Nuclear Theory·nucl-th

Friday·February 12, 2021

12 papers—4 primary·8 cross-listed

05
Comment on " $σ$ -meson: Four-quark versus two-quark components and decay width in a Bethe-Salpeter approach"
B. Blankleider🇦🇺 · A. N. Kvinikhidze🇬🇪
In a recent paper by N. Santowsky et al. [Phys. Rev. D 102, 056014 (2020)], covariant coupled equations were derived to describe a tetraquark in terms of a mix of four-quark states $2 q 2 q ˉ$ and two-quark states $q q ˉ$ . These equations were expressed in terms of vertices describing the disintegration of a tetraquark into identical two-meson states, into a diquark-antidiquark pair, and into a quark-antiquark pair. We show that these equations are inconsistent as they imply a $q q ˉ$ Bethe-Salpeter kernel that is $q q ˉ$ -reducible.
↳ hep-phnucl-th2 citations
06
Spectrum of the doubly charmed molecular pentaquarks in chiral effective field theory
Kan Chen🇨🇳 · Bo Wang🇨🇳 · Shi-Lin Zhu🇨🇳
We perform a systematic study on the interactions of the $Σ_{c}^{(*)} D^{(*)}$ systems within the framework of chiral effective field theory. We introduce the contact term, one-pion-exchange and two-pion-exchange contributions to describe the short-, long-, and intermediate-range interactions. The low energy constants of the $Σ_{c}^{(*)} D^{(*)}$ systems are estimated from the $N N ˉ$ scattering data by introducing a quark level Lagrangian. With three solutions of LECs, all the $Σ_{c}^{(*)} D^{(*)}$ systems with isospin $I = 1/2$ can form bound states, in which different inputs of LECs may lead to distinguishable mass spectra. In addition, we also investigate the interactions of the charmed-bottom $Σ_{c}^{(*)} B ˉ^{(*)}$ , $Σ_{b}^{(*)} D^{(*)}$ , and $Σ_{b}^{(*)} B ˉ^{(*)}$ systems. Among the obtained bound states, the bindings become deeper when the reduced masses of the corresponding systems are heavier.
↳ hep-phhep-exhep-latnucl-thPRD(2021)·31 citations
07
Pairing and the spin susceptibility of the polarized unitary Fermi gas in the normal phase
Lukas Rammelmüller🇩🇪 · Yaqi Hou🇺🇸 · Joaquín E. Drut🇺🇸 · Jens Braun🇩🇪
We theoretically study the pairing behavior of the unitary Fermi gas in the normal phase. Our analysis is based on the static spin susceptibility, which characterizes the response to an external magnetic field. We obtain this quantity by means of the complex Langevin approach and compare our calculations to available literature data in the spin-balanced case. Furthermore, we present results for polarized systems, where we complement and expand our analysis at high temperature with high-order virial expansion results. The implications of our findings for the phase diagram of the spin-polarized unitary Fermi gas are discussed, in the context of the state of the art.
↳ cond-mat.quant-gashep-latnucl-thPRA(2021)·16 citations
08
Effective field theory for dilute Fermi systems at fourth order
C. Wellenhofer🇩🇪 · C. Drischler🇺🇸 · A. Schwenk🇩🇪
We discuss high-order calculations in perturbative effective field theory for fermions at low energy scales. The Fermi-momentum or $k_{F} a_{s}$ expansion for the ground-state energy of the dilute Fermi gas is calculated to fourth order, both in cutoff regularization and in dimensional regularization. For the case of spin one-half fermions we find from a Bayesian analysis that the expansion is well-converged at this order for $∣ k_{F} a_{s} ∣ ≲ 0.5$ . Further, we show that Padé-Borel resummations can improve the convergence for $∣ k_{F} a_{s} ∣ ≲ 1$ . Our results provide important constraints for nonperturbative calculations of ultracold atoms and dilute neutron matter.
↳ cond-mat.quant-gashep-phnucl-thPRC(2021)·12 citations
09
Pion form factor and charge radius from Lattice QCD at physical point
Xiang Gao🇺🇸 · Nikhil Karthik🇺🇸 · Swagato Mukherjee🇺🇸 · Peter Petreczky🇺🇸 · Sergey Syritsyn🇺🇸 · Yong Zhao🇺🇸
We present our results on the electromagnetic form factor of pion over a wide range of $Q^{2}$ using lattice QCD simulations with Wilson-clover valence quarks and HISQ sea quarks. We study the form factor at the physical point with a lattice spacing $a = 0.076$ fm. To study the lattice spacing and quark mass effects, we also present results for 300 MeV pion at two different lattice spacings $a = 0.04$ and 0.06 fm. The lattice calculations at the physical quark mass appear to agree with the experimental results. Through fits to the form factor, we estimate the charge radius of pion for physical pion mass to be $⟨ r_{π}^{2} ⟩ = 0.42 (2) fm^{2}$ .
↳ hep-lathep-exhep-phnucl-thPRD(2021)·60 citations
10
New insights into nuclear physics and weak mixing angle using electroweak probes
M. Cadeddu🇮🇹 · N. Cargioli🇮🇹 · F. Dordei🇮🇹 · C. Giunti🇮🇹 · Y.F. Li🇨🇳 · E. Picciau🇮🇹 · C.A. Ternes🇮🇹 · Y.Y. Zhang🇨🇳
Using the new results on coherent elastic neutrino-nucleus scattering data in cesium-iodide provided by the COHERENT experiment, we determine a new measurement of the average neutron rms radius of $^{133} Cs$ and $^{127} I$ . In combination with the atomic parity violation (APV) experimental result, we derive the most precise measurement of the neutron rms radii of $^{133} Cs$ and $^{127} I$ , disentangling for the first time the contributions of the two nuclei. By exploiting these measurements we determine the corresponding neutron skin values for $^{133} Cs$ and $^{127} I$ . These results suggest a preference for models which predict large neutron skin values, as corroborated by the only other electroweak measurements of the neutron skin of $^{208} Pb$ performed by PREX experiments. Moreover, for the first time, we obtain a data-driven APV+COHERENT measurement of the low-energy weak mixing angle with a percent uncertainty, independent of the value of the average neutron rms radius of $^{133} Cs$ and $^{127} I$ , that is allowed to vary freely in the fit. The value of the low-energy weak mixing angle that we found is slightly larger than the standard model prediction.
↳ hep-phnucl-thPRC(2021)·49 citations
11
First analysis of world polarized DIS data with small- $x$ helicity evolution
Daniel Adamiak🇺🇸 · Yuri V. Kovchegov🇺🇸 · W. Melnitchouk🇺🇸 · Daniel Pitonyak🇺🇸 · Nobuo Sato🇺🇸 · Matthew D. Sievert🇺🇸
We present a Monte Carlo based analysis of the combined world data on polarized lepton-nucleon deep-inelastic scattering at small Bjorken $x$ within the polarized quark dipole formalism. We show for the first time that double-spin asymmetries at $x < 0.1$ can be successfully described using only small- $x$ evolution derived from first-principles QCD, allowing predictions to be made for the $g_{1}$ structure function at much smaller $x$ . Anticipating future data from the Electron-Ion Collider, we assess the impact of electromagnetic and parity-violating polarization asymmetries on $g_{1}$ and demonstrate an extraction of the individual flavor helicity PDFs at small $x$ .
↳ hep-phhep-exnucl-exnucl-thPRD(2021)·61 citations
12
Charged Lepton Flavor Violation at the EIC
Vincenzo Cirigliano🇺🇸 · Kaori Fuyuto🇺🇸 · Christopher Lee🇺🇸 · Emanuele Mereghetti🇺🇸 · Bin Yan🇺🇸
We present a comprehensive analysis of the potential sensitivity of the Electron-Ion Collider (EIC) to charged lepton flavor violation (CLFV) in the channel $e p \to τ X$ , within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). We compute the relevant cross sections to leading order in QCD and electroweak corrections and perform simulations of signal and SM background events in various $τ$ decay channels, suggesting simple cuts to enhance the associated estimated efficiencies. To assess the discovery potential of the EIC in $τ$ - $e$ transitions, we study the sensitivity of other probes of this physics across a broad range of energy scales, from $pp \to e τ X$ at the Large Hadron Collider to decays of $B$ mesons and $τ$ leptons, such as $τ \to e γ$ , $τ \to e ℓ^{+} ℓ^{-}$ , and crucially the hadronic modes $τ \to e Y$ with $Y \in {π, K, π π, K π, ...}$ . We find that electroweak dipole and four-fermion semi-leptonic operators involving light quarks are already strongly constrained by $τ$ decays, while operators involving the $c$ and $b$ quarks present more promising discovery potential for the EIC. An analysis of three models of leptoquarks confirms the expectations based on the SMEFT results. We also identify future directions needed to maximize the reach of the EIC in CLFV searches: these include an optimization of the $τ$ tagger in hadronic channels, an exploration of background suppression through tagging $b$ and $c$ jets in the final state, and a global fit by turning on all SMEFT couplings, which will likely reveal new discovery windows for the EIC.
↳ hep-phhep-exnucl-exnucl-thJHEP(2021)·90 citations

Affiliations

first authorsco-authorsvia INSPIRE