- Light-Front Interpretation of Proton Generalized Polarizabilities
Author(s): M. Gorchtein, C. Lorcé, B. Pasquini, and M. Vanderhaeghen
We extend the recently developed formalism to extract light-front quark charge densities from nucleon form factor data to the deformations of these quark charge densities when applying an external electric field. We show that the resulting induced polarizations can be extracted from proton generalized polarizabilities. The available data for the generalized electric polarizability of the proton yield a pronounced structure in its induced polarization at large transverse distances, which will be pinned down by forthcoming high precision virtual Compton scattering experiments.
[Phys. Rev. Lett. 104, 112001] Published Mon Mar 15, 2010
- Backward dilepton production in color dipole and parton models
Author(s): Maria Beatriz Gay Ducati and Emmanuel Gräve de Oliveira
The Drell–Yan dilepton production at backward rapidities is studied in proton-nucleus collisions at Relativistic Heavy Ion Collider and LHC energies by comparing two different approaches: the k_{T} factorization at next-to-leading order with intrinsic transverse momentum and the same process formulated in the target rest frame, i.e., the color dipole approach. Our results are expressed in terms of the ratio between p(d)-A and p-p collisions as a function of transverse momentum and rapidity. Three nuclear parton distribution functions are used: EKS (Eskola, Kolhinen, and Ruuskanen), EPS08, and EPS09 and, in both approaches, dileptons show sensitivity to nuclear effects, specially regarding the intrinsic transverse momentum. Also, there is room to discriminate between formalisms: the color dipole approach lacks soft effects introduced by the intrinsic k_{T} . Geometric scaling GBW (Golec-Biernat and Wusthoff) and BUW (Boer, Utermann, and Wessels) color dipole cross section models and also a DHJ (Dumitru, Hayashigaki, and Jalilian-Marian) model, which breaks geometric scaling, are used. No change in the ratio between collisions is observed, showing that this observable is not changed by the particular shape of the color dipole cross section. Furthermore, our k_{T} factorization results are compared with color glass condensate results at forward rapidities: the results agree at Relativistic Heavy Ion Collider although disagree at LHC, mainly due to the different behavior of target gluon and quark shadowing.
[Phys. Rev. D 81, 054015] Published Mon Mar 15, 2010
- Equation of state for physical quark masses
Author(s): M. Cheng, S. Ejiri, P. Hegde, F. Karsch, O. Kaczmarek, E. Laermann, R. D. Mawhinney, C. Miao, S. Mukherjee, P. Petreczky, C. Schmidt, and W. Soeldner
We calculate the QCD equation of state for temperatures corresponding to the transition region with physical mass values for two degenerate light quark flavors and a strange quark using an improved staggered fermion action (p4-action) on lattices with temporal extent N_{τ} =8. We compare our results with previous calculations performed at twice larger values of the light quark masses as well as with results obtained from a resonance gas model calculation. We also discuss the deconfining and chiral aspects of the QCD transition in terms of renormalized Polyakov loop, strangeness fluctuations, and subtracted chiral condensate. We show that compared to the calculations performed at twice larger value of the light quark mass the transition region shifts by about 5 MeV toward smaller temperatures.
[Phys. Rev. D 81, 054504] Published Mon Mar 15, 2010
- Eccentricity Fluctuations Make Flow Measurable in High Multiplicity p-p Collisions
Author(s): Jorge Casalderrey-Solana and Urs Achim Wiedemann
Elliptic flow is a hallmark of collectivity in hadronic collisions. Its measurement relies on analysis techniques which require high event multiplicity and so far can only be applied to heavy ion collisions. Here, we delineate the conditions under which elliptic flow becomes measurable in the samples of high-multiplicity (dN_{ch} /dy≥50) p-p collisions, which will soon be collected at the LHC. We observe that fluctuations in the p-p interaction region can result in a sizable spatial eccentricity even for the most central p-p collisions. Under relatively mild assumptions on the nature of such fluctuations and on the eccentricity scaling of elliptic flow, we find that the resulting elliptic flow signal in high-multiplicity p-p collisions at the LHC becomes measurable with standard techniques.
