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Nuclear Theory·nucl-th

Monday·May 18, 2020

6 papers—2 primary·4 cross-listed

All6Primary2Cross-lists4
  1. 01

    Quartet condensation induced by the isovector pairing force

    M. Sambataro · N. Sandulescu

    The phenomenon of quartet condensation in the ground state of an isovector pairing Hamiltonian for an even-even system is investigated. For this purpose we follow the evolution of the ground state from an unperturbed regime up to a strongly interacting one in a formalism of collective pairs. These pairs are those resulting from the diagonalization of the pairing Hamiltonian in a space of two particles coupled to isospin . The ground state is found to rapidly evolve from a product of distinct quartets, each one formed by two of the above pairs, to a condensate of identical quartets built only with the pair corresponding to the lowest energy. This finding establishes a link between the complicated structure of the exact ground state and the simple approximation scheme of the Quartet Condensation Model. The mechanism at the basis of this quartet condensation turns out to be the same which is responsible for the development of a pair condensate in the ground state of a like-particle pairing Hamiltonian.

    nucl-thJ.Phys.G(2020)·1 citation
  2. 02

    Subleading contributions to the nuclear scalar isoscalar currents

    Hermann Krebs🇩🇪 · Evgeny Epelbaum🇩🇪 · Ulf-G. Meißner🇩🇪

    We extend our recent analyses of the nuclear vector, axial-vector and pseudoscalar currents and derive the leading one-loop corrections to the two-nucleon scalar current operator in the framework of chiral effective field theory using the method of unitary transformation. We also show that the scalar current operators at zero momentum transfer are directly related to the quark mass dependence of the nuclear forces.

    nucl-thhep-phEPJA(2020)·15 citations
  3. 03

    Scattering using real-time path integrals

    W. N. Polyzou🇺🇸 · Ekaterina Nathanson🇺🇸

    Background: Path integrals are a powerful tool for solving problems in quantum theory that are not amenable to a treatment by perturbation theory. Most path integral computations require an analytic continuation to imaginary time. While imaginary time treatments of scattering are possible, imaginary time is not a natural framework for treating scattering problems. Purpose: To test a recently introduced method for performing direct calculations of scattering observables using real-time path integrals. Methods: The computations are based on a new interpretation of the path integral as the expectation value of a potential functional on a space of continuous paths with respect to a complex probability distribution. The method has the advantage that it can be applied to arbitrary short-range potentials. Results: The new method is tested by applying it to calculate half-shell sharp-momentum transition matrix elements for one-dimensional potential scattering. The calculations for half shell transition operator matrix elements are in agreement with a numerical solution of the Lippmann-Schwinger equation. The computational method has a straightforward generalization to more complicated systems.

    ↳ nucl-thhep-lathep-thPRC(2020)·4 citations
  4. 04

    Bayesian Inference of the Symmetry Energy of Super-Dense Neutron-Rich Matter from Future Radius Measurements of Massive Neutron Stars

    Wen-Jie Xie🇨🇳 · Bao-An Li🇺🇸

    Using an explicitly isospin-dependent parametric Equation of State (EOS) for the core of neutron stars (NSs) within the Bayesian statistical approach, we infer the EOS parameters of super-dense neutron-rich nuclear matter from three sets of imagined mass-radius correlation data representing typical predictions by various nuclear many-body theories, i.e, the radius stays the same, decreases or increases with increasing NS mass within between 1.4 M and 2.0 M. The corresponding average density increases quickly, slowly or slightly decreases as the NS mass increases from 1.4 M to 2.0 M. Using the posterior probability distribution functions (PDFs) of EOS parameters inferred from GW170817 and NICER radius data for canonical NSs as references, we investigate how future radius measurements of massive NS will improve our knowledge about the EOS of super-dense neutron-rich nuclear matter, especially its symmetry energy term, compared to what people have already learned from analyzing the GW170817 and NICER data. While the EOS of symmetric nuclear matter (SNM) inferred from the three data sets are approximately the same, the corresponding high-density symmetry energies at densities above about are very different, indicating that the radii of massive NSs carry reliable information about the high-density behavior of nuclear symmetry energy with little influence from the remaining uncertainties of the SNM EOS.

    ↳ astro-ph.HEnucl-exnucl-thApJ(2020)·96 citations
  5. 05

    Helicity at Small : Oscillations Generated by Bringing Back the Quarks

    Yuri V. Kovchegov🇺🇸 · Yossathorn Tawabutr🇺🇸

    We construct a numerical solution of the recently-derived large- small- helicity evolution equations with the aim to establish the small- asymptotics of the quark helicity distribution beyond the large- limit explored previously in the same framework. (Here and are the numbers of quark colors and flavors.) While the large- helicity evolution involves gluons only, the large- evolution includes contributions from quarks as well. We find that adding quarks to the evolution makes quark helicity distribution oscillate as a function of . Our numerical results in the large- limit lead to the -dependence of the flavor-singlet quark helicity distribution which is well-approximated by \begin{align} \Delta \Sigma (x, Q^2)\bigg|_{\mbox{large-}N_c \& N_f} \sim \left( \frac{1}{x} \right)^{\alpha_h^q} \, \cos \left[ \omega_q \, \ln \left( \frac{1}{x} \right) + \varphi_q \right]. \end{align} The power exhibits a weak -dependence, and, for all values considered, remains very close to obtained earlier in the large- limit. The novel oscillation frequency and phase shift depend more strongly on the number of flavors (with in the pure-glue large- limit). The typical period of oscillations for is rather long, spanning many units of rapidity. We speculate whether the oscillations we find are related to the sign variation with seen in the strange quark helicity distribution extracted from the data.

    ↳ hep-phhep-exnucl-exnucl-thJHEP(2020)·57 citations
  6. 06

    Tagging boosted hadronic objects with dynamical grooming

    Yacine Mehtar-Tani🇺🇸 · Alba Soto-Ontoso🇺🇸 · Konrad Tywoniuk🇳🇴

    We evaluate the phenomenological applicability of the dynamical grooming technique, introduced in [1], to boosted W and top tagging at LHC conditions. An extension of our method intended for multi-prong decays with an internal mass scale, such as the top quark decay, is presented. First, we tackle the reconstruction of the mass distribution of W and top jets quantifying the smearing due to pileup. When compared to state-of-the-art grooming algorithms like SoftDrop and its recursive version, dynamical grooming shows an enhanced resilience to background fluctuations. In addition, we asses the discriminating power of dynamical grooming to distinguish W (top) jets from QCD ones by performing a two-step analysis: introduce a cut on the groomed mass around the W (top) mass peak followed by a restriction on the N-subjettinnes ratio (). For W jets, the out-of-the-box version of dynamical grooming, free of ad-hoc parameters, results into a comparable performance to SoftDrop. Regarding the top tagger efficiency, 3-prong dynamical grooming, in spite of its simplicity, presents better performance than SoftDrop and similar results to Recursive SoftDrop.

    ↳ hep-phhep-exnucl-exnucl-thPRD(2020)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE