Nuclear Theory·nucl-th

Tuesday·November 22, 2016

21 papers—7 primary·14 cross-listed

08
Nucleon resonance structure in the finite volume of lattice QCD
Jia-Jun Wu🇦🇺 · H. Kamano🇯🇵 · T.-S. H. Lee🇺🇸 · D. B. Leinweber🇦🇺 · A.W. Thomas🇦🇺
An approach for relating the nucleon resonances extracted from $π N$ reaction data to lattice QCD calculations has been developed by using the finite-volume Hamiltonian method. Within models of $π N$ reactions, bare states are introduced to parametrize the intrinsic excitations of the nucleon. We show that the resonance pole positions can be related to the probability $P_{N^{*}} (E)$ of finding the bare state, $N^{*}$ , in the $π N$ scattering states in infinite volume. We further demonstrate that the probability $P_{N^{*}}^{V} (E)$ of finding the same bare states in the eigenfunctions of the underlying Hamiltonian in finite volume approaches $P_{N^{*}} (E)$ as the volume increases. Our findings suggest that the comparison of $P_{N^{*}} (E)$ and $P_{N^{*}}^{V} (E)$ can be used to examine whether the nucleon resonances extracted from the $π N$ reaction data within the dynamical models are consistent with lattice QCD calculation. We also discuss the measurement of $P_{N^{*}}^{V} (E)$ directly from lattice QCD. The practical differences between our approach and the approach using the Lüscher formalism to relate LQCD calculations to the nucleon resonance poles embedded in the data are also discussed.
↳ hep-lathep-phnucl-exnucl-thPRD(2017)·22 citations
09
Merging symmetry projection methods with coupled cluster theory: Lessons from the Lipkin model Hamiltonian
Jacob M Wahlen-Strothman · Thomas M. Henderson · Matthew R. Hermes · Matthias Degroote · Yiheng Qiu · Jinmo Zhao · Jorge Dukelsky · Gustavo E. Scuseria
Coupled cluster and symmetry projected Hartree-Fock are two central paradigms in electronic structure theory. However, they are very different. Single reference coupled cluster is highly successful for treating weakly correlated systems, but fails under strong correlation unless one sacrifices good quantum numbers and works with broken-symmetry wave functions, which is unphysical for finite systems. Symmetry projection is effective for the treatment of strong correlation at the mean-field level through multireference non-orthogonal configuration interaction wavefunctions, but unlike coupled cluster, it is neither size extensive nor ideal for treating dynamic correlation. We here examine different scenarios for merging these two dissimilar theories. We carry out this exercise over the integrable Lipkin model Hamiltonian, which despite its simplicity, encompasses non-trivial physics for degenerate systems and can be solved via diagonalization for a very large number of particles. We show how symmetry projection and coupled cluster doubles individually fail over different correlation limits, whereas models that merge these two theories are highly successful over the entire phase diagram. Despite the simplicity of the Lipkin Hamiltonian, the lessons learned in this work will be useful for building an ab initio symmetry projected coupled cluster theory that we expect to be accurate over the weakly and strongly correlated limits, as well as the recoupling regime.
↳ cond-mat.str-elnucl-thJ.Chem.Phys.(2017)·17 citations
10
Inverse Magnetic Catalysis from improved Holographic QCD in the Veneziano limit
Umut Gürsoy🇳🇱 · Ioannis Iatrakis🇳🇱 · Matti Järvinen🇫🇷 · Govert Nijs🇳🇱
We study the dependence of the chiral condensate on external magnetic field in the context of holographic QCD at large number of flavors. We consider a holographic QCD model where the flavor degrees of freedom fully backreact on the color dynamics. Perturbative QCD calculations have shown that $B$ acts constructively on the chiral condensate, a phenomenon called "magnetic catalysis". In contrast, recent lattice calculations show that, depending on the number of flavors and temperature, the magnetic field may also act destructively, which is called "inverse magnetic catalysis". Here we show that the holographic theory is capable of both behaviors depending on the choice of parameters. For reasonable choice of the potentials entering the model we find qualitative agreement with the lattice expectations. Our results provide insight for the physical reasons behind the inverse magnetic catalysis. In particular, we argue that the backreaction of the flavors to the background geometry decatalyzes the condensate.
↳ hep-thhep-phnucl-thJHEP(2017)·65 citations
11
String point of view for heavy-light mesons
Yubing Dong🇨🇳 · Qi-Fang Lü🇨🇳 · Takayuki Matsuki🇯🇵
An approximate rotational symmetry of a heavy-light meson is viewed from a string picture. Using a simple string configuration, we derive a formula, $(M - m_{c})^{2} = π σ L$ , whose coefficient of the r.h.s. is just 1/2 of that of a light meson with two light quarks. A numerical plot is obtained for $D$ mesons of experimental data as well as several theoretical models, which shows good agreement with this formula.
↳ hep-phhep-exnucl-thEPJ Web Conf.(2017)·0 citations
12
A gauge invariant Debye mass for the complex heavy-quark potential
Yannis Burnier🇨🇭 · Alexander Rothkopf🇩🇪
The concept of a screening mass is a powerful tool to simplify the intricate physics of in-medium test charges surrounded by light charge carriers. While it has been successfully used to describe electromagnetic properties, its definition and computation in QCD is plagued by questions of gauge invariance and the presence of non-perturbative contributions from the magnetic sector. Here we present a recent alternative definition of a gauge invariant Debye mass parameter following closely the original idea of Debye and Hueckel. Our test charges are a static heavy quark-antiquark pair whose complex potential and its in-medium modification can be extracted using lattice QCD. By combining in a generalized Gauss-Law the non-perturbative aspects of quark binding with a perturbative ansatz for the medium effects, we succeed to describe the lattice values of the potential with a single temperature dependent parameter, in turn identified with a Debye mass. We find that its behavior, as evaluated in a recent quenched lattice QCD study, deviates from that in other approaches, such as hard-thermal-loop perturbation theory or from electric field correlators on the lattice. In particular around the phase transition its values tend to zero significantly faster than at weak-coupling.
↳ hep-lathep-phnucl-thPoS(2016)·1 citation
13
What lattice QCD spectral functions can tell us about heavy quarkonium in the QGP
Alexander Rothkopf🇩🇪
The bound states of a heavy quark and antiquark ( $c c ˉ, b b ˉ$ ) are ideal probes to explore the quark-gluon plasma created in relativistic heavy-ion collisions at the RHIC and LHC. Not only have they become experimentally accessible with high precision but also efficient tools, so called effective field theories (EFT) have been developed to treat them theoretically. Here we present recent progress in understanding the in-medium behavior of heavy-quarkonium with the help of EFT's combined with non-perturbative and first principles simulations in lattice QCD. In particular we discuss computations of heavy quarkonium spectral functions with the help of Bayesian unfolding methods and the physics we can extract from them. Limitations and the underlying assumptions of the used approaches are pointed out.
↳ hep-lathep-phnucl-thPoS(2016)·3 citations
14
Quarkonia at $T > 0$ and lattice QCD
Alexander Rothkopf🇩🇪
We report here on recent progress in the determination of S-wave and P-wave heavy-quarkonium states at finite temperature. Our results are based on the combination of effective field theories with numerical lattice QCD simulations. These non-perturbative tools allow us to compute the heavy-quarkonium in-medium spectral functions, from which we in turn determine the melting temperatures of individual states and estimate phenomenologically relevant observables, such as the $ψ^{'}$ to J/ $ψ$ ratio in heavy-ion collisions.
↳ hep-phhep-latnucl-thEPJ Web Conf.(2017)·2 citations
15
Novel picture of the soft modes at the QCD critical point based on the FRG method
Takeru Yokota🇯🇵 · Teiji Kunihiro🇯🇵 · Kenji Morita🇯🇵
We investigate the soft mode at the QCD critical point (CP) on the basis of the functional renormalization group. We calculate the spectral functions in the meson channels in the two-flavor quark--meson model. Our result shows that the energy of the peak position of the particle--hole mode in the sigma channel becomes vanishingly small as the system approaches the QCD CP, which is a manifestation of the softening of the phonon mode. We also extract the dispersion curves of the mesonic and the phonon mode, a hydrodynamic mode which leads to a finding that the dispersion curve of the sigma-mesonic mode crosses the light-cone into the space-like momentum region, and then eventually merges into the phonon mode as the system approaches further close to the CP. This may suggest that the sigma-mesonic mode forms the soft mode together with the hydrodynamic mode at the CP.
↳ hep-phnucl-thActa Phys.Polon.Supp.(2017)·1 citation
16
Exotic-Hadron Signature by Constituent-Counting Rule in Perturbative QCD
Wen-Chen Chang🇹🇼 · H. Kawamura🇯🇵 · S. Kumano🇯🇵 · T. Sekihara🇯🇵
We explain a method to find internal quark configurations of exotic hadron candidates by using the constituent counting rule. The counting rule was theoretically predicted in perturbative QCD for hard exclusive hadron reactions, and it has been tested in experiments for stable hadrons including compound systems of hadrons such as the deuteron, $^{3}$ H, and $^{3}$ He. It indicates that the cross section scales as $d σ / d t \sim 1/ s^{n - 2}$ , where $s$ is the center-of-mass energy squared and $n$ is the total number of constituents. We apply this method for finding internal configurations of exotic hadron candidates, especially $Λ (1405)$ . There is a possibility that $Λ (1405)$ could be five-quark state or a $K ˉ N$ molecule, and scaling properties should be different between the ordinary three-quark state or five-quark one. We predict such a difference in $π^{-} + p \to K^{0} + Λ (1405)$ , and it could be experimentally tested, for example, at J-PARC. On the other hand, there are already measurements for $γ + p \to K^{+} + Λ (1405)$ as well as the ground $Λ$ in photoproduction reactions. Analyzing such data, we found an interesting indication that $Λ (1405)$ looks like a five-quark state at medium energies and a three-quark one at high energies. However, accurate higher-energy measurements are necessary for drawing a solid conclusion, and it should be done at JLab by using the updated 12 GeV electron beam. Furthermore, we discuss studies of exotic hadron candidates, such as $f_{0} (980)$ and $a_{0} (980)$ , in electron-positron annihilation by using generalized distribution amplitudes and the counting rule. These studies should be possible as a KEKB experiment.
