Nuclear Theory·nucl-th

Monday·September 9, 2019

9 papers—2 primary·7 cross-listed

03
Patterns of flavour symmetry breaking in hadron matrix elements involving u, d and s quarks
J.M. Bickerton🇦🇺 · R. Horsley🇬🇧 · Y. Nakamura🇯🇵 · H. Perlt🇩🇪 · D. Pleiter🇩🇪 · P.E.L. Rakow🇬🇧 · G. Schierholz🇩🇪 · H. Stüben🇩🇪 · R.D. Young🇦🇺 · J.M. Zanotti🇦🇺
By considering a flavour expansion about the SU(3)-flavour symmetric point, we investigate how flavour-blindness constrains octet baryon matrix elements after SU(3) is broken by the mass difference between quarks. Similarly to hadron masses we find the expansions to be constrained along a mass trajectory where the singlet quark mass is held constant, which provides invaluable insight into the mechanism of flavour symmetry breaking and proves beneficial for extrapolations to the physical point. Expansions are given up to third order in the expansion parameters. Considering higher orders would give no further constraints on the expansion parameters. The relation of the expansion coefficients to the quark-line-connected and quark-line disconnected terms in the 3-point correlation functions is also given. As we consider Wilson clover-like fermions, the addition of improvement coefficients is also discussed and shown to be included in the formalism developed here. As an example of the method we investigate this numerically via a lattice calculation of the flavour-conserving matrix elements of the vector first class form factors.
↳ hep-lathep-phnucl-thPRD(2019)·16 citations
04
Coupled $K^{+} Λ$ and $K^{0} Λ$ photoproduction off the nucleon: Consequences from the recent CLAS and MAMI data and the $N (1680) P_{11}$ narrow state
T. Mart🇮🇩
The new $γ n \to K^{0} Λ$ data obtained from the CLAS and MAMI collaborations are analyzed by employing an effective Lagrangian method. The constructed model can describe all available experimental data in both $γ p \to K^{+} Λ$ and $γ n \to K^{0} Λ$ channels, simultaneously. The background part of the model is built from the appropriate intermediate states involving the nucleon, kaon, and hyperon exchanges, whereas the resonance part is constructed from the consistent interaction Lagrangians and propagators. To check the performance of the model a detailed comparison between the calculated observables and experimental data in both isospin channels is presented, from which a nice agreement can be observed. The discrepancy between the CLAS and MAMI data in the $γ n \to K^{0} Λ$ channel is analyzed by utilizing three different models; M1, M2, and M3 that fit the CLAS, MAMI, and both CLAS and MAMI data sets, respectively. The effect of this discrepancy is studied by investigating the significance of individual nucleon resonances and the predicted beam-target helicity asymmetry $E$ that has been measured by the CLAS collaboration recently. It is found that the $N (1720) P_{13}$ , $N (1900) P_{13}$ , and $N (2060) D_{15}$ resonances are significant for improving the agreement between model calculation and data. This result is relatively stable to the choice of the model. The helicity asymmetry $E$ can be better explained by the models M1 and M3. Finally, the effect of the $N (1680) P_{11}$ narrow resonance on the cross section of both isospin channels is explored. It is found that the effect is more sensitive in the $γ n \to K^{0} Λ$ channel. In this case the model M3, that fits both CLAS and MAMI data, yields a more realistic effect.
↳ hep-phnucl-thPRD(2019)·20 citations
05
Vacuum energy in the effective field theory of general relativity II: Inclusion of fermions and a comment on the QCD contribution
J. Gegelia🇩🇪 · Ulf-G. Meißner🇬🇪
Recently in the framework of a two-loop order calculation for an effective field theory of scalar and vector fields interacting with the metric field we have shown that for the cosmological constant term which is fixed by the condition of vanishing vacuum energy the graviton remains massless and there exists a self-consistent effective field theory of general relativity defined on a flat Minkowski background. In the current paper we extend the two-loop analysis for an effective field theory of fermions interacting with the gravitational field and obtain an analogous result. We also address the issues of fine tuning of the strong interaction contribution to the vacuum energy and the compatibility of chiral symmetry in the light quark sector with the consistency of the effective field theory of general relativity in a flat Minkowski background.
↳ hep-thgr-qchep-phnucl-thPRD(2019)·3 citations
06
Study of QCD dynamics using small systems
Suman Deb🇮🇳 · Golam Sarwar🇮🇳 · Raghunath Sahoo🇮🇳 · Jan-e Alam🇮🇳
