Nuclear Theory·nucl-th

Tuesday·April 30, 2019

14 papers—7 primary·7 cross-listed

08
Short Range Operator Contributions to $0 ν β β$ decay from LQCD
Henry Monge-Camacho🇺🇸 · Evan Berkowitz🇩🇪 · David Brantley🇺🇸 · Chia Cheng Chang🇯🇵 · M.A. Clark🇺🇸 · Arjun Gambhir🇺🇸 · Nicolas Garrón🇬🇧 · Bálint Joó🇺🇸 · Thorsten Kurth🇺🇸 · Amy Nicholson🇺🇸 · Enrico Rinaldi🇺🇸 · Brian Tiburzi🇺🇸 · Pavlos Vranas🇺🇸 · André Walker-Loud🇺🇸
The search for neutrinoless double beta decay of nuclei is believed to be one of the most promising means to search for new physics. Observation of this very rare nuclear process, which violates Lepton Number conservation, would imply the neutrino sector has a Majorana mass component and may also provide an explanation for the universe matter-antimatter asymmetry of the universe. In the case where a heavy intermediate particle is exchanged in this process, QCD contributions from short range interactions become relevant and the calculation of matrix elements with four-quark operators becomes necessary. In these proceedings we will discuss our current progress in the calculation of these four-quark operators from LQCD.
↳ hep-latnucl-thPoS(2019)·4 citations
09
Neutron skins of atomic nuclei: per aspera ad astra
M. Thiel · C. Sfienti · J. Piekarewicz · C.J. Horowitz · M. Vanderhaeghen
The complex nature of the nuclear forces generates a broad range and diversity of observational phenomena. Heavy nuclei, though orders of magnitude less massive than neutron stars, are governed by the same underlying physics, which is enshrined in the nuclear equation of state. Heavy nuclei are expected to develop a neutron-rich skin where many neutrons collect near the surface. Such a skin thickness is strongly sensitive to the poorly-known density dependence of the symmetry energy near saturation density. An accurate and model-independent determination of the neutron-skin thickness of heavy nuclei would provide a significant first constraint on the density dependence of the nuclear symmetry energy. The determination of the neutron-skin thickness of heavy nuclei has far reaching consequences in many areas of physics as diverse as heavy-ion collisions, polarized electron and proton scattering off nuclei, precision tests of the standard model using atomic parity violation, and nuclear astrophysics. While a systematic and concerted experimental effort has been made to measure the neutron-skin thickness of heavy nuclei, a precise and model-independent determination remains elusive. How to move forward at a time when many new facilities are being commissioned and how to strengthen the synergy with other areas of physics are primary goals of this review.
↳ nucl-exastro-ph.HEnucl-thJ.Phys.G(2019)·150 citations
10
Testing the tetraquark mixing framework from QCD sum rules for $a_{0} (980)$
Hee-Jung Lee🇰🇷 · K. S. Kim🇰🇷 · Hungchong Kim🇰🇷
According to a recent proposal of the tetraquark mixing framework, the two light-meson nonets in the $J^{P} = 0^{+}$ channel, namely the light nonet composed of $a_{0} (980)$ , $K_{0}^{*} (800)$ , $f_{0} (500)$ , $f_{0} (980)$ , and the heavy nonet of $a_{0} (1450)$ , $K_{0}^{*} (1430)$ , $f_{0} (1370)$ , $f_{0} (1500)$ , can be expressed by linear combinations of the two tetraquark types, one type containing the spin-0 diquark and the other with the spin-1 diquark. Among various consequences of this mixing model, one surprising result is that the second tetraquark with the spin-1 diquark configuration is more important for the light nonet. In this work, we report that this result can be supported by the QCD sum rule calculation. In particular, we construct a QCD sum rule for the isovector resonance $a_{0} (980)$ using an interpolating field composed of both tetraquark types and then perform the operator product expansion up to dimension 10 operators. Our sum rule analysis shows that the spin-1 diquark configuration is crucial in generating the $a_{0} (980)$ mass. Also, the mixed correlation function constructed from the two tetraquark types is found to have large strength which seems consistent with what the tetraquark mixing framework is advocating. On the other hand, the correlation function from the interpolating field with the spin-0 diquark configuration alone fails to predict the $a_{0} (980)$ mass mostly by the huge negative contribution from dimension 8 operators.
↳ hep-phhep-exhep-latnucl-thPRD(2019)·18 citations
11
Pion generalized parton distribution from lattice QCD
Jiunn-Wei Chen🇹🇼 · Huey-Wen Lin🇺🇸 · Jian-Hui Zhang🇩🇪
We present the first lattice calculation of the valence-quark generalized parton distribution (GPD) of the pion using the large-momentum effective theory (LaMET) approach. We focus on the zero-skewness limit, where the GPD has a probability-density interpretation in the longitudinal Bjorken $x$ and the transverse impact-parameter distributions. Our calculation is done using clover valence fermions on an ensemble of gauge configurations with $2 + 1 + 1$ flavors (degenerate up/down, strange and charm) of highly improved staggered quarks (HISQ) with lattice spacing $a \approx 0.12$ fm, box size $L \approx 3$ fm and pion mass $m_{π} \approx 310$ MeV. The parton distribution function and the form factor are reproduced as special limits of the GPD as expected. Due to the large errors, this exploratory study does not show a clear preference among different model assumptions about the kinematic dependence of the GPD. To discriminate between these assumptions, future studies using higher-statistics data will be crucial.