↳ hep-phhep-exhep-latnucl-ex+1JPS Conf.Proc.(2017)·1 citation
17
Spectral functions in functional renormalization group approach -- analysis of the collective soft modes at the QCD critical point --
Takeru Yokota🇯🇵 · Teiji Kunihiro🇯🇵 · Kenji Morita🇯🇵
We first review the method to calculate the spectral functions in the functional renormalization group (FRG) approach, which has been recently developed. We also provide the numerical stability conditions given by the present authors for a generic nonlinear evolution equation that are necessary for obtaining the accurate effective potential from the flow equation in the FRG. As an interesting example, we report the recent calculation of the spectral functions of the mesonic and particle-hole excitations using a chiral effective model of Quantum Chromodynamics (QCD); we extract the dispersion relations from them and try to reveal the nature of the soft modes at the QCD critical point (CP) where the phase transition is second order. Our result shows that a clear development and the softening of the phonon mode in the space-like region as the system approaches the CP; furthermore it turns out that the sigma mesonic mode once in the time-like region gets to merge with the phonon mode in the close vicinity of the CP, implying a novel possibility about the nature of the soft mode of the QCD CP.
↳ hep-phnucl-th3 citations
18
QCD phase diagram with isospin chemical potential
Bastian B. Brandt🇩🇪 · Gergely Endrodi🇩🇪
In this contribution we investigate the phase diagram of QCD in the presence of an isospin chemical potential. To alleviate the infrared problems of the theory associated with pion condensation, we introduce the pionic source as an infrared regulator. We discuss various methods to extrapolate the results to vanishing pionic source, including a novel method based on the singular value spectrum of the massive Dirac operator, a leading-order reweighting and a spline Monte-Carlo fit. Our main results concern the phase transition boundary between the normal and the pion condensation phases and the chiral/deconfinement transition temperature as a function of the chemical potential. In addition, we perform a quantitative comparison between our direct results and a Taylor-expansion obtained at zero chemical potential to assess the applicability range of the latter.
↳ hep-lathep-phnucl-thPoS(2016)·66 citations
19
In-medium rho-meson properties in a light-front approach
J. P. B. C. de Melo🇧🇷 · K. Tsushima (Laboratorio de Fısica Teórica e Computacional - LFTC, Universidade Cruzeiro do Sul)🇧🇷
Properties of h̊o}-meson in symmetric nuclear matter are investigated within a light-front constituent quark model (LFCQM), using the in-medium input calculated by the quark-meson coupling (QMC) model. The LFCQM used here was previously applied in vacuum to calculate the h̊o}-meson electromagnetic properties, namely, charge G 0 , magnetic G 1 , and quadrupole G 2 form factors, as well as the electromagnetic radius and decay constant. We predict the in-medium modifications of the h̊o}-meson electromagnetic form factors in symmetric nuclear matter.
↳ hep-phhep-thnucl-thFew Body Syst.(2017)·5 citations
20
Electromagnetic Effects on Strongly Interacting QCD-Matter
Abdel Magied Abdel Aal Diab🇪🇬 · Abdel Nasser Tawfik (Egyptian Ctr. Theor. Phys., Cairo, WLCAPP, Cairo)🇪🇬 · M. T. Hussein (Cairo U.)🇪🇬
In order to study the temperature dependence of the quark-hadron phase structure and the QCD equation of state in vanishing and finite magnetic field, the SU(3) Polyakov linear-sigma model is utilized. In mean field approximation, the dependence of various magnetic properties such as magnetization, magnetic susceptibility and magnetic catalysis is analyzed in finite magnetic field. Furthermore, the influences of finite magnetic field on the temperature dependence of some transport properties (viscosity and conductivity) from Green-Kubo correlation are characterized.
↳ hep-lathep-phnucl-th2 citations
21
Towards the understanding of jet substructures and cross sections in heavy ion collisions using soft collinear effective theory
Yang-Ting Chien🇺🇸
The jet quenching phenomenon in heavy ion collisions provides a strong evidence of the modification of parton shower in the quark-gluon plasma (QGP). Jet substructure observables can probe various aspects of the jet formation mechanism. They contain useful information about the QGP and allow us to study the medium properties in great details. Here we present theoretical calculations of jet shapes and cross sections in proton-proton and lead-lead collisions at the LHC using soft-collinear effective theory, with Glauber gluon interactions in the medium. We find that resumming large logarithms in the jet substructure calculation is necessary for precise theoretical predictions. The resummation is performed using renormalization group evolution between characteristic jet scales. We also find that the medium induces power corrections to jet shapes. In the end we present the comparison between our calculations with the recent measurements at the LHC with very good agreement. Our calculations help initiate precise jet modification studies in heavy ion collisions.
↳ hep-phnucl-thPoS(2016)·1 citation

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first authorsco-authorsvia INSPIRE