_{q}(x,\ensuremath{\xi},t)\ensuremath{\sim}(1\ensuremath{-}{x)}^{5}/(1\ensuremath{-}{\ensuremath{\xi}}^{2}{)}^{3}f(\ensuremath{\xi})$ for the nucleon, where $f(\ensuremath{\xi})$ represents the additional dependence on $\ensuremath{\xi}.$

In the large momentum transfer limit, generalized parton distributions can be calculated through a QCD factorization theorem which involves perturbatively-calculable hard kernels and light-cone parton distribution amplitudes of hadrons. We illustrate this through the $H_q(x,\xi,t)$ distribution for the pion and proton, presenting the hard kernels at leading order. As a result, experimental data on the generalized parton distributions in this regime can be used to determine the functional form of the parton distribution amplitudes which has thus far been quite challenging to obtain. Our result can also be used as a constraint in phenomenological GPD parametrizations., Comment: 7 pages, 4 figures; new references and figure added, errors corrected

We perform a perturbative QCD analysis of the nucleon's Pauli form factor ${F}_{2}({Q}^{2})$ in the asymptotically large ${Q}^{2}$ limit. We find that the leading contribution to ${F}_{2}({Q}^{2})$ has a $1/{Q}^{6}$ power behavior, consistent with the well-known result in the literature. Its coefficient depends on the leading- and subleading-twist light-cone wave functions of the nucleon, the latter describing the quarks with one unit of orbital angular momentum. We also derive at the logarithmic accuracy the asymptotic scaling ${F}_{2}({Q}^{2})/{F}_{1}({Q}^{2})\ensuremath{\sim}({log }^{2}{Q}^{2}/{\ensuremath{\Lambda}}^{2})/{Q}^{2}$ which describes recent Jefferson Lab data well.

Within the t-J model, we study the charge transport in underdoped bilayer cuprates by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in the electronic structure, the qualitative behavior of the charge transport is the same as in the case of single layer cuprates. The conductivity spectrum shows a low-energy peak and the unusual midinfrared band. This midinfrared band is suppressed severely with increasing temperatures, while the resistivity in the heavily underdoped regime is characterized by a crossover from the high temperature metallic-like to the low temperature insulating-like behaviors, which are consistent with the experiments., 5 pages, Revtex, three figures are included

We discuss deep inelastic scattering at high energies as a critical phenomenon in 2+1 space - time dimensions. In the limit of Bjorken $x \to 0$, $QCD$ SU(3) with quark fields becomes a critical theory with a diverging correlation length $\xi(x) \propto x^{-\frac{1}{2 \lambda_2}}$ where the exponent $\lambda_2=2.52$ is obtained from the center group Z(3) of SU(3). We conjecture that the dipole wave function of the virtual photon for transverse sizes $1/Q

The recently discovered coexistence of incommensurate antiferromagnetic neutron scattering peaks and commensurate resonance in underdoped YBa$_2$Cu$_3$O$_{6+x}$ is calling for an explanation. Within the t-J model, the doping and energy dependence of the spin dynamics of the underdoped bilayer cuprates in the normal state is studied based on the fermion-spin theory by considering the bilayer interactions. Incommensurate peaks are found at $[(1\pm\delta)\pi,\pi] $ and $[\pi,(1\pm\delta)\pi]$ at low energies with $\delta$ initially increasing with doping at low dopings and then saturating at higher dopings. These incommensurate peaks are suppressed, and the parameter $\delta$ is reduced with increasing energy. Eventually it converges to the $[\pi,\pi]$ resonance peak. Thus the recently observed coexistence is interpreted in terms of bilayer interactions., Comment: 15 pages, Revtex, five figures are included, accepted for publication in Phys. Rev. B

Fe, Cu atoms and CO molecules were manipulated with a scanning tunneling microscope (STM) on a Ag(110) surface, and one or two CO can transfer from the surface and bond with a metal atom through the STM tip [H. J. Lee and W. Ho, Science 286, 1719 (1999); Phys. Rev. B 61, R16347 (2000)]. We perform a density-functional cluster model investigation for the systems. The experimental geometries are validated and understood using the frontier orbital theory. The STM topographic images are reproduced. The vibrational frequencies of the adsorbate systems are obtained by diagonalizing the second-derivative matrices and are in excellent agreement with the experimental measurements. The geometries and C-O stretch frequencies are predicted for systems with the adsorbate metal atom being Co, Ni, Zn, and Ag. These systems can be divided to two classes, and each class exhibits a different set of properties.

The doping, temperature and energy dependence of the dynamical spin structure factors of the underdoped lanthanum cuprates in the normal state is studied within the t-J model using the fermion-spin transformation technique. Incommensurate peaks are found at $[(1\pm\delta)\pi,\pi]$, $[\pi,(1\pm\delta)\pi]$ at relatively low temperatures with $\delta$ linearly increasing with doping at the beginning and then saturating at higher dopings. These peaks broaden and weaken in amplitude with temperature and energy, in good agreement with experiments. The theory also predicts a rotation of these peaks by $\pi/4$ at even higher temperatures, being shifted to $[(1\pm \delta/\sqrt{2})\pi,(1\pm \delta/\sqrt{2})\pi]$., Comment: 11 pages, PDF file, six figures are included, accepted for publication in Physical Review B