Nuclear Theory·nucl-th
11 papers—3 primary·8 cross-listed
These proceedings from the Quark Matter 2017 conference give an overview of the latest experimental results on hard processes in small collision systems at RHIC and the LHC, discuss their implications, and consider several prospects for future measurements.
Richard T. Scherrer🇺🇸 · Robert J. Scherrer🇺🇸
A change in the fundamental constants of nature or plasma effects in the early universe could stabilize Be against decay into two He nuclei. Coc et al. examined this effect on big bang nucleosynthesis as a function of , the mass difference between two He nuclei and a single Be nucleus, and found no effects for keV. Here we examine stable Be with larger and also allow for a variation in the rate for He + He Be to determine the threshold for interesting effects. We find no change to standard big bang nucleosynthesis for MeV. For MeV and a sufficiently large reaction rate, a significant fraction of He is burned into Be, which fissions back into He when assumes its present-day value, leaving the primordial He abundance unchanged. However, this sequestration of He results in a decrease in the primordial Li abundance. Primordial abundances of Li consistent with observationally-inferred values can be obtained for reaction rates similar to those calculated for the present-day (unbound Be) case. Even for the largest binding energies and largest reaction rates examined here, only a small fraction of Be is burned into heavier elements, consistent with earlier studies. There is no change in the predicted deuterium abundance for any model we examined.
P. Alberto · M. Malheiro · T. Frederico · A. de Castro
We propose a generalization of pseudospin and spin symmetries, the SU(2) symmetries of Dirac equation with scalar and vector mean-field potentials originally found independently in the 70's by Smith and Tassie, and Bell and Ruegg. As relativistic symmetries, they have been extensively researched and applied to several physical systems for the last 18 years. The main feature of these symmetries is the suppression of the spin-orbit coupling either in the upper or lower components of the Dirac spinor, thereby turning the respective second-order equations into Schrödinger-like equations, i.e, without a matrix structure. In this paper we use the original formalism of Bell and Ruegg to derive general requirements for the Lorentz structures of potentials in order to have these SU(2) symmetries in the Dirac equation, again allowing for the suppression of the matrix structure of the second-order equation of either the upper or lower components of the Dirac spinor. Furthermore, we derive equivalent conditions for spin and pseudospin symmetries with 2- and 1-dimensional potentials and list some possible candidates for 3, 2, and 1 dimensions. We suggest applications for physical systems in three and two dimensions, namely electrons in graphene.
In the lightly bound Skyrme model, several Skyrmions having particularly strong binding are clusters of unit baryon number Skyrmions arranged as truncated tetrahedra. Their baryon numbers form the sequence B = 4, 16, 40, 80, 140, 224. This is the standard sequence of tetrahedral numbers multiplied by four, and therefore agrees with the sequence of magic proton and neutron numbers 2, 8, 20, 40, 70, 112 that occurs in the nuclear shell model in the absence of strong spin-orbit coupling. This sequence includes several of the magic numbers that are predicted for tetrahedrally deformed nuclei, and also appears in the context of the FCC lattice geometry investigated long ago by Wigner and revived more recently.
José Guilherme Milhano🇵🇹 · Urs Achim Wiedemann🇨🇭 · Korinna Christine Zapp🇵🇹
Jet quenching in heavy ion collisions is expected to be accompanied by recoil effects, but unambiguous signals for the induced medium response have been difficult to identify so far. Here, we argue that modern jet substructure measurements can improve this situation qualitatively since they are sensitive to the momentum distribution inside the jet. We show that the groomed subjet shared momentum fraction , and the girth of leading and subleading subjets signal recoil effects with dependencies that are absent in a recoilless baseline. We find that recoil effects can explain most of the medium modifications to the distribution observed in data. Furthermore, for jets passing the Soft Drop Condition, recoil effects induce in the differential distribution of subjet separation a characteristic increase with , and they introduce a characteristic enhancement of the girth of the subleading subjet with decreasing . We explain why these qualitatively novel features, that we establish in \textsc{Jewel+Pythia} simulations, reflect generic physical properties of recoil effects that should therefore be searched for as telltale signatures of jet-induced medium response.
B. J. Roy · Y. Sawant · P. Patwari · S. Santra · A. Pal · A. Kundu · D. Chattopadhyay · V. Jha · S. K. Pandit · V. V. Parkar · K. Ramachandran · K. Mahata and 7 other authors
The reaction mechanism of deep-inelastic multinucleon transfer processes in the O+Al reaction at an incident O energy ( MeV) substantially above the Coulomb barrier has been studied both experimentally and theoretically. Elastic-scattering angular distribution, total kinetic energy loss spectra and angular distributions for various transfer channels have been measured. The -value- and angle-integrated isotope production cross sections have been deduced. To obtain deeper insight into the underlying reaction mechanism, we have carried out a detailed analysis based on the time-dependent Hartree-Fock (TDHF) theory. A recently developed method, TDHF+GEMINI, has been applied to evaluate production cross sections for secondary products. From a comparison between the experimental and theoretical cross sections, we find that the theory qualitatively reproduces the experimental data. Significant effects of secondary light-particle emissions are demonstrated. Possible interplay between fusion-fission, deep-inelastic, multinucleon transfer and particle evaporation processes are discussed.
Sašo Grozdanov🇳🇱 · Napat Poovuttikul🇳🇱
We begin the exploration of holographic duals to theories with generalised global (higher-form) symmetries. In particular, we focus on the case of magnetohydrodynamics (MHD) in strongly coupled plasmas by constructing and analysing a holographic dual to a recent, generalised global symmetry-based formulation of dissipative MHD. The simplest holographic dual to the effective theory of MHD that was proposed as a description of plasmas with any equation of state and transport coefficients contains dynamical graviton and two-form gauge field fluctuations in a magnetised black brane background. The dual field theory, which is closely related to the large-, supersymmetric Yang-Mills theory at (infinitely) strong coupling, is, as we argue, in our setup coupled to a dynamical gauge field with a renormalisation condition-dependent electromagnetic coupling. After constructing the holographic dictionary for gauge-gravity duals of field theories with higher-form symmetries, we compute the dual equation of state and transport coefficients, and for the first time analyse phenomenology of MHD waves in a strongly interacting, dense plasma with a (holographic) microscopic description. From weak to extremely strong magnetic fields, several predictions for the behaviour of Alfvén and magnetosonic waves are discussed.
The operator of time formalism is applied to radioactive decay. It appears that the proposed approach offers better insight and understanding of the phenomena in a way that the decay exponential-law becomes the Boltzmann distribution in Gibbs treatment of canonical ensemble. The radioactive decay is seen as temporal canonical ensemble where the radioactive constant appears as the analog of the absolute temperature multiplied by Boltzmann constant. The stochastic character of decay process becomes plausible in the proposed approach and the explanation why decay is characterized by constant, and not by some parameter, is offered.
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