[Phys. Rev. Lett. 104, 102301] Published Fri Mar 12, 2010
- Transitions in eigenvalue and wavefunction structure in (1+2) -body random matrix ensembles with spin
Author(s): Manan Vyas, V. K. B. Kota, and N. D. Chavda
Finite interacting Fermi systems with a mean-field and a chaos generating two-body interaction are modeled by one plus two-body embedded Gaussian orthogonal ensemble of random matrices with spin degree of freedom [called EGOE(1+2)-s ]. Numerical calculations are used to demonstrate that, as λ , the strength of the interaction (measured in the units of the average spacing of the single-particle levels defining the mean-field), increases, generically there is Poisson to GOE transition in level fluctuations, Breit-Wigner to Gaussian transition in strength functions (also called local density of states) and also a duality region where information entropy will be the same in both the mean-field and interaction defined basis. Spin dependence of the transition points λ_{c} , λ_{F} , and λ_{d} , respectively, is described using the propagator for the spectral variances and the formula for the propagator is derived. We further establish that the duality region corresponds to a region of thermalization. For this purpose we compared the single-particle entropy defined by the occupancies of the single-particle orbitals with thermodynamic entropy and information entropy for various λ values and they are very close to each other at λ=λ_{d} .
[Phys. Rev. E 81, 036212] Published Fri Mar 12, 2010
- Heavy-quarkonium production in high energy proton-proton collisions at RHIC
Author(s): Stanley J. Brodsky and Jean-Philippe Lansberg
We update the study of the total ψ and Υ production cross section in proton-proton collisions at RHIC energies using the QCD-based color-singlet model, including next-to-leading order partonic matrix elements. We also include charm-quark initiated processes which appear at leading order in α_{s} , so far overlooked in such studies. Contrary to earlier claims, we show that the color-singlet yield is consistent with measurements over a broad range of J/ψ rapidities. We find that intrinsic plus sealike charm-initiated processes contribute more than 20% of the direct J/ψ yield. The key signature for such processes is the observation of a charm-quark jet opposite in azimuthal angle ϕ to the detected J/ψ. Our results have impact on the proper interpretation of heavy-quarkonium production in heavy-ion collisions and its use as a probe for the quark-gluon plasma.
[Phys. Rev. D 81, 051502] Published Thu Mar 11, 2010
- Evolution of fluctuations near QCD critical point
Author(s): M. A. Stephanov
We propose to describe the time evolution of quasistationary fluctuations near QCD critical point by a system of stochastic Boltzmann-Langevin-Vlasov-type equations. We derive the equations and study the system analytically in the linearized regime. Known results for equilibrium stationary fluctuations as well as the critical scaling of diffusion coefficient are reproduced. We apply the approach to the long-standing question of the fate of the critical point fluctuations during the hadronic rescattering stage of the heavy-ion collision after chemical freeze-out. We find that if conserved particle number fluctuations survive the rescattering, so do, under a certain additional condition, the fluctuations of nonconserved quantities, such as mean transverse momentum. We derive a simple analytical formula for the magnitude of this memory effect.
[Phys. Rev. D 81, 054012] Published Thu Mar 11, 2010
- Confirmation of Quark-Hadron Duality in the Neutron F_{2} Structure Function
Author(s): S. P. Malace, Y. Kahn, W. Melnitchouk, and C. E. Keppel
We apply a recently developed technique to extract for the first time the neutron F_{2}^{n} structure function from inclusive proton and deuteron data in the nucleon resonance region, and test the validity of quark-hadron duality in the neutron. We establish the accuracy of duality in the low-lying neutron resonance regions over a range of Q^{2} , and compare with the corresponding results on the proton and with theoretical expectations. The confirmation of duality in both the neutron and proton opens the possibility of using resonance region data to constrain parton distributions at large x.
