Nuclear Theory·nucl-th

Monday·July 13, 2020

14 papers—8 primary·6 cross-listed

09
$QQ s ˉ s ˉ$ tetraquarks in the chiral quark model
Gang Yang🇨🇳 · Jialun Ping🇨🇳 · Jorge Segovia🇪🇸
The low-lying $S$ -wave $QQ s ˉ s ˉ$ ( $Q = c, b$ ) tetraquark states with $I J^{P} = 0 0^{+}$ , $0 1^{+}$ and $0 2^{+}$ are systematically investigated in the framework of complex scaling range of chiral quark model. Every structure including meson-meson, diquark-antidiquark and K-type configurations, and all possible color channels in four-body sector are considered by means of a commonly extended variational approach, Gaussian expansion method. Several narrow and wide resonance states are obtained for $cc s ˉ s ˉ$ and $bb s ˉ s ˉ$ tetraquarks with $I J^{P} = 0 0^{+}$ and $0 2^{+}$ . Meanwhile, narrow resonances for $c b s ˉ s ˉ$ tetraquarks are also found in $I J^{P} = 0 0^{+}$ , $0 1^{+}$ and $0 2^{+}$ states. These results confirm the possibility of finding hadronic molecules with masses $\sim 0.6 GeV$ above the noninteracting hadron-hadron thresholds.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2020)·36 citations
10
Charge Distributions of Moving Nucleons
Cédric Lorcé (Ecole Polytechnique, CPHT)🇫🇷
Relativistic charge distributions of targets with arbitrary average momentum are introduced. They provide an interpolation between the usual Breit frame and infinite-momentum frame distributions. We find that Breit frame distributions can be interpreted from a phase-space perspective as internal charge quasi-densities in the rest frame of a localized target, without any relativistic correction. We show also that the apparent discrepancies between Breit frame and infinite-momentum frame distributions simply result from kinematical artifacts associated with spin.
↳ hep-phnucl-thPRL(2020)·88 citations
11
On the nature of near-threshold bound and virtual states
Inka Matuschek🇩🇪 · Vadim Baru🇩🇪 · Feng-Kun Guo🇨🇳 · Christoph Hanhart🇩🇪
Physical states are characterised uniquely by their pole positions and the corresponding residues. Accordingly, in those parameters also the nature of the states should be encoded. For bound states (poles on the real $s$ -axis below the lowest threshold on the physical sheet) there is an established criterion formulated originally by Weinberg in the 1960s, which allows one to estimate the amount of compact and molecular components in a given state. We demonstrate in this paper that this criterion can be straightforwardly extended to shallow virtual states (poles on the real $s$ -axis below the lowest threshold on the unphysical sheet) which should be classified as molecular. We argue that predominantly non-molecular or compact states exist either as bound states or as resonances (poles on the unphysical sheet off the real energy axis) but not as virtual states. We also discuss the limitations of the mentioned classification scheme.
↳ hep-phhep-exhep-latnucl-thEPJA(2021)·116 citations
12
Complex Paths Around The Sign Problem
Andrei Alexandru🇺🇸 · Gokce Basar🇺🇸 · Paulo F. Bedaque🇺🇸 · Neill C. Warrington🇺🇸
The Monte Carlo evaluation of path integrals is one of a few general purpose methods to approach strongly coupled systems. It is used in all branches of Physics, from QCD/nuclear physics to the correlated electron systems. However, many systems of great importance (dense matter inside neutron stars, the repulsive Hubbard model away from half-filling, dynamical and non-equilibrium observables) are not amenable to the Monte Carlo method as it currently stands due to the so-called "sign-problem". We review a new set of ideas recently developed to tackle the sign problem based on the complexification of field space and the Picard-Lefshetz theory accompanying it. The mathematical ideas underpinning this approach, as well as the algorithms so far developed, are described together with non-trivial examples where the method has already been proved successful. Directions of future work, including the burgeoning use of machine learning techniques, are delineated.
↳ hep-latcond-mat.str-elhep-thnucl-th+1RMP(2022)·186 citations
13
Hydrodynamic gradient expansion in linear response theory
Michal P. Heller🇩🇪 · Alexandre Serantes🇫🇮 · Michał Spaliński🇵🇱 · Viktor Svensson🇩🇪 · Benjamin Withers🇬🇧
A foundational question in relativistic fluid mechanics concerns the properties of the hydrodynamic gradient expansion at large orders. We establish the precise conditions under which this gradient expansion diverges for a broad class of microscopic theories admitting a relativistic hydrodynamic limit, in the linear regime. Our result does not rely on highly symmetric fluid flows utilized by previous studies of heavy-ion collisions and cosmology. The hydrodynamic gradient expansion diverges whenever energy density or velocity fields have support in momentum space exceeding a critical momentum, and converges otherwise. This critical momentum is an intrinsic property of the microscopic theory and is set by branch point singularities of hydrodynamic dispersion relations.
↳ hep-thhep-phnucl-thphysics.flu-dynPRD(2021)·61 citations
14
GW190814: Spin and equation of state of a neutron star companion
Antonios Tsokaros · Milton Ruiz · Stuart L. Shapiro
The recent discovery by LIGO/Virgo of a merging binary having a $\sim 23 M_{⊙}$ black hole and a $\sim 2.6 M_{⊙}$ compact companion has triggered a debate regarding the nature of the secondary, which falls into the so-called mass gap. Here we explore some consequences of the assumption that the secondary was a neutron star (NS). We show with concrete examples of heretofore viable equations of state (EOSs) that rapid uniform rotation may neither be necessary for some EOSs nor sufficient for others to explain the presence of a NS. Absolute upper limits for the maximum mass of a spherical NS derived from GW170817 already suggest that this unknown compact companion might be a slowly or even a nonrotating NS. However several soft NS EOSs favored by GW170817 with maximum spherical masses $≲ 2.1 M_{⊙}$ cannot be invoked to explain this object, even allowing for maximum uniform rotation. By contrast, sufficiently stiff EOSs that yield $2.6 M_{⊙}$ NSs which are slowly rotating or, in some cases, nonrotating, and are compatible with GW170817 and the results of NICER, can account for the black hole companion.
↳ astro-ph.HEgr-qcnucl-thApJ(2020)·97 citations

Affiliations

first authorsco-authorsvia INSPIRE

QQsˉsˉ tetraquarks in the chiral quark model

Charge Distributions of Moving Nucleons

On the nature of near-threshold bound and virtual states

Complex Paths Around The Sign Problem

Hydrodynamic gradient expansion in linear response theory

GW190814: Spin and equation of state of a neutron star companion

Affiliations

$QQ s ˉ s ˉ$ tetraquarks in the chiral quark model