Nuclear Theory·nucl-th

Friday·December 23, 2016

13 papers—6 primary·7 cross-listed

07
[Submitted on 21 Dec 2016] (cross-list from hep-lat)
Deconfinement, gradient and cooling scales for pure SU(2) lattice gauge theory
Bernd A. Berg🇺🇸 · David A. Clarke🇺🇸
We investigate the approach of pure SU(2) lattice gauge theory with the Wilson action to its continuum limit using the deconfining phase transition, the gradient flow and the cooling flow to set the scale. For the gradient and cooling scales we explore three different energy observables and two distinct reference values for the flow time. When the aim is to follow scaling towards the continuum limit, one gains at least a factor of 100 in computational efficiency by relying on the gradient instead of the deconfinement scale. Using cooling instead of the gradient flow one gains another factor of at least 34 in computational efficiency on the gradient flow part without any significant loss in the accuracy of scale setting. Concerning our observables, the message is to keep it simple. The Wilson action itself performs as well as or even better than the other two observables explored. Two distinct fitting forms for scaling are compared of which one connects to asymptotic scaling. Differences of the obtained estimates show that systematic errors of length ratios, though only about 1%, can be considerably larger than statistical errors of the same observables.
Comments:
13 pages, 5 figures
Subjects:
High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1612.07347 [pdf]
PRD(2017)·15 citations
08
[Submitted on 21 Dec 2016] (cross-list from gr-qc)
Lorentz-symmetry test at Planck-scale suppression with nucleons in a spin-polarized $^{133}$ Cs cold atom clock
H. Pihan-Le Bars🇫🇷 · C. Guerlin🇫🇷 · R.-D. Lasseri🇫🇷 · J.-P. Ebran🇫🇷 · Q. G. Bailey🇺🇸 · S. Bize🇫🇷 · E. Khan🇫🇷 · P. Wolf🇫🇷
We introduce an improved model that links the frequency shift of the $^{133} Cs$ hyperfine Zeeman transitions $∣ F = 3, m_{F} >⟷ ∣ F = 4, m_{F} >$ to the Lorentz-violating Standard-Model Extension (SME) coefficients of the proton and neutron. The new model uses Lorentz transformations developed to second order in boost and additionally takes the nuclear structure into account, beyond the simple Schmidt model used previously in SME analyses, thereby providing access to both proton and neutron SME coefficients including the isotropic coefficient $c ~_{T T}$ . Using this new model in a second analysis of the data delivered by the FO2 dual Cs/Rb fountain at Paris Observatory and previously analysed in arXiv:hep-ph/0601024v1, we improve by up to 12 orders of magnitude the present maximum sensitivities (see arXiv:0801.0287v9) on the $c ~_{Q}$ , $c ~_{T J}$ and $c ~_{T T}$ coefficients for the neutron and on the $c ~_{T T}$ coefficient for the proton, reaching respectively $1 0^{- 20}$ , $1 0^{- 17}$ , $1 0^{- 13}$ and $1 0^{- 15}$ GeV.
Subjects:
General Relativity and Quantum Cosmology (gr-qc); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
arXiv:
1612.07390 [pdf]
PRD(2017)·43 citations
09
[Submitted on 22 Dec 2016] (cross-list from hep-lat)
Light-quark contributions to the magnetic form factor of the Lambda(1405)
Jonathan M. M. Hall🇦🇺 · Waseem Kamleh🇦🇺 · Derek B. Leinweber🇦🇺 · Benjamin J. Menadue🇦🇺 · Benjamin J. Owen🇦🇺 · Anthony W. Thomas🇦🇺
In a recent study of the Lambda(1405), the suppression of the strange-quark contribution to the magnetic form factor was interpreted as the discovery of a dominant antikaon-nucleon composition for this low-lying state. We confirm this result by calculating the light u- and d-quark contributions to the Lambda(1405) magnetic form factor in lattice QCD in order to determine the extent to which their contributions support this exotic molecular description. Drawing on the recent graded-symmetry approach for the flavor-singlet components of the Lambda(1405), the separation of connected and disconnected contributions is performed in both the flavor-octet and singlet representations. The relationship between light-quark contributions to the Lambda(1405) magnetic form factor and the connected contributions of the nucleon magnetic form factors is established and compared with lattice calculations of the same quantities, confirming the KN molecular structure of the Lambda(1405) in lattice QCD.
Subjects:
High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1612.07477 [pdf]
PRD(2017)·34 citations
10
[Submitted on 22 Dec 2016] (cross-list from hep-ph)
Magnetic-Field Induced Critical Endpoint
Stefan Rechenberger🇩🇪
The phase diagram of strong interaction matter is analyzed utilizing the Nambu--Jona-Lasinio model. Special emphasis is placed on its dependence on an external magnetic field and isospin chemical potential. Using flavor mixing induced by instanton effects the influence of isospin breaking due to the magnetic field and the isospin chemical potential is compared. It is found that at low temperatures and large quark chemical potential the magnetic field, depending on its strength, induces a new critical endpoint or a triple point.
Comments:
8 pages, 5 figures, references added in second version
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1612.07541 [pdf]
PRD(2017)·9 citations
11
[Submitted on 22 Dec 2016] (cross-list from hep-lat)
Strong isospin violation and chiral logarithms in the baryon spectrum
David A. Brantley🇺🇸 · Balint Joo🇺🇸 · Ekaterina V. Mastropas🇺🇸 · Emanuele Mereghetti🇺🇸 · Henry Monge-Camacho🇺🇸 · Brian C. Tiburzi🇺🇸 · Andre Walker-Loud🇺🇸