[Phys. Rev. Lett. 104, 102001] Published Tue Mar 09, 2010
- Meson properties at finite temperature in a three flavor nonlocal chiral quark model with Polyakov loop
Author(s): G. A. Contrera, D. Gómez Dumm, and Norberto N. Scoccola
We study the finite temperature behavior of light scalar and pseudoscalar meson properties in the context of a three-flavor nonlocal chiral quark model. The model includes mixing with active strangeness degrees of freedom, and takes care of the effect of gauge interactions by coupling the quarks with the Polyakov loop. We analyze the chiral restoration and deconfinement transitions, as well as the temperature dependence of meson masses, mixing angles and decay constants. The critical temperature is found to be T_{c} ≃202 MeV, in better agreement with lattice results than the value recently obtained in the local SU(3) PNJL model. It is seen that above T_{c} pseudoscalar meson masses get increased, becoming degenerate with the masses of their chiral partners. The temperatures at which this matching occurs depend on the strange quark composition of the corresponding mesons. The topological susceptibility shows a sharp decrease after the chiral transition, signalling the vanishing of the U(1)_{A} anomaly for large temperatures.
[Phys. Rev. D 81, 054005] Published Tue Mar 09, 2010
- Predictions for high-energy pp and p [over ¯] p scattering from a finite sum of gluon ladders
Author(s): R. Fiore, L. Jenkovszky, E. Kuraev, A. Lengyel, and Z. Tarics
An eikonalized elastic proton-proton and proton-antiproton scattering amplitude F(s,t), calculated from QCD as a finite sum of gluon ladders, is compared with the existing experimental data on the total cross section and the ratio ρ(s,0)=ReF(s,0)/ImF(s,0) of the real part to the imaginary part of the forward amplitude. Predictions for the expected LHC energies are given.
[Phys. Rev. D 81, 056001] Published Tue Mar 09, 2010
- Erratum: Extraction of the Light Quark Mass Ratio from the Decays ψ^{′} →J/ψπ^{0} (η) [Phys. Rev. Lett. 103, 082003 (2009)]
Author(s): Feng-Kun Guo, Christoph Hanhart, and Ulf-G. Meißner
[Phys. Rev. Lett. 104, 109901] Published Mon Mar 08, 2010
- Effect of atomic electrons on the 7.6-eV nuclear transition in ^{229} Th^{3+}
Author(s): S. G. Porsev and V. V. Flambaum
We have considered an effect of atomic electrons on the nuclear ^{229m} Th- ^{229g} Th transition in ^{229} Th^{3+} due to the electronic bridge process. Based on a recent experimental result we assumed the energy difference between the isomeric and the ground nuclear states to be equal to 7.6 eV. We have calculated the ratios of the electronic bridge process probability (Γ_{EB} ) to the probability of the nuclear radiative transition (Γ_{N} ) for the electronic 5f_{5/2} →6d_{3/2} ,6d_{5/2} ,7s and the 7s→7p_{1/2} ,7p_{3/2} transitions and found Γ_{EB} /Γ_{N} ~0.01-0.1 for the former and Γ_{EB} /Γ_{N} ~20 for the latter.
[Phys. Rev. A 81, 032504] Published Mon Mar 08, 2010
- Electron penetration into the nucleus and its effect on the quadrupole interaction
Author(s): Katrin Koch, Klaus Koepernik, Dimitri Van Neck, Helge Rosner, and Stefaan Cottenier
A series expansion of the interaction between a nucleus and its surrounding electron distribution provides terms that are well-known in the study of hyperfine interactions: the familiar quadrupole interaction and the less familiar hexadecapole interaction. If the penetration of electrons into the nucleus is taken into account, various corrections to these multipole interactions appear. The best known correction is a scalar term related to the isotope shift and the isomer shift. This paper discusses a related tensor correction, which modifies the quadrupole interaction if electrons penetrate the nucleus: the quadrupole shift. We describe the mathematical formalism and provide first-principles calculations of the quadrupole shift for a large set of solids. Fully relativistic calculations that explicitly take a finite nucleus into account turn out to be mandatory. Our analysis shows that the quadrupole shift becomes appreciably large for heavy elements. Implications for experimental high-precision studies of quadrupole interactions and quadrupole moment ratios are discussed. A literature review of other small quadrupole-like effects is presented as well (pseudoquadrupole effect, isotopologue anomaly, etc.).
[Phys. Rev. A 81, 032507] Published Mon Mar 08, 2010
- Final-state spectrum of ^{3} He after β^{-} decay of tritium anions T^{-}
Author(s): Alexander Stark and Alejandro Saenz
The final-state spectrum of β decaying tritium anions T^{-} was calculated. The wave functions describing the initial T^{-} ground state and the final ^{3} He states were obtained by the full configuration-interaction method. The transition probability was calculated within the sudden approximation. The transition probability into the electronic continuum was extracted from the complex-scaled resolvent and shown to converge for very high energies to an approximate analytical model probability distribution.
[Phys. Rev. A 81, 032501] Published Fri Mar 05, 2010
- Fragmentation functions in nuclear media
Author(s): Rodolfo Sassot, Marco Stratmann, and Pia Zurita
We perform a detailed phenomenological analysis of how well hadronization in nuclear environments can be described in terms of effective fragmentation functions. The medium modified fragmentation functions are assumed to factorize from the partonic scattering cross sections and evolve in the hard scale in the same way as the standard or vacuum fragmentation functions. Based on precise data on semi-inclusive deep-inelastic scattering off nuclei and hadron production in deuteron-gold collisions, we extract sets of effective fragmentation functions for pions and kaons at next-to-leading order accuracy. The obtained sets provide a rather accurate description of the kinematical dependence of the analyzed cross sections and are found to differ significantly from standard fragmentation functions both in shape and magnitude. Our results support the notion of factorization and universality in the studied nuclear environments, at least in an effective way and within the precision of the available data.
[Phys. Rev. D 81, 054001] Published Thu Mar 04, 2010
- Confinement models at finite temperature and density
Author(s): Pok Man Lo and Eric S. Swanson
In-medium chiral symmetry breaking in confining potential models of QCD is examined. Past attempts to analyze these models have been hampered by infrared divergences that appear at nonzero temperature. We argue that previous attempts to circumvent this problem are not satisfactory and demonstrate a simple resolution. We also show that the expectation that confining models do not exhibit a chiral phase transition is incorrect. The effect of summing ring diagrams is investigated, and we present the first determination of the temperature-density phase diagram for three model systems. We find that observables and the phase structure of the confinement models depend strongly on whether vacuum polarization is accounted for. Finally, it appears that standard confinement models cannot adequately describe both hadron phenomenology and in-medium properties of QCD.
[Phys. Rev. D 81, 034030] Published Fri Feb 26, 2010
- Stopping distance for high energy jets in weakly coupled quark-gluon plasmas
Author(s): Peter Arnold, Sean Cantrell, and Wei Xiao
We derive a simple formula for the stopping distance for a high-energy quark traveling through a weakly coupled quark-gluon plasma. The result is given to next-to-leading order in an expansion in inverse logarithms ln(E/T), where T is the temperature of the plasma. We also define a stopping distance for gluons and give a leading-log result. Discussion of stopping distance has a theoretical advantage over discussion of energy loss rates in that stopping distances can be generalized to the case of strong coupling, where one may not speak of individual partons.
[Phys. Rev. D 81, 045017] Published Mon Feb 22, 2010
- Precise Determination of the Strong Coupling Constant at NNLO in QCD from the Three-Jet Rate in Electron–Positron Annihilation at LEP
Author(s): G. Dissertori, A. Gehrmann-DeRidder, T. Gehrmann, E. W. N. Glover, G. Heinrich, and H. Stenzel
We present the first determination of the strong coupling constant from the three-jet rate in e^{+} e^{-} annihilation at LEP, based on a next-to-next-to-leading-order (NNLO) perturbative QCD prediction. More precisely, we extract α_{s} (M_{Z} ) by fitting perturbative QCD predictions at O(α_{s}^{3} ) to data from the ALEPH experiment at LEP. Over a large range of the jet-resolution parameter y_{cut} , this observable is characterized by small nonperturbative corrections and an excellent stability under renormalization scale variation. We find α_{s} (M_{Z} )=0.1175±0.0020(expt)±0.0015(theor), which is more accurate than the values of α_{s} (M_{Z} ) from e^{+} e^{-} event-shape data currently used in the world average.
