55544629
Universality of TMD correlators
In a high-energy scattering process with hadrons in the initial state, color is involved. Transverse momentum dependent distribution functions (TMDs) describe the quark and gluon distributions in these hadrons in momentum space with the inclusion of transverse directions. Apart from the (anti)-quarks and gluons that are involved in the hard scattering process, additional gluon emissions by the hadrons have to be taken into account as well, giving rise to Wilson lines or gauge links. The TMDs involved are sensitive to the process under consideration and hence potentially nonuniversal due to these Wilson line interactions with the hard process; different hard processes give rise to different Wilson line structures. We will show that in practice only a finite number of universal TMDs have to be considered, which come in different linear combinations depending on the hard process under consideration, ensuring a generalized universality. For quarks this gives rise to three Pretzelocity functions, whereas for gluons a richer structure of functions arises.
17694907
Transverse Spin in QCD. II. Sum Rule and Radiative Corrections
In this paper we address various issues connected with transverse spin in light front QCD. The transverse spin operators, in A+ = 0 gauge, expressed in terms of the dynamical variables are explicitly interaction dependent unlike the helicity operator which is interaction independent in the topologically trivial sector of light-front QCD. In analogy with the helicity sum rule, we propose a sum rule for transverse spin. We perform a one loop renormalization of the full transverse spin operator in light-front Hamiltonian perturbation theory for a dressed quark state. We explicitly show that all the terms dependent on the center of mass momenta get canceled in the matrix element. The entire non-vanishing contribution comes from the fermion intrinsic-like part of the transverse spin operator. We verify the sum rule for a dressed quark state upto O(αs) in perturbation theory. We compare and contrast the calculations of transverse spin and helicity of a dressed quark in perturbation theory. PACS Numbers: 11.10.Ef, 11.30.Cp, 12.38.Bx, 13.88.+e
15898613
Diffraction patterns in deeply virtual compton scattering
We report on a calculation to show that the Fourier transform of the Deeply Virtual Compton Scattering (DVCS) amplitude with respect to the skewness variable ζ at fixed invariant momentum transfer squared t gives results that are analogous to the diffractive scattering of a wave in optics. As a specific example, we utilize the quantum fluctuations of a fermion state at one loop in QED to obtain the behavior of the DVCS amplitude for electron‐photon scattering. We then simulate the wavefunctions for a hadron by differentiating the above LFWFs with respect to M2 and study the corresponding DVCS amplitudes in light‐front longitudinal space.
2554754
ON THE SIZE OF HADRONS
The form factor and the mean-square radius of the pion are calculated analytically from a parametrized form of a wave function. The numerical wave function was obtained previously by solving numerically an eigenvalue equation for the pion in a particular model. The analytical formulas are of more general interest than just being valid for the pion and can be generalized to the case with unequal quark masses. Two different parametrizations are investigated. Because of the highly relativistic problem, noticeable deviations from a nonrelativistic formula are obtained.
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.
119229539
Photon Generalized Parton Distributions
We present a calculation of the generalized parton distributions of the photon using overlaps of photon light-front wave functions.
6841250
Quantum Monte Carlo calculations of neutron matter with nonlocal chiral interactions.
We present fully nonperturbative quantum Monte Carlo calculations with nonlocal chiral effective field theory (EFT) interactions for the ground-state properties of neutron matter. The equation of state, the nucleon chemical potentials, and the momentum distribution in pure neutron matter up to one and a half times the nuclear saturation density are computed with a newly optimized chiral EFT interaction at next-to-next-to-leading order. This work opens the way to systematic order by order benchmarking of chiral EFT interactions and ab initio prediction of nuclear properties while respecting the symmetries of quantum chromodynamics.
118408897
Metropolis Monte Carlo integration on the Lefschetz thimble: Application to a one-plaquette model
We propose a new algorithm based on the Metropolis sampling method to perform Monte Carlo integration for path integrals in the recently proposed formulation of quantum field theories on the Lefschetz thimble. The algorithm is based on a mapping between the curved manifold defined by the Lefschetz thimble of the full action and the flat manifold associated with the corresponding quadratic action. We discuss an explicit method to calculate the residual phase due to the curvature of the Lefschetz thimble. Finally, we apply this new algorithm to a simple one-plaquette model where our results are in perfect agreement with the analytic integration. We also show that for this system the residual phase does not represent a sign problem.
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.
67814332
An efficient method to compute the residual phase on a Lefschetz thimble
We propose an efficient method to compute the so-called residual phase that appears when performing Monte Carlo calculations on a Lefschetz thimble. The method is stochastic and its cost scales linearly with the physical volume, linearly with the number of stochastic estimators and quadratically with the length of the extra dimension along the gradient flow. This is a drastic improvement over previous estimates of the cost of computing the residual phase. We also report on basic tests of correctness and scaling of the code.
118482889
Quantum Monte Carlo with Coupled-Cluster wave functions
ECT*, Villa Tambosi, I-38123 Villazzano (Trento), Italy(Dated: May 3, 2013)We introduce a novel many body method which combines two powerful many body techniques,viz., quantum Monte Carlo and coupled cluster theory. Coupled cluster wave functions are intro-duced as importance functions in a Monte Carlo method designed for the conﬁguration interactionframework to provide rigorous upper bounds to the ground state energy. We benchmark our methodon the homogeneous electron gas in momentum space. The importance function used is the coupledcluster doubles wave function. We show that the computational resources required in our methodscale polynomially with system size. Our energy upper bounds are in very good agreement withprevious calculations of similar accuracy, and they can be systematically improved by includinghigher order excitations in the coupled cluster wave function.