We present a precise lattice QCD calculation of the contribution to the neutron-proton mass splitting arising from strong isospin breaking, $m_{n} - m_{p} ∣_{QC D} = 2.32 \pm 0.17$ MeV. We also determine $m_{Ξ^{-}} - m_{Ξ^{0}} ∣_{QC D} = 5.44 \pm 0.31$ MeV. The calculation is performed at three values of the pion mass, with several values of the quark mass splitting and multiple lattice volumes, but only a single lattice spacing and an estimate of discretization errors. The calculations are performed on the anisotropic clover-Wilson ensembles generated by the Hadron Spectrum Collaboration. The omega-baryon mass is used to set the scale $a_{t}^{- 1} = 6111 \pm 127$ MeV, while the kaon masses are used to determine the value of the light-quark mass spitting. The nucleon mass splitting is then determined as a function of the pion mass. We observe, for the first time, conclusive evidence for non-analytic light quark mass dependence in lattice QCD calculations of the baryon spectrum. When left as a free parameter, the fits prefer a nucleon axial coupling of $g_{A} = 1.24 (56)$ . To highlight the presence of this chiral logarithm in the nucleon mass splitting, we also compute the isospin splitting in the cascade-baryon system which is less sensitive to chiral dynamics. Finally, we update the best lattice QCD determination of the CP-odd pion-nucleon coupling that would arise from a non-zero QCD theta-term, $g ˉ_{0} / (2 f_{π}) = (14.7 \pm 1.8 \pm 1.4) \cdot 1 0^{- 3} θ ˉ$ . The original lattice QCD correlation functions, analysis results and extrapolated quantities are packaged in HDF5 files made publicly available including a simple Python script to access the numerical results, construct effective mass plots along with our analysis results, and perform the extrapolations of various quantities determined in this work.
Comments:
16 pages including figures and tables. The original lattice QCD correlation functions and our analysis results can be found at this address http://ntc0.lbl.gov/~walkloud/mn_mns_mp/ stored in HDF5 format. Additionally, there are a number of Python files which can be used to access the original results and our analysis, see the README.txt to get started
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1612.07733 [pdf]
45 citations
12
[Submitted on 22 Dec 2016] (cross-list from hep-ph)
Helicity Evolution at Small x: Summary of Recent Developments
Yuri V. Kovchegov🇺🇸 · Daniel Pitonyak🇺🇸 · Matthew D. Sievert🇺🇸
We construct small- $x$ evolution equations which can be used to calculate quark and anti-quark helicity TMDs and PDFs, along with the $g_{1}$ structure function. These evolution equations resum powers of $α_{s} ln^{2} (1/ x)$ in the polarization-dependent evolution along with the powers of $α_{s} ln (1/ x)$ in the unpolarized evolution which includes saturation effects. The equations are written in an operator form in terms of polarization-dependent Wilson line-like operators. While the equations do not close in general, they become closed and self-contained systems of non-linear equations in the large- $N_{c}$ and large- $N_{c} & N_{f}$ limits. We construct a numerical solution of the helicity evolution equations in the large- $N_{c}$ limit. Employing the extracted intercept, we are able to predict directly from theory the behavior of the quark helicity PDFs at small $x$ , which should have important phenomenological consequences. We also give an estimate of how much of the proton's spin may be at small $x$ and what impact this has on the so-called "spin crisis." Based on JHEP 1601 (2016) 072 (arXiv:1511.06737), arXiv:1610.06197 and arXiv:1610.06188.
Comments:
8 pages, 6 figures; combined proceedings of "QCD Evolution 2016" workshop, Amsterdam, Netherlands, May 30 - June 3, 2016 and the 22nd International Spin Symposium (SPIN 2016), Champaign, IL, USA, September 26 - 30, 2016. Based on JHEP 1601 (2016) 072 (arXiv:1511.06737), arXiv:1610.06197 and arXiv:1610.06188
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1612.07758 [pdf]
0 citations
13
[Submitted on 22 Dec 2016] (cross-list from hep-ph)
Exploring correlations in the CGC wave function: odd azimuthal anisotropy
Alex Kovner🇺🇸 · Michael Lublinsky🇮🇱 · Vladimir Skokov🇺🇸
We extend the CGC approach to calculation of the double inclusive gluon production by including high-density effect in the CGC wave function of the projectile (proton). Our main result is that these effects lead to the appearance of odd harmonics in the two-particle correlation C(k,p). We find that in the high momentum limit, |k|,|p|>>Q_s, this results in a positive c_1{2}. Additionally when the magnitudes of the two momenta are approximately equal, |k|/|p| ~ 1, the density effects also generate a positive third harmonic c_3{2}, which translates into a non-vanishing v_3 when the momenta of the trigger and associated particle are in the same momentum bin. The sign of c_3{2} becomes negative when |k|/|p|>1.1 suggesting an interesting experimental signature.
Comments:
32 pages; 5 figures; version accepted to Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1612.07790 [pdf]
PRD(2017)·44 citations

Affiliations

first authorsco-authorsvia INSPIRE

Deconfinement, gradient and cooling scales for pure SU(2) lattice gauge theory

Lorentz-symmetry test at Planck-scale suppression with nucleons in a spin-polarized 133Cs cold atom clock

Light-quark contributions to the magnetic form factor of the Lambda(1405)

Magnetic-Field Induced Critical Endpoint

Strong isospin violation and chiral logarithms in the baryon spectrum

Helicity Evolution at Small x: Summary of Recent Developments

Exploring correlations in the CGC wave function: odd azimuthal anisotropy

Affiliations

Lorentz-symmetry test at Planck-scale suppression with nucleons in a spin-polarized $^{133}$ Cs cold atom clock