Nuclear Theory·nucl-th

Friday·September 25, 2020

14 papers—8 primary·6 cross-listed

01
Consistent description of angular correlations in $β$ decay for Beyond Standard Model physics searches
Leendert Hayen🇺🇸 · Albert R. Young🇺🇸
Measurements of angular correlations between initial and final particles in $β$ decay remain one of the most promising ways of probing the Standard Model and looking for new physics. As experiments reach unprecedented precision well into the per-mille regime, proper extraction of results requires one to take into account a great number of nuclear structure and radiative corrections in a procedure which becomes dependent upon the experimental geometry. We provide here a compilation and update of theoretical results which describe all corrections in the same conceptual framework, point out pitfalls and review the influence of the experimental geometry. Finally, we summarize the potential for new physics reach.
nucl-thnucl-ex22 citations
02
Proximity effect of pair correlation in the inner crust of neutron stars
Toshiyuki Okihashi · Masayuki Matsuo
We study proximity effect of pair correlation in the inner crust of neutron stars by means of the Skyrme-Hartree-Fock-Bogoliubov theory formulated in the coordinate space. We describe a system composed of a nuclear cluster immersed in neutron superfluid, which is confined in a spherical box. Using a density-dependent effective pairing interaction which reproduces both the pair gap of neutron matter obtained in ab initio calculations and that of finite nuclei, we analyze how the pair condensate in neutron superfluid is affected by the presence of the nuclear cluster. It is found that the proximity effect is characterized by the coherence length of neutron superfluid measured from the edge position of the nuclear cluster. The calculation predicts that the proximity effect has a strong density dependence. In the middle layers of the inner crust with baryon density $5 \times 1 0^{- 4}$ fm $^{- 3} < ρ_{b} < 2 \times 1 0^{- 2}$ fm $^{- 3}$ , the proximity effect is well limited in the vicinity of the nuclear cluster, i.e. in a sufficiently smaller area than the Wigner-Seitz cell. On the contrary, the proximity effect is predicted to extend to the whole volume of the Wigner-Seitz cell in shallow layers of the inner crust with $ρ_{b} < 2 \times 1 0^{- 4}$ fm $^{- 3}$ , and in deep layers with $ρ_{b} > 5 \times 1 0^{- 2}$ fm $^{- 3}$ .
nucl-thPTEP(2021)·8 citations
03
Magnetic field effect on pion superfluid
Shijun Mao🇨🇳
Magnetic field effect on pion superfluid phase transition is investigated in frame of a Pauli-Villars regularized NJL model. Instead of directly dealing with charged pion condensate, we apply the Goldstone's theorem (massless Goldstone boson $π^{+}$ ) to determine the onset of pion superfluid phase, and obtain the phase diagram in magnetic field, temperature, isospin and baryon chemical potential space. At weak magnetic field, it is analytically proved that the critical isospin chemical potential of pion superfluid phase transition is equal to the mass of $π^{+}$ meson in magnetic field. The pion superfluid phase is retarded to higher isospin chemical potential, and can survive at higher temperature and higher baryon chemical potential under external magnetic field.
nucl-thhep-phPRD(2020)·6 citations
04
Dynamical energy loss formalism: from describing suppression patterns to implications for future experiments
Magdalena Djordjevic🇷🇸 · Dusan Zigic🇷🇸 · Bojana Blagojevic🇷🇸 · Jussi Auvinen🇷🇸 · Igor Salom🇷🇸 · Marko Djordjevic🇷🇸
Understanding properties of Quark-Gluon Plasma requires an unbiased comparison of experimental data with theoretical predictions. To that end, we developed the dynamical energy loss formalism which, in distinction to most other methods, takes into account a realistic medium composed of dynamical scattering centers. The formalism also allows making numerical predictions for a wide number of observables with the same parameter set fixed to standard literature values. In this proceedings, we overview our recently developed DREENA-C and DREENA-B frameworks, where DREENA is a computational implementation of the dynamical energy loss formalism, and where C stands for constant temperature QCD medium, while B stands for the medium modeled by 1+1D Bjorken expansion. At constant temperature our predictions overestimate $v_{2}$ , in contrast to other models, but consistent with simple analytical estimates. With Bjorken expansion, we have a good agreement of the predictions with both $R_{AA}$ and $v_{2}$ measurements. We find that introducing medium evolution has a larger effect on $v_{2}$ predictions, but for precision predictions it has to be taken into account in $R_{AA}$ predictions as well. Based on numerical calculations and simple analytical derivations, we also propose a new observable, which we call path length sensitive suppression ratio, for which we argue that the path length dependence can be assessed in a straightforward manner. We also argue that $P b + P b$ vs. $X e + X e$ measurements make a good system to assess the path length dependence. As an outlook, we expect that introduction of more complex medium evolution (beyond Bjorken expansion) in the dynamical energy loss formalism can provide a basis for a state of the art QGP tomography tool - e.g. to jointly constrain the medium properties from the point of both high pt and low pt data.
