Nuclear Theory·nucl-th

Thursday·June 1, 2017

11 papers—5 primary·6 cross-listed

06
Optimized perturbation theory applied to the study of the thermodynamics and BEC-BCS crossover in the three-color Nambu--Jona-Lasinio model
Dyana C. Duarte🇧🇷 · R. L. S. Farias🇧🇷 · Patrícia H. A. Manso🇧🇷 · Rudnei O. Ramos🇧🇷
The Nambu--Jona-Lasinio model with two flavors, three colors and diquark interactions is analyzed in the context of optimized perturbation theory (OPT). Corrections to the thermodynamical potential that go beyond the large- $N_{c}$ (LN) approximation are taken into account, and the region of the phase diagram corresponding to intermediate chemical potentials and very low temperatures is explored. The simultaneous presence of both the quark-antiquark and diquark condensates can cause the system to behave as a fluid composed of a Bose-Einstein condensate (BEC) or a color superconductor one, in the form of a Bardeen-Cooper-Schrieffer (BCS) superfluid. The BEC-BCS crossover is then studied in the nonperturbative OPT scheme. The results obtained in the context of the OPT method are then contrasted with those obtained in the LN approximation. We show that there are values for the coupling constants related to quark-quark and quark-antiquark interactions where the corrections beyond LN brought by the OPT method can influence the behavior of the diquark condensate and the effective quark mass as a function of the baryon chemical potential. These changes in the behavior of the phase structure of the model modify the location of the critical point related to the phase structure as a whole of the model. Also, when we impose the color neutrality condition, our results show that the nature of the phase transition can change as well, shifting the ratio of the quark-antiquark and quark-quark interactions to higher values in the OPT case as compared to the LN approximation.
↳ hep-phhep-thnucl-thPRD(2017)·10 citations
07
Hard exclusive neutrino production of a light meson
B. Pire🇫🇷 · L. Szymanowski🇵🇱 · J. Wagner🇵🇱
We update the leading order in $α_{s}$ QCD amplitude for deep exclusive neutrino and antineutrino production of a light meson on an unpolarized nucleon. The factorization theorems of the collinear QCD approach allow us to write the amplitude as the convolution of generalized parton distributions (GPDs) and perturbatively calculable coefficient functions. We study both the pseudoscalar meson and longitudinally polarized vector meson cases. It turns out that, contrarily to the electroproduction case, the leading twist scattering amplitudes for $π$ and $ρ_{L}$ productions are proportional to one another, which may serve as an interesting new test of the leading twist dominance of exclusive processes at medium scale. The dominance of the gluonic contribution to most cross sections is stressed.
↳ hep-phhep-exnucl-exnucl-thPRD(2017)·16 citations
08
Lorentz Structure of Vector Part of Matrix Elements of Transitions n <-> p, Caused by Strong Low-Energy Interactions and Hypothesis of Conservation of Charged Vector Current
A. N. Ivanov🇦🇹
We analyse the Lorentz structure of the matrix elements of the transitions "neutron <-->proton", induced by the charged hadronic vector current. We show that the term maintaining conservation of the charged hadronic vector current even for different masses of the neutron and proton (see T. Leitner et al., Phys. Rev. C 73, 065502 (2006) and A. M. Ankowski, arXiv:1601.06169 [hep-ph]) has a dynamical origin, related to the G-even first class current contribution. We show that because of invariance of strong low-energy interactions under the G-parity transformations, the G-odd contribution with the Lorentz structure $q_{μ}$ , where $q_{μ}$ is a momentum transferred, does not appear in the matrix elements of the ``neutron <-> proton' transitions.
↳ hep-phhep-exnucl-exnucl-thJ.Phys.G(2018)·9 citations
09
Precise Test of Internal-Conversion Theory: alpha_K Measurements for Transitions in Nine Nuclei Spanning Z values from 45 to 78
J.C. Hardy · N. Nica · V.E. Iacob · M.B. Trzhaskovskaya
We have been testing the theory used to calculate internal-conversion coefficients (ICCs) by making a series of measurements of alpha_K values with precision better than +/-2%. So far we have measured E3 transitions in three nuclei, 103Rh, 111Cd and 134Cs; and M4 transitions in six nuclei, 119Sn, 125Te, 127Te, 137Ba, 193Ir and 197Pt. Together, these span a wide range of A and Z values. In all cases, the results strongly favor Dirac-Fock calculations in which the final-state electron wave function has been computed in an atomic field that includes the vacancy created by the internal-conversion process.
↳ nucl-exnucl-thAppl.Radiat.Isot.(2018)·2 citations
10
Universality in fermionic dimer-dimer scattering
A. Deltuva
Collisions of two fermionic dimers near the unitary limit are studied using exact four-particle equations for transition operators in momentum space. Universal properties of dimer-dimer phase shifts and effective range expansion (ERE) parameters are determined. The inclusion of the fourth-order momentum term in the ERE significantly extends its validity to higher collision energies. The dimer-dimer scattering length and effective range are determined in the unitary limit as well as their corrections arising due to the finite range of the two-fermion interaction. These results are of considerably higher accuracy as compared to previous works, but confirm most of the previous results except for the lattice effective field theory calculations.
↳ cond-mat.quant-gasnucl-thphysics.atom-phPRA(2017)·6 citations
11
Low-energy modes of spin-imbalanced Fermi gases in BCS phase
F. Matera · M. F. Wagner
The low-energy modes of a spin-imbalanced superfluid Fermi gas in the Bardeen-Cooper-Schrieffer (BCS) side are studied. The gas is assumed to be sufficiently dilute so that the pairing of atoms can be considered effective only in s-wave between fermions of different internal state. The order parameter at equilibrium is determined by the mean-field approximation, while the properties of the collective modes are calculated within a Gaussian approximation for the fluctuations of the order parameter. In particular we investigate the effects of asymmetry between the populations of the two different components and of temperature on the frequency and damping of collective modes. It is found that the temperature does not much affect the frequency and the damping of the modes, whereas an increase of the imbalance shifts the frequency toward lower values and enhances the damping sensitively. Besides the Bogoliubov-Anderson phonons, we observe modes at zero frequency for finite values of the wave-number. These modes indicate that an instability develops driving the system toward two separate phases, normal and superfluid.
↳ cond-mat.quant-gasnucl-thEur.Phys.J.D(2017)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Optimized perturbation theory applied to the study of the thermodynamics and BEC-BCS crossover in the three-color Nambu--Jona-Lasinio model

Hard exclusive neutrino production of a light meson

Lorentz Structure of Vector Part of Matrix Elements of Transitions n <-> p, Caused by Strong Low-Energy Interactions and Hypothesis of Conservation of Charged Vector Current

Precise Test of Internal-Conversion Theory: alpha_K Measurements for Transitions in Nine Nuclei Spanning Z values from 45 to 78

Universality in fermionic dimer-dimer scattering

Low-energy modes of spin-imbalanced Fermi gases in BCS phase

Affiliations