↳ hep-lathep-phnucl-thNPB(2020)·127 citations
12
Role of the Symmetry Energy on the Structure of Neutron Stars with Unified Equations of State
Nicolas Chamel🇧🇪 · John Michael Pearson🇨🇦 · Alexander Y. Potekhin🇷🇺 · Anthea F. Fantina🇫🇷 · Camille Ducoin🇫🇷 · Anup Dutta🇮🇳 · Stéphane Goriely🇧🇪 · Loïc Perot🇧🇪
The role of the symmetry energy on the internal constitution and the global structure of a cold nonaccreted neutron star is studied using a set of unified equations of state. Based on the nuclear energy-density functional theory, these equations of state provide a thermodynamically consistent treatment of all regions of the star and were calculated using the four different Brussels-Montreal functionals BSk22, BSk24, BSk25 and BSk26. Our predictions are compared to various constraints inferred from astrophysical observations including the recent detection of the gravitational wave signal GW170817 from a binary neutron-star merger.
↳ astro-ph.HEnucl-thAIP Conf.Proc.(2019)·4 citations
13
A background estimator for jet studies in p+p and A+A collisions
Yacine Mehtar-Tani🇺🇸 · Alba Soto-Ontoso🇺🇸 · Marta Verweij🇺🇸
Experimentally, jet physics studies face an unavoidable task: distinguishing, at the detector level, the particles produced in the hard partonic scattering from the ones created in unrelated soft processes such as pileup interactions in high-luminosity proton-proton scattering or the underlying event in heavy-ion collisions. The fluctuating nature of the background constitutes the main source of uncertainty for any subtraction algorithm. Aiming at mitigating the effect of such fluctuations, we present a new method to estimate the background contribution to the transverse momentum on a jet-by-jet basis. Our approach is based on estimating the median background momentum density stored above a $p_{T}$ -cut applied at the constituent level and an experimentally accessible correction term related to the signal contribution below the cut. This allows to trade part of the uncertainty due to background contamination for that of the signal below the cut, similarly to SoftKiller method. We propose to reduce the fluctuations of the latter by exploiting intrinsic correlations among the soft and hard sectors of QCD jets. Our data-driven approach is tested against PYTHIA8 and JEWEL di-jet events embedded in a thermal background and compared to the area-median and SoftKiller methods. The main result of this study is a $\sim 5 - 40%$ improvement on the resolution of the reconstructed jet $p_{T}$ compared to previous methods in a high-luminosity proton-proton scenario. Its applicability in a heavy-ion context is also discussed.
↳ hep-phhep-exnucl-exnucl-thPRD(2019)·3 citations
14
Viscosity spectral functions of resonating fermions in the quantum virial expansion
Yusuke Nishida
We consider two-component fermions with a zero-range interaction both in two and three dimensions and study their spectral functions of bulk and shear viscosities for an arbitrary scattering length. Here the Kubo formulas are systematically evaluated up to the second order in the quantum virial expansion applicable to the high-temperature regime. In particular, our computation of the bulk viscosity spectral function is facilitated by expressing it with the contact-contact response function, which can be measured experimentally under the periodic modulation of the scattering length. The obtained formulas are fully consistent with the known constraints on high-frequency tail and sum rule. Although our static shear viscosity agrees with that derived from the kinetic theory, our static bulk viscosity disagrees. Furthermore, the latter for three dimensions exhibits an unexpected non-analyticity of $ζ \sim (ln a^{2}) / a^{2}$ in the unitarity limit $a \to \infty$ , which thus challenges the "crossover" hypothesis.
↳ cond-mat.quant-gascond-mat.stat-mechnucl-thAnnals Phys.(2019)·33 citations

Affiliations

first authorsco-authorsvia INSPIRE

Short Range Operator Contributions to 0νββ decay from LQCD

Neutron skins of atomic nuclei: per aspera ad astra

Testing the tetraquark mixing framework from QCD sum rules for a0​(980)

Pion generalized parton distribution from lattice QCD

Role of the Symmetry Energy on the Structure of Neutron Stars with Unified Equations of State

A background estimator for jet studies in p+p and A+A collisions

Viscosity spectral functions of resonating fermions in the quantum virial expansion

Affiliations

Short Range Operator Contributions to $0 ν β β$ decay from LQCD

Testing the tetraquark mixing framework from QCD sum rules for $a_{0} (980)$