[Phys. Rev. Lett. 104, 072002] Published Fri Feb 19, 2010
- Spectral Structure of the Pygmy Dipole Resonance
Author(s): A. P. Tonchev, S. L. Hammond, J. H. Kelley, E. Kwan, H. Lenske, G. Rusev, W. Tornow, and N. Tsoneva
High-sensitivity studies of E1 and M1 transitions observed in the reaction ^{138} Ba(γ [over →] ,γ^{′} ) at energies below the one-neutron separation energy have been performed using the nearly monoenergetic and 100% linearly polarized photon beams of the HIγ [over →] S facility. The electric dipole character of the so-called “pygmy” dipole resonance was experimentally verified for excitations from 4.0 to 8.6 MeV. The fine structure of the M1 “spin-flip” mode was observed for the first time in N=82 nuclei.
[Phys. Rev. Lett. 104, 072501] Published Thu Feb 18, 2010
- Anisotropic hydrodynamics, bulk viscosities, and r-modes of strange quark stars with strong magnetic fields
Author(s): Xu-Guang Huang, Mei Huang, Dirk H. Rischke, and Armen Sedrakian
In strong magnetic fields the transport coefficients of strange quark matter become anisotropic. We determine the general form of the complete set of transport coefficients in the presence of a strong magnetic field. By using a local linear response method, we calculate explicitly the bulk viscosities ζ_{⊥} and ζ_{∥} transverse and parallel to the B field, respectively, which arise due to the nonleptonic weak processes u+s↔u+d. We find that for magnetic fields B<10^{17} G, the dependence of ζ_{⊥} and ζ_{∥} on the field is weak, and they can be approximated by the bulk viscosity for the zero magnetic field. For fields B>10^{18} G, the dependence of both ζ_{⊥} and ζ_{∥} on the field is strong, and they exhibit de Haas–van Alphen–type oscillations. With increasing magnetic field, the amplitude of these oscillations increases, which eventually leads to negative ζ_{⊥} in some regions of parameter space. We show that the change of sign of ζ_{⊥} signals a hydrodynamic instability. As an application, we discuss the effects of the new bulk viscosities on the r-mode instability in rotating strange quark stars. We find that the instability region in strange quark stars is affected when the magnetic fields exceed the value B=10^{17} G. For fields which are larger by an order of magnitude, the instability region is significantly enlarged, making magnetized strange stars more susceptible to r-mode instability than their unmagnetized counterparts.
[Phys. Rev. D 81, 045015] Published Thu Feb 18, 2010
- LHC potential for study of the small x gluon physics in ultraperipheral collisions of 3.5 TeV protons
Author(s): V. Rebyakova, M. Strikman, and M. Zhalov
We argue that already the first year LHC run at sqrt[s] =7 TeV will provide a quick and effective way to test the dynamics of the color dipole-gluon interactions and the small x behavior of the gluon density in the proton by studying vector meson photoproduction in ultraperipheral proton-proton collisions.
[Phys. Rev. D 81, 031501] Published Fri Feb 12, 2010
- Pionic contribution to neutrinoless double beta decay
Author(s): J. D. Vergados, Amand Faessler, and H. Toki
It is well known that neutrinoless double decay is going to play a crucial role in settling the neutrino properties, which cannot be extracted from the neutrino oscillation data. It is, in particular, expected to settle the absolute scale of neutrino mass and determine whether the neutrinos are Majorana particles, i.e. they coincide with their own antiparticles. In order to extract the average neutrino mass from the data, one must be able to estimate the contribution of all possible high mass intermediate particles. The latter, which occur in practically all extensions of the standard model, can, in principle, be differentiated from the usual mass term, if data from various targets are available. One, however, must first be able to reliably calculate the corresponding nuclear matrix elements. Such calculations are extremely difficult since the effective transition operators are very short ranged. For such operators processes like pionic contributions, which are usually negligible, turn out to be dominant. We study such an effect in a nonrelativistic quark model for the pion and the nucleon.