nucl-thhep-phNPA(2019)·3 citations
05
Structure of the quartetting ground state of $N = Z$ nuclei
A. G. Serban · D. R. Nichita · D. Negrea · V. V. Baran
The formal equivalence between the quartetting picture and the symmetry restored BCS picture is established for the ground state correlations induced by the general isovector-isoscalar pairing interaction. Multiple ground state structures compatible with the particle number and isospin symmetries are evaluated. The competition of isovector and isoscalar correlations is discussed for the $N = Z$ nuclei above $^{100}$ Sn.
nucl-thEPJA(2021)·2 citations
06
Complete experiments in pseudoscalar meson photoproduction
Yannick Wunderlich
The problem of extracting photoproduction amplitudes uniquely from so called complete experiments is discussed. This problem can be considered either for the extraction of full production amplitudes, or for the determination of multipoles. Both cases are treated briefly. Preliminary results for the fitting of multipoles, as well as the determination of their error, from recent polarization measurements in the $Δ$ -region are described in more detail.
nucl-thBled Workshops Phys.(2015)·0 citations
07
Mathematical aspects of phase rotation ambiguities in partial wave analyses
Yannick Wunderlich
The observables in a single-channel $2$ -body scattering problem remain invariant once the amplitude is multiplied by an overall energy- and angle-dependent phase. This invariance is known as the continuum ambiguity. Also, mostly in truncated partial wave analyses (TPWAs), discrete ambiguities originating from complex conjugation of roots are known to occur. In this note, it is shown that the general continuum ambiguity mixes partial waves and that for scalar particles, discrete ambiguities are just a subset of continuum ambiguities with a specific phase. A numerical method is outlined briefly, which can determine the relevant connecting phases.
nucl-thBled Workshops Phys.(2017)·0 citations
08
Dilepton production in microscopic transport theory with in-medium $ρ$ -meson spectral function
A.B. Larionov🇩🇪 · U. Mosel🇩🇪 · L. von Smekal🇩🇪
We use the microscopic GiBUU transport model to calculate dilepton ( $e^{+} e^{-}$ ) production in heavy-ion collisions at SIS18 energies focusing on the effect of collisional broadening of the $ρ$ -meson. The collisional width of the $ρ$ -meson at finite temperature and baryon density in nuclear matter is calculated on the basis of the collision integral of the GiBUU model. A systematic comparison with HADES data on dilepton production in heavy-ion collisions is performed. The collisional broadening of the $ρ$ improves the agreement between theory and experiment for the dilepton invariant-mass distributions near the $ρ$ pole mass and for the excess radiation in Au+Au at $1.23 A$ GeV. We furthermore show that some remaining underprediction of the experimental dilepton spectra in C+C at $1 A$ GeV and Au+Au at $1.23 A$ GeV at intermediate invariant masses $0.2 - 0.4$ GeV can be accounted for by adjusting the $p n$ bremsstrahlung cross section in a way to agree with the inclusive dilepton spectrum from $d p$ collisions at $1.25 A$ GeV.
