Nuclear Theory·nucl-th

Tuesday·November 19, 2019

14 papers—8 primary·6 cross-listed

01
Lepton-Proton Two-Photon Exchange in Chiral Perturbation Theory
Pulak Talukdar🇮🇳 · Vanamali C. Shastry🇮🇳 · Udit Raha🇮🇳 · Fred Myhrer🇺🇸
We use heavy baryon chiral perturbation theory to evaluate the two-photon exchange corrections to the low-energy elastic lepton-proton scattering at next-to-leading order accuracy, i.e., $O (α, M^{- 1})$ , including a non-zero lepton mass. We consider the elastic proton intermediate state in the two-photon exchange together in the soft photon approximation. The infrared singular contributions are projected out using dimensional regularization. The resulting infrared singularity-free two-photon exchange contribution is in good numerical agreement with existing predictions based on standard diagrammatic soft photon approximation evaluations.
nucl-thhep-phPRD(2020)·22 citations
02
Isospin Dependence in Fission Fragment Yields
S. Garg · B. Maheshwari · D. Choudhury · A. K. Jain
In the present paper, we explore the idea of isospin conservation in new situations and contexts based on the directions provided by our earlier works. We present the results of our calculations for the relative yields of neutron-rich fission fragments emitted in fast neutron-induced fission, 238U (n, fission) reaction by using the concept of the conservation of isospin and compare with the experimental data. Our results successfully reproduced the gross features of partition wise fission fragments distribution of 238U (n, fission). This confirms that in all kinds of fission, isospin remains pure in neutron-rich systems even at high excitations. Thus, isospin can be proven as an important quantum number for the prediction of fission fragment distribution.
nucl-thDAE Symp.Nucl.Phys.(2019)·0 citations
03
$Ξ^{-} t$ quasibound state instead of $ΛΛ nn$ bound state
H. Garcilazo🇲🇽 · A. Valcarce🇪🇸 · J. Vijande🇪🇸
We study the coupled $ΛΛ nn - Ξ^{-} p nn$ system to check whether the inclusion of channel coupling is able to bind the $ΛΛ nn$ system. We use a separable potential three-body model of the coupled $ΛΛ nn - Ξ^{-} p nn$ system as well as a variational four-body calculation with realistic interactions. Our results exclude the possibility of a $ΛΛ nn$ bound state by a large margin. However, we have found a $Ξ^{-} t$ quasibound state above the $ΛΛ nn$ threshold.
nucl-thhep-phCPC(2020)·4 citations
04
The d*(2380) and its family of pion assisted dibaryons
Avraham Gal🇮🇱
The status of $N Δ$ and $ΔΔ$ dibaryons introduced by Dyson and Xuong in 1964 is briefly reviewed with focus on the d*(2380), tentatively assigned as a $ΔΔ$ dibaryon resonance. It is argued that the apparently small value of width, $Γ_{d^{*}}$ $\approx$ 70 MeV, favors hadronic structure for the d*(2380) dibaryon rather than a six-quark structure.
nucl-thhep-phnucl-ex0 citations
05
Analysis of the Multi-component Relativistic Boltzmann Equation for Electron Scattering in Big Bang Nucleosynthesis
Nishanth Sasankan · Atul Kedia · Motohiko Kusakabe · Grant J Mathews
Big-bang nucleosynthesis (BBN) is valuable as a means to constrain the physics of the early universe and it is the only probe of the radiation-dominated epoch. A fundamental assumption in BBN is that the nuclear velocity distributions obey Maxwell-Boltzmann (MB) statistics as they do in stars. Specifically, the BBN epoch is characterized by a dilute baryon plasma for which the velocity distribution of nuclei is mainly determined by the dominant Coulomb elastic scattering with mildly relativistic electrons. One must therefore deduce the momentum distribution for reacting nuclei from the multi-component relativistic Boltzmann equation. However, the full multi-component relativistic Boltzmann equation has only recently been analyzed and its solution has only been worked out in special cases. Moreover, a variety of schemes have been proposed that introduce non-thermal components into the BBN environment which can alter the thermal distribution of reacting nuclei. Here, we construct the relativistic Boltzmann equation in the context of BBN. We also derive a Langevin model and perform relativistic Monte-Carlo simulations which clarify the baryon distribution during BBN and can be used to analyze any relaxation from a non-thermal injection. We show by these analyses that the thermalization process leads to a nuclear distribution function that remains very close to MB statistics even during the most relativistic environment relevant to BBN. Hence, the predictions of standard BBN remain unchanged.