[Phys. Rev. D 81, 034018] Published Fri Feb 12, 2010
- Connecting Polyakov loops to the thermodynamics of SU(N_{c} ) gauge theories using the gauge-string duality
Author(s): Jorge Noronha
We show that in four-dimensional gauge theories dual to five-dimensional Einstein gravity coupled to a single scalar field in the bulk, the derivative of the single heavy quark free energy in the deconfined phase is dF_{Q} (T)/dT∼-1/c_{s}^{2} (T), where c_{s} (T) is the speed of sound. This general result provides a direct link between the softest point in the equation of state of strongly-coupled plasmas and the deconfinement phase transition described by the expectation value of the Polyakov loop. We give an explicit example of a gravity dual with black hole solutions that can reproduce the lattice results for the expectation value of the Polyakov loop and the thermodynamics of SU(3) Yang-Mills theory in the (nonperturbative) temperature range between T_{c} and 3T_{c} .
[Phys. Rev. D 81, 045011] Published Fri Feb 12, 2010
- High Transverse Momentum Triggered Correlations over a Large Pseudorapidity Acceptance in Au+Au Collisions at sqrt[s_{NN} ] =200 GeV
Author(s): B. Alver et al.
A measurement of two-particle correlations with a high transverse momentum trigger particle (p_{T}^{trig} >2.5 GeV/c) is presented for Au+Au collisions at sqrt[s_{NN} ] =200 GeV over the uniquely broad longitudinal acceptance of the PHOBOS detector (-4<Δη<2). A broadening of the away-side azimuthal correlation compared to elementary collisions is observed at all Δη. As in p+p collisions, the near side is characterized by a peak of correlated partners at small angle relative to the trigger particle. However, in central Au+Au collisions an additional correlation extended in Δη and known as the “ridge” is found to reach at least |Δη|≈4. The ridge yield is largely independent of Δη over the measured range, and it decreases towards more peripheral collisions. For the chosen p_{T}^{trig} cut, the ridge yield is consistent with zero for events with less than roughly 100 participating nucleons.
[Phys. Rev. Lett. 104, 062301] Published Thu Feb 11, 2010
- New parton distributions from large-x and low-Q^{2} data
Author(s): A. Accardi, M. E. Christy, C. E. Keppel, W. Melnitchouk, P. Monaghan, J. G. Morfín, and J. F. Owens
We report results of a new global next-to-leading order fit of parton distribution functions in which cuts on W and Q are relaxed, thereby including more data at high values of x. Effects of target mass corrections, higher twist contributions, and nuclear corrections for deuterium data are significant in the large-x region. The leading twist parton distributions are found to be stable to target mass correction model variations as long as higher twist contributions are also included. The behavior of the d quark as x→1 is particularly sensitive to the deuterium corrections, and using realistic nuclear smearing models the d-quark distribution at large x is found to be softer than in previous fits performed with more restrictive cuts.
[Phys. Rev. D 81, 034016] Published Thu Feb 11, 2010
- Hyperon electromagnetic properties in two-flavor chiral perturbation theory
Author(s): Fu-Jiun Jiang and Brian C. Tiburzi
The pion-mass dependence of hyperon electromagnetic properties is determined using two-flavor heavy baryon chiral perturbation theory. Specifically we compute chiral corrections to the charge radii, magnetic moments, and magnetic radii of the spin one-half hyperons, as well as the charge radii, magnetic moments, magnetic radii, electric quadrupole moments, and quadrupole radii of the spin three-half hyperons. Results for the nucleon and delta are also included. Efficacy of the two-flavor theory is investigated by analyzing the role played by virtual kaons. For the electromagnetic properties of spin one-half hyperons, kaon loop contributions are shown to be well described by terms analytic in the pion mass squared. Similarly kaon contributions to the magnetic moments of spin three-half hyperons are well described in the two-flavor theory. The remaining electromagnetic properties of spin three-half resonances can be described in two-flavor chiral perturbation theory, however, this description fails just beyond the physical pion mass. For the case of experimentally known hyperon magnetic moments and charge radii, we demonstrate that chiral corrections are under reasonable control, in contrast to the behavior of these observables in the three-flavor chiral expansion. The formulas we derive are ideal for performing the pion-mass extrapolation of lattice QCD data obtained at the physical strange quark mass.
[Phys. Rev. D 81, 034017] Published Thu Feb 11, 2010
- Nucleon electromagnetic form factors from lattice QCD using 2+1 flavor domain wall fermions on fine lattices and chiral perturbation theory
Author(s): S. N. Syritsyn, J. D. Bratt, M. F. Lin, H. B. Meyer, J. W. Negele, A. V. Pochinsky, M. Procura, M. Engelhardt, Ph. Hägler, T. R. Hemmert, and W. Schroers (LHPC Collaboration)
We present a high-statistics calculation of nucleon electromagnetic form factors in N_{f} =2+1 lattice QCD using domain wall quarks on fine lattices, to attain a new level of precision in systematic and statistical errors. Our calculations use 32^{3} ×64 lattices with lattice spacing a=0.084 fm for pion masses of 297, 355, and 403 MeV, and we perform an overdetermined analysis using on the order of 3600 to 7000 measurements to calculate nucleon electric and magnetic form factors up to Q^{2} ≈1.05 GeV^{2} . Results are shown to be consistent with those obtained using valence domain wall quarks with improved staggered sea quarks, and using coarse domain wall lattices. We determine the isovector Dirac radius r_{1}^{v} , Pauli radius r_{2}^{v} and anomalous magnetic moment κ_{v} . We also determine connected contributions to the corresponding isoscalar observables. We extrapolate these observables to the physical pion mass using two different formulations of two-flavor chiral effective field theory at one loop: the heavy baryon small scale expansion and covariant baryon chiral perturbation theory. The isovector results and the connected contributions to the isoscalar results are compared with experiment, and the need for calculations at smaller pion masses is discussed.
[Phys. Rev. D 81, 034507] Published Thu Feb 11, 2010
- Baryons in QCD_{AS} at large N_{c} : A roundabout approach
Author(s): Thomas D. Cohen, Daniel L. Shafer, and Richard F. Lebed
QCD_{AS} , a variant of large N_{c} QCD in which quarks transform under the color two-index antisymmetric representation, reduces to standard QCD at N_{c} =3 and provides an alternative to the usual large N_{c} extrapolation that uses fundamental representation quarks. Previous strong plausibility arguments assert that the QCD_{AS} baryon mass scales as N_{c}^{2} ; however, the complicated combinatoric problem associated with quarks carrying two color indices impeded a complete demonstration. We develop a diagrammatic technique to solve this problem. The key ingredient is the introduction of an effective multigluon vertex: a “traffic circle” or roundabout diagram. We show that arbitrarily complicated diagrams can be reduced to simple ones with the same leading N_{c} scaling using this device, and that the leading contribution to baryon mass does, in fact, scale as N_{c}^{2} .
[Phys. Rev. D 81, 036006] Published Thu Feb 11, 2010
- Dissociation of a heavy meson in the quark medium
Author(s): Chanyong Park
We investigate the dissociation of a heavy meson in the medium composed of light quarks and gluons. In the quark-gluon plasma, the dissociation length of the heavy meson becomes short as the temperature or quark chemical potential increases. On the contrary, in the hadronic phase the dissociation length becomes large as the chemical potential increases, due to the different dissociation mechanism with one used in the quark-gluon plasma.
[Phys. Rev. D 81, 045009] Published Tue Feb 09, 2010
- Thermodynamics of a field theory with an infrared fixed point from gauge/gravity duality
Author(s): J. Alanen and K. Kajantie
We use gauge/gravity duality to study the thermodynamics of a field theory with asymptotic freedom in the ultraviolet and a fixed point in the infrared. We find a high temperature quark-gluon phase and a low T conformal unparticle phase. The phase transition between the phases is of first order or continuous, depending on the ratio of the radii of asymptotic anti–de Sitter spaces at T=0 and T=∞. This is a prediction from a model of gauge/gravity duality, not yet verified on the field theory side.
[Phys. Rev. D 81, 046003] Published Tue Feb 09, 2010
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