nucl-thhep-exhep-phnucl-exPRC(2021)·20 citations
09
Contact interaction analysis of pion GTMDs
Jin-Li Zhang🇨🇳 · Zhu-Fang Cui🇨🇳 · Jia-Lun Ping🇨🇳 · Craig D. Roberts🇨🇳
A contact interaction is used to calculate an array of pion twist-two, -three and -four generalised transverse light-front momentum dependent parton distribution functions (GTMDs). Despite the interaction's simplicity, many of the results are physically relevant, amongst them a statement that GTMD size and shape are largely prescribed by the scale of emergent hadronic mass. Moreover, proceeding from GTMDs to generalised parton distributions (GPDs), it is found that the pion's mass distribution form factor is harder than its electromagnetic form factor, which is harder than the gravitational pressure distribution form factor; the pressure in the neighbourhood of the pion's core is commensurate with that at the centre of a neutron star; the shear pressure is maximal when confinement forces become dominant within the pion; and the spatial distribution of transversely polarised quarks within the pion is asymmetric. Regarding transverse momentum dependent distribution functions (TMDs), their magnitude and domain of support decrease with increasing twist. The simplest Wigner distribution associated with the pion's twist-two dressed-quark GTMD is sharply peaked on the kinematic domain associated with valence-quark dominance; has a domain of negative support; and broadens as the transverse position variable increases in magnitude.
↳ hep-phhep-exhep-latnucl-ex+1EPJC(2021)·60 citations
10
First-Order General-Relativistic Viscous Fluid Dynamics
Fabio S. Bemfica🇧🇷 · Marcelo M. Disconzi🇺🇸 · Jorge Noronha🇺🇸
We present the first generalization of Navier-Stokes theory to relativity that satisfies all of the following properties: (a) the system coupled to Einstein's equations is causal and strongly hyperbolic; (b) equilibrium states are stable; (c) all leading dissipative contributions are present, i.e., shear viscosity, bulk viscosity, and thermal conductivity; (d) non-zero baryon number is included; (e) entropy production is non-negative in the regime of validity of the theory; (f) all of the above holds in the nonlinear regime without any simplifying symmetry assumptions. These properties are accomplished using a generalization of Eckart's theory containing only the hydrodynamic variables, so that no new extended degrees of freedom are needed as in Müller-Israel-Stewart theories. Property (b), in particular, follows from a more general result that we also establish, namely, sufficient conditions that when added to stability in the fluid's rest frame imply stability in any reference frame obtained via a Lorentz transformation. All our results are mathematically rigorously established. The framework presented here provides the starting point for systematic investigations of general-relativistic viscous phenomena in neutron star mergers.
↳ gr-qchep-phhep-thnucl-thPRX(2022)·237 citations
11
Chiral vortical effect for vector fields
G. Yu. Prokhorov🇷🇺 · O.V. Teryaev🇷🇺 · V.I. Zakharov🇷🇺
We consider photonic vortical effect, i.e. the difference of the flows of left- and right-handed photons along the vector of angular velocity in rotating photonic medium. Two alternative frameworks to evaluate the effect are considered, both of which have already been tried in the literature. First, the standard thermal fied theory and, alternatively, Hawking-radiation-type derivation. In our earlier attempt to compare the two approaches, we found a crucial factor of two difference. Here we revisit the problem, paying more attention to details of infrared regularizations. We find out that introduction of an infinitesimal mass of the vector field brings the two ways of evaluating the chiral vortical effect into agreement with each other. Some implications, both on the theoretical and phenomenological sides, are mentioned.
↳ hep-thhep-phnucl-thPRD(2021)·16 citations
12
Theoretical Analysis of Antineutron-Nucleus Data needed for Antineutron Mirrors in Neutron-Antineutron Oscillation Experiments
K.V. Protasov🇫🇷 · V. Gudkov🇺🇸 · E. A. Kupriyanova🇷🇺 · V.V.Nesvizhevsky🇫🇷 · W.M. Snow🇺🇸 · A.Yu. Voronin🇷🇺
The values of the antineutron-nucleus scattering lengths, and in particular their imaginary parts, are needed to evaluate the feasibility of using neutron mirrors in laboratory experiments to search for neutron-antineutron oscillations. We analyze existing experimental and theoretical constraints on these values with emphasis on low $A$ nuclei and use the results to suggest materials for the neutron/antineutron guide and to evaluate the systematic uncertainties in estimating the neutron-antineutron oscillation time. As an example we discuss a scenario for a future neutron-antineutron oscillation experiment proposed for the European Spallation Source. We also suggest future experiments which can provide a better determination of the values of antineutron-nuclei scattering lengths.