nucl-thastro-ph.COPRD(2020)·11 citations
06
Vector-boson condensates, spin-triplet superfluidity of paired neutral and charged fermions, and $3 P_{2}$ pairing of nucleons
D. N. Voskresensky🇷🇺
After reminding of properties of the condensate of the complex scalar field in the external uniform magnetic field $H$ focus is made on the study of phases of the complex neutral vector boson fields coupled with magnetic field by the Zeeman coupling and phases of the charged vector boson fields. These systems may behave as nonmagnetic and ferromagnetic superfluids and ordinary and ferromagnetic superconductors. Response of the ferromagnetic superfluid and superconducting systems occupying half of space on the external uniform static magnetic field $H$ is thoroughly studied. Then the spin-triplet pairing of neutral fermions at conserved spin is considered. Novel phases are found. In external magnetic field the phase with zero mean spin proves to be unstable to the formation of a phase with a non-zero spin. For $H > H_{cr2}$ the spin-triplet pairing and ferromagnetic superfluidity continue to exist above the "old" phase transition critical temperature $T_{cr}$ . For a certain parameter choice ferromagnetic superfluid phases are formed already for $H = 0$ , characterized by an own magnetic field $h$ . Formation of domains is discussed. Next, spin-triplet pairing of charged fermions is studied. Novel phases are found with a ferromagnetic superconductivity. Then, the 3P $_{2}$ $nn$ pairing in neutron star matter is studied. Also a 3P $_{2}$ $pp$ pairing is considered. Numerical estimates are performed in the BCS weak coupling limit and beyond it for the $3 P_{2}$ $nn$ and $pp$ pairings, as well as for the 3S $_{1}$ $n p$ pairing.
nucl-thcond-mat.supr-conhep-phPRD(2020)·6 citations
07
Hydrodynamics from free-streaming to thermalization and back again
Chandrodoy Chattopadhyay🇺🇸 · Ulrich W. Heinz (Ohio State University)🇺🇸
We study the evolution of the Knudsen and Reynolds numbers in (0+1)-dimensionally expanding fluids with Bjorken symmetry for systems whose microscopic mean free path rises more quickly with time than usually assumed. This allows us to explore within a simple 1-dimensional model the transition from initially thermalizing to ultimately decoupling dynamics. In all cases studied the dynamics is found to be controlled by hydrodynamic attractors for both the Knudsen and Reynolds numbers whose trajectories undergo characteristic changes as the dynamics changes from thermalizing to decoupling.
nucl-thhep-phPLB(2020)·49 citations
08
Elastic transfer and parity dependence of the nucleus-nucleus optical potential
Nguyen Tri Toan Phuc · R. S. Mackintosh · Nguyen Hoang Phuc · Dao T. Khoa
Background: A recent coupled reaction channel (CRC) study shows that the enhanced oscillation of the elastic $^{16}$ O+ $^{12}$ C cross section at backward angles is due mainly to the elastic $α$ transfer or the core exchange. Such a process gives rise to a parity-dependent term in the total elastic $S$ -matrix, an indication of the parity dependence of the $^{16}$ O+ $^{12}$ C optical potential (OP). Purpose: To explicitly determine the core exchange potential (CEP) induced by the symmetric exchange of the two $^{12}$ C cores in the elastic $^{16}$ O+ $^{12}$ C scattering at $E_{lab} = 132$ and 300 MeV, and explore its parity dependence. Method: $S$ -matrix generated by CRC description of the elastic $^{16}$ O+ $^{12}$ C scattering is used as the input for the inversion calculation to obtain the effective local OP that contains both the Wigner and Majorana terms. Results: The high-precision inversion results show a strong contribution by the complex Majorana term in the total OP of the $^{16}$ O+ $^{12}$ C system, and thus provide for the first time a direct estimation of the parity-dependent CEP. Conclusions: The elastic $α$ transfer or exchange of the two $^{12}$ C cores in the $^{16}$ O+ $^{12}$ C system gives rise to a complex parity dependence of the total OP. This should be a general feature of the OP for the light heavy-ion systems that contain two identical cores.
nucl-thPRC(2019)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE