Nuclear Theory·nucl-th

Tuesday·June 20, 2017

17 papers—11 primary·6 cross-listed

12
Towards an effective field theory approach to the neutrinoless double-beta decay
Mihai Horoi🇺🇸 · Andrei Neacsu🇺🇸
Weak interaction in nuclei represents a well-known venue for testing many of the fundamental symmetries of the Standard Model. In particular, neutrinoless double-beta decay offers the possibility to test Beyond Standard Model theories predicting that neutrinos are Majorana fermions and the lepton number conservation is violated. This paper focuses on an effective field theory approach to neutrinoless double-beta decay for extracting information regarding the properties of the Beyond Standard Model Lagrangian responsible for this process. We use shell model nuclear matrix elements and the latest experimental lower limits for the half-lives to extract the lepton number violating parameters of five nuclei of experimental interest, and lower limits for the energy scales of the new physics.
↳ hep-phnucl-th38 citations
13
Photo- and electroproduction of $Λ (1405)$ via $γ^{(*)} p \to K^{+} π^{+} Σ^{-}$
Seung-il Nam🇰🇷
In this work, we perform a \textit{toy-model} analysis for the unpolarized photo- and electroproduction of $Λ (1405) \equiv Λ^{*}$ via $γ^{(*)} p \to K^{+} π^{+} Σ^{-}$ by employing the effective Lagrangian approach at the tree level only. We consider that $Λ^{*}$ consists of the high-mass ( $H$ ) and low-mass ( $L$ ) poles as suggested by the chiral unitary model (ChUM). We determine all the model parameters including coupling constants and cutoff parameters for the phenomenological strong form factors by using the theoretical information from ChUM and available experimental data. The electromagnetic (EM) form factors for the two poles are parameterized appropriately being similar to that for the neutron by employing the ChUM estimates for the EM root-mean-squared (rms) radii for the two poles. We observe from the numerical calculations that, for the photoproduction of $Λ^{*}$ , the interference between the two poles turns out to be destructive, resulting in the single-peak line at $M_{π^{+} Σ^{-}} \approx 1405$ MeV in the invariant-mass distribution. On the contrary, there appear two peaks in the distribution for the electroproduction as observed in the CLAS/Jlab electroproduction data, due to the constructive interference, which is mainly caused by the Dirac form factors for the two poles. From this observation, we conclude that, in order to explain the photo- and electroproduction data simultaneously, i.e., \textit{single} and \textit{double} peaks, respectively, in the invariant-mass distribution, the interference patterns for the two poles should follow those suggested by ChUM. In turn, it is a strong theoretical and experimental supports for the two-pole structure scenario for $Λ^{*}$ .
↳ hep-phnucl-thPRD(2017)·9 citations
14
Analytic parametrizations of the $γ^{*} N \to N (1440)$ form factors inspired by Light-Front holography
G. Ramalho🇧🇷
We present analytic parametrizations for the $γ^{*} N \to N (1440)$ form factors derived from light-front holography in leading twist approximation. The new parametrizations describe the electromagnetic form factors using analytic functions dependent on the masses of the $ρ$ meson and respective radial excitations, as well as the masses of the nucleon and the resonance $N (1440)$ . The free parameters of the model, associated with three independent couplings, are interpreted as bare couplings, and are fixed by the nucleon data for large $Q^{2}$ . The proposed parametrizations compare remarkably well with the empirical data for $Q^{2} > 2$ GeV $^{2}$ , corroborating the dominant role of the valence quark degrees of freedom in the $γ^{*} N \to N (1440)$ transition.
↳ hep-phhep-exnucl-exnucl-thPRD(2017)·19 citations
15
Violation of Positivity Bounds in Models of Generalized Parton Distributions
Brian C. Tiburzi🇺🇸 · Gaurav Verma🇺🇸
As with parton distributions, flexible phenomenological parameterizations of generalized parton distributions (GPDs) are essential for their extraction from data. The large number of constraints imposed on GPDs make simple Lorentz covariant models viable; but, such models are often incomplete in that they employ the impulse approximation. Using the GPD of the pion as a test case, we show that the impulse approximation can lead to violation of the positivity bound required of GPDs. We focus on a particular model of the pion bound-state vertex that was recently proposed and demonstrate that satisfying the bound is not guaranteed by Lorentz covariance. Violation of the positivity bound is tied to a problematic mismatch between the behavior of the quark distribution at the endpoint and the crossover value of the GPD.
↳ hep-phnucl-thPRD(2017)·3 citations
16
On the hadron mass decomposition
Cédric Lorcé (Ecole polytechnique, CPHT)🇫🇷
We argue that the standard decompositions of the hadron mass overlook pressure effects, and hence should be interpreted with great care. Based on the semiclassical picture, we propose a new decomposition that properly accounts for these pressure effects. Because of Lorentz covariance, we stress that the hadron mass decomposition automatically comes along with a stability constraint, which we discuss for the first time. We show also that if a hadron is seen as made of quarks and gluons, one cannot decompose its mass into more than two contributions without running into trouble with the consistency of the physical interpretation. In particular, the so-called quark mass and trace anomaly contributions appear to be purely conventional. Based on the current phenomenological values, we find that in average quarks exert a repulsive force inside nucleons, balanced exactly by the gluon attractive force.
↳ hep-phhep-latnucl-thEPJC(2018)·138 citations
17
Radiative energy loss of neighboring subjets
Yacine Mehtar-Tani🇺🇸 · Konrad Tywoniuk🇨🇭
We compute the in-medium energy loss probability distribution of two neighboring subjets at leading order, in the large- $N_{c}$ approximation. Our result exhibits a gradual onset of color decoherence of the system and accounts for two expected limiting cases. When the angular separation is smaller than the characteristic angle for medium-induced radiation, the two-pronged substructure lose energy coherently as a single color charge, namely that of the parent parton. At large angular separation the two subjets lose energy independently. Our result is a first step towards quantifying effects of energy loss as a result of the fluctuation of the multi-parton jet substructure and therefore goes beyond the standard approach to jet quenching based on single parton energy loss. We briefly discuss applications to jet observables in heavy-ion collisions.
↳ hep-phnucl-thNPA(2018)·55 citations

Affiliations

first authorsco-authorsvia INSPIRE

Towards an effective field theory approach to the neutrinoless double-beta decay

Photo- and electroproduction of Λ(1405) via γ(∗)p→K+π+Σ−

Analytic parametrizations of the γ∗N→N(1440) form factors inspired by Light-Front holography

Violation of Positivity Bounds in Models of Generalized Parton Distributions

On the hadron mass decomposition

Radiative energy loss of neighboring subjets

Affiliations

Photo- and electroproduction of $Λ (1405)$ via $γ^{(*)} p \to K^{+} π^{+} Σ^{-}$

Analytic parametrizations of the $γ^{*} N \to N (1440)$ form factors inspired by Light-Front holography