22141493
Odd-particle systems in the shell model Monte Carlo method: circumventing a sign problem.
The shell model Monte Carlo method is a powerful technique to calculate thermal and ground-state properties of strongly correlated finite-size systems. However, its application to odd-particle-number systems has been hampered by the sign problem that originates from the projection on an odd number of particles. We circumvent this sign problem for the ground-state energy by extracting the ground-state energy of the odd-particle-number system from the asymptotic behavior of the imaginary-time single-particle Green's function of the even-particle-number system. We apply this method to calculate pairing gaps of nuclei in the iron region. Our results are in good agreement with experimental pairing gaps.
124451495
Lefschetz thimble Monte Carlo for many-body theories: A Hubbard model study
119254846
Variational theory of hot nucleon matter. II. Spin-isospin correlations and equation of state of nuclear and neutron matter
We apply the variational theory for fermions at finite temperature and high density, developed in an earlier paper, to symmetric nuclear matter and pure neutron matter. This extension generalizes to finite temperatures, the many body technique used in the construction of the zero temperature Akmal-Pandharipande-Ravenhall equation of state. We discuss how the formalism can be used for practical calculations of hot dense matter. Neutral pion condensation along with the associated isovector spin longitudinal sum rule is analyzed. The equation of state is calculated for temperatures less than 30 MeV and densities less than three times the saturation density of nuclear matter. The behavior of the nucleon effective mass in medium is also discussed.
117551201
Quantum field theories on the Lefschetz thimble
In these proceedings, we summarize the Lefschetz thimble approach to the sign problem of Quantum Field Theories. In particular, we review its motivations, and we summarize the results of the application of two different algorithms to two test models.
100464553
Level densities of nickel isotopes: microscopic theory versus experiment
We apply a spin-projection method to calculate microscopically the level densities of a family of nickel isotopes $^{59-64}$Ni using the shell model Monte Carlo approach in the complete $pfg_{9/2}$ shell. Accurate ground-state energies of the odd-mass nickel isotopes, required for the determination of excitation energies, are determined using the Green's function method recently introduced to circumvent the odd particle-number sign problem. Our results are in excellent agreement with recent measurements based on proton evaporation spectra and with level counting data at low excitation energies. We also compare our results with neutron resonance data, assuming equilibration of parity and a spin-cutoff model for the spin distribution at the neutron binding energy, and find good agreement with the exception of $^{63}$Ni.
119532334
Variational theory of hot nucleon matter
We develop a variational theory of hot nuclear matter in neutron stars and supernovae. It can also be used to study charged, hot nuclear matter which may be produced in heavy-ion collisions. This theory is a generalization of the variational theory of cold nuclear and neutron star matter based on realistic models of nuclear forces and pair correlation operators. The present approach uses microcanonical ensembles and the variational principle obeyed by the free energy. In this paper we show that the correlated states of the microcanonical ensemble at a given temperature T and density {rho} can be orthonormalized preserving their diagonal matrix elements of the Hamiltonian. This allows for the minimization of the free energy without corrections from the nonorthogonality of the correlated basis states, similar to that of the ground state energy. Samples of the microcanonical ensemble can be used to study the response, and the neutrino luminosities and opacities of hot matter. We present methods to orthonormalize the correlated states that contribute to the response of hot matter.
119238580
Asymmetries involving dihadron fragmentation functions: from DIS to e+e- annihilation
Using a model calculation of dihadron fragmentation functions, we fit the spin asymmetry recently extracted by HERMES for the semi-inclusive pion pair production in deep-inelastic scattering on a transversely polarized proton target. By evolving the obtained dihadron fragmentation functions, we make predictions for the correlation of the angular distributions of two pion pairs produced in electron-positron annihilations at BELLE kinematics. Our study shows that the combination of two-hadron inclusive deep-inelastic scattering and electron-positron annihilation measurements can provide a valid alternative to Collins effect for the extraction of the quark transversity distribution in the nucleon.
15766151
Twist Four Longitudinal Structure Function for a Positronium-like Bound State in Weak Coupling Light-Front QED
To have an analytic understanding of the higher-twist structure functions, we calculate twist four longitudinal structure function for a positronium-like bound state in weak coupling light-front QED. We verify a previously proposed sum rule for twist four FL in the weak coupling theory. We find that in the weakly coupled system, the fermionic part of FL, which is actually measured in DIS experiments, is related to the kinetic energy of the fermions and not to the interaction. The sum rule in this case reduces to a relation connecting the kinetic and the potential energies to the binding energy of positronium in the non-relativistic limit. Using the analytic form of the wave function of positronium in this limit, we find that FL is sharply peaked at x = 12 at fixed value of Q 2.
118677327
Twist three distribution e(x): Sum rules and equation of motion relations
Abstract We investigate the twist three distribution function e ( x ) in light-front Hamiltonian perturbation theory. In light-front gauge, by eliminating the constrained field, we find a mass term, an intrinsic transverse momentum dependent term and a ‘genuine twist three’ quark–gluon interaction term in the operator. The equation of motion relation, moment relation and the sum rules are satisfied for a quark at one loop. We compare the results with other model calculations.
118539581
On transverse spin sum rules
Abstract In this work we show that (i) both the form factors A i and C ¯ i contribute to the matrix element of the energy–momentum tensor T i + − in a transversely polarized state, (ii) there is no relative suppression factor between these two contributions and (iii) the contribution to the matrix element of the Pauli–Lubanski operator W i ⊥ from that of T i + + contains only the form factor B i and not the form factor A i . These results support our criticism and the conclusions as stated in Ref. [13] . Comparing and contrasting the spin sum rules in two different approaches, one advocated by us and the one proposed by Jaffe and Manohar, we point out that the physical content of the sum rules is very transparent in our approach, whereas, in the second approach details of the dynamics remain hidden and the separation into orbital and intrinsic spin parts is not visible.
119183210
Comment on Phys. Rev. Lett. 109, 152005 (2012)
The identifications of transverse boost and rotation operators in light front theory done in Phys. Rev. Lett. {109}, 152005 (2012) is incorrect. The simple parton interpretation claimed is, in fact, for the transverse boost operator. Manifestation of Lorentz symmetry as claimed in the context of their calculation involving transverse Pauli-Lubanski polarization vector is unsupported.