↳ hep-phnucl-exnucl-thPRD(2020)·18 citations
13
Search for Efficient Formulations for Hamiltonian Simulation of non-Abelian Lattice Gauge Theories
Zohreh Davoudi🇺🇸 · Indrakshi Raychowdhury🇺🇸 · Andrew Shaw🇺🇸
Hamiltonian formulation of lattice gauge theories (LGTs) is the most natural framework for the purpose of quantum simulation, an area of research that is growing with advances in quantum-computing algorithms and hardware. It, therefore, remains an important task to identify the most accurate, while computationally economic, Hamiltonian formulation(s) in such theories, considering the necessary truncation imposed on the Hilbert space of gauge bosons with any finite computing resources. This paper is a first step toward addressing this question in the case of non-Abelian LGTs, which further require the imposition of non-Abelian Gauss's laws on the Hilbert space, introducing additional computational complexity. Focusing on the case of SU(2) LGT in 1+1 D coupled to matter, a number of different formulations of the original Kogut-Susskind framework are analyzed with regard to the dependence of the dimension of the physical Hilbert space on boundary conditions, system's size, and the cutoff on the excitations of gauge bosons. The impact of such dependencies on the accuracy of the spectrum and dynamics is examined, and the (classical) computational-resource requirements given these considerations are studied. Besides the well-known angular-momentum formulation of the theory, the cases of purely fermionic and purely bosonic formulations (with open boundary conditions), and the Loop-String-Hadron formulation are analyzed, along with a brief discussion of a Quantum Link Model of the same theory. Clear advantages are found in working with the Loop-String-Hadron framework which implements non-Abelian Gauss's laws a priori using a complete set of gauge-invariant operators. Although small lattices are studied in the numerical analysis of this work, and only the simplest algorithms are considered, a range of conclusions will be applicable to larger systems and potentially to higher dimensions.
↳ hep-lathep-phnucl-thquant-phPRD(2021)·164 citations
14
Two-nucleon S-wave interactions at the $S U (3)$ flavor-symmetric point with $m_{u d} ≃ m_{s}^{phys}$ : a first lattice QCD calculation with the stochastic Laplacian Heaviside method
Ben Hörz🇺🇸 · Dean Howarth🇺🇸 · Enrico Rinaldi🇯🇵 · Andrew Hanlon🇩🇪 · Chia Cheng Chang🇯🇵 · Christopher Körber🇩🇪 · Evan Berkowitz🇺🇸 · John Bulava🇩🇰 · M.A. Clark🇺🇸 · Wayne Tai Lee🇺🇸 · Colin Morningstar🇺🇸 · Amy Nicholson🇺🇸 · Pavlos Vranas🇺🇸 · André Walker-Loud🇺🇸
We report on the first application of the stochastic Laplacian Heaviside method for computing multi-particle interactions with lattice QCD to the two-nucleon system. Like the Laplacian Heaviside method, this method allows for the construction of interpolating operators which can be used to construct a positive definite set of two-nucleon correlation functions, unlike nearly all other applications of lattice QCD to two nucleons in the literature. It also allows for a variational analysis in which optimal linear combinations of the interpolating operators are formed that couple predominantly to the eigenstates of the system. Utilizing such methods has become of paramount importance in order to help resolve the discrepancy in the literature on whether two nucleons in either isospin channel form a bound state at pion masses heavier than physical, with the discrepancy persisting even in the $S U (3)$ -flavor symmetric point with all quark masses near the physical strange quark mass. This is the first in a series of papers aimed at resolving this discrepancy. In the present work, we employ the stochastic Laplacian Heaviside method without a hexaquark operator in the basis at a lattice spacing of $a \sim 0.086$ ~fm, lattice volume of $L = 48 a ≃ 4.1$ ~fm and pion mass $m_{π} ≃ 714$ MeV. With this setup, the observed spectrum of two-nucleon energy levels strongly disfavors the presence of a bound state in either the deuteron or dineutron channel.
↳ hep-lathep-phnucl-exnucl-thPRC(2021)·93 citations

Affiliations

first authorsco-authorsvia INSPIRE