The multiplicity, finite system size and collision energy dependencies of heat capacity ( $C_{V}$ ), conformal symmetry breaking measure (CSBM) and speed of sound ( $c_{s}$ ) have been investigated using ALICE data for $p + p$ collisions at $s$ = 7 TeV. The aim of this study is to ascertain the possibility of formation of a thermalized medium in such collisions. We find that there is a threshold in charged particle multiplicity beyond which $C_{V}$ , CSBM and $c_{s}$ attain plateau. The presence of such threshold in multiplicity is further reflected in the variation of these quantities with center-of-mass energy ( $s_{N N}$ ). In order to have a grasp on experimentally obtained results, variation of $⟨ p_{T} ⟩$ with multiplicity has also been studied. The experimental results have been contrasted with PYTHIA8 and it is found that PYTHIA8 is inadequate to explain the features reflected in these quantities, thereby indicating the possibility of thermalization in such small system. It is also observed that the finite size effects alone cannot explain the non-extensive nature of particle spectra in $p + p$ collisions.
↳ hep-phnucl-exnucl-thEPJA(2021)·16 citations
07
Collinear Factorization in Wide-Angle Hadron Pair Production in $e^{+} e^{-}$ Annihilation
E. Moffat🇺🇸 · T. C. Rogers🇺🇸 · N. Sato🇺🇸 · A. Signori🇺🇸
We compute the inclusive unpolarized dihadron production cross section in the far from back-to-back region of $e^{+} e^{-}$ annihilation in leading order pQCD using existing fragmentation function fits and standard collinear factorization, focusing on the large transverse momentum region where transverse momentum is comparable to the hard scale (the center-of-mass energy). We compare with standard transverse-momentum-dependent (TMD) fragmentation function-based predictions intended for the small transverse momentum region with the aim of testing the expectation that the two types of calculation roughly coincide at intermediate transverse momentum. We find significant tension, within the intermediate transverse momentum region, between calculations done with existing non-perturbative TMD fragmentation functions and collinear factorization calculations if the center-of-mass energy is not extremely large. We argue that $e^{+} e^{-}$ measurements are ideal for resolving this tension and exploring the large-to-small transverse momentum transition, given the typically larger hard scales ( $≳ 10$ GeV) of the process as compared with similar scenarios that arise in semi-inclusive deep inelastic scattering and fixed-target Drell-Yan measurements.
↳ hep-phnucl-thPRD(2019)·16 citations
08
$I = 3$ three-pion scattering amplitude from lattice QCD
Tyler D. Blanton🇺🇸 · Fernando Romero-López🇪🇸 · Stephen R. Sharpe🇺🇸
We analyze the spectrum of two- and three-pion states of maximal isospin obtained recently for isosymmetric QCD with pion mass $M \approx 200$ MeV in Ref. [1]. Using the relativistic three-particle quantization condition, we find $\sim 2 σ$ evidence for a nonzero value for the contact part of the three- $π^{+}$ ( $I = 3$ ) scattering amplitude. We also compare our results to leading-order chiral perturbation theory. We find good agreement at threshold, and some tension in the energy dependent part of the three- $π^{+}$ scattering amplitude. We also find that the two- $π^{+}$ ( $I = 2$ ) spectrum is fit well by an $s$ -wave phase shift that incorporates the expected Adler zero.
↳ hep-lathep-exhep-phnucl-thPRL(2020)·126 citations
09
Nakanishi integral representation for the quark-photon vertex
Vladimir Sauli🇨🇿
Using a nonperturbative framework of Dyson-Schwinger equations a class of Nakanishi's like integral representations for the transverse part of the quark-photon vertex is derived. For this but also for its own purpose the two and single variable integral representations for untruncated quark-antiquark-photon vertex is proposed as well. To exhibit the adequacy of proposed representation, the Dyson-Schwinger equation for the vertex is transformed into the equivalent set of coupled integro-differential equations for Nakanishi weight functions: functions that appear linearly in the numerator of given integral representation. Their knowledge then provide self-consistent nonperturbative solution for the vertex in the entire Minkowski space.
↳ hep-phnucl-th2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Patterns of flavour symmetry breaking in hadron matrix elements involving u, d and s quarks

Coupled K+Λ and K0Λ photoproduction off the nucleon: Consequences from the recent CLAS and MAMI data and the N(1680)P11​ narrow state

Vacuum energy in the effective field theory of general relativity II: Inclusion of fermions and a comment on the QCD contribution

Study of QCD dynamics using small systems

Collinear Factorization in Wide-Angle Hadron Pair Production in e+e− Annihilation

I=3 three-pion scattering amplitude from lattice QCD

Nakanishi integral representation for the quark-photon vertex

Affiliations

Coupled $K^{+} Λ$ and $K^{0} Λ$ photoproduction off the nucleon: Consequences from the recent CLAS and MAMI data and the $N (1680) P_{11}$ narrow state

Collinear Factorization in Wide-Angle Hadron Pair Production in $e^{+} e^{-}$ Annihilation

$I = 3$ three-pion scattering amplitude from lattice QCD