Nuclear Theory·nucl-th

Monday·October 31, 2016

10 papers—8 primary·2 cross-listed

01
Reconciling threshold and subthreshold expansions for pion-nucleon scattering
D. Siemens🇩🇪 · J. Ruiz de Elvira🇨🇭 · E. Epelbaum🇺🇸 · M. Hoferichter🇺🇸 · H. Krebs🇺🇸 · B. Kubis🇩🇪 · U.-G. Meißner🇩🇪
Heavy-baryon chiral perturbation theory (ChPT) at one loop fails in relating the pion-nucleon amplitude in the physical region and for subthreshold kinematics due to loop effects enhanced by large low-energy constants. Studying the chiral convergence of threshold and subthreshold parameters up to fourth order in the small-scale expansion, we address the question to what extent this tension can be mitigated by including the $Δ (1232)$ as an explicit degree of freedom and/or using a covariant formulation of baryon ChPT. We find that the inclusion of the $Δ$ indeed reduces the low-energy constants to more natural values and thereby improves consistency between threshold and subthreshold kinematics. In addition, even in the $Δ$ -less theory the resummation of $1/ m_{N}$ corrections in the covariant scheme improves the results markedly over the heavy-baryon formulation, in line with previous observations in the single-baryon sector of ChPT that so far have evaded a profound theoretical explanation.
nucl-thhep-phPLB(2017)·124 citations
02
Universal dimer-dimer scattering in lattice effective field theory
Serdar Elhatisari🇹🇷 · Kris Katterjohn🇺🇸 · Dean Lee🇺🇸 · Ulf-G. Meißner🇩🇪 · Gautam Rupak🇺🇸
We consider two-component fermions with short-range interactions and large scattering length. This system has universal properties that are realized in several different fields of physics. In the limit of large fermion-fermion scattering length $a_{ff}$ and zero-range interaction, all properties of the system scale proportionally with $a_{ff}$ . For the case with shallow bound dimers, we calculate the dimer-dimer scattering phase shifts using lattice effective field theory. We extract the universal dimer-dimer scattering length $a_{dd} / a_{ff} = 0.618 (30)$ and effective range $r_{dd} / a_{ff} = - 0.431 (48)$ . This result for the effective range is the first calculation with quantified and controlled systematic errors. We also benchmark our methods by computing the fermion-dimer scattering parameters and testing some predictions of conformal scaling of irrelevant operators near the unitarity limit.
nucl-thcond-mat.quant-gashep-latphysics.atom-phPLB(2017)·18 citations
03
Calculation of the astrophysical S-factor S_12 with the Lorentz integral transform
Sergio Deflorian · Victor D. Efros · Winfried Leidemann
The LIT approach is tested for the calculation of astrophysical S-factors. As an example the S-factor of the reaction 2H(p,gamma)3He is considered. It is discussed that a sufficiently high density of LIT states at low energies is necessary for a precise determination of S-factors. In particular it is shown that the hyperspherical basis is not very well suited for such a calculation and that a different basis system is much more advantageous. A comparison of LIT results with calculations, where continuum wave functions are explicitly used, shows that the LIT approach leads to reliable results. It is also shown how an error estimate of the LIT inversion can be obtained.
nucl-thFew Body Syst.(2017)·4 citations
04
Benchmark calculation of p-3H and n-3He scattering
M. Viviani🇮🇹 · A. Deltuva🇱🇹 · R. Lazauskas🇫🇷 · A.C. Fonseca🇵🇹 · A. Kievsky🇮🇹 · L.E. Marcucci🇮🇹
p-3H and n-3He scattering in the energy range above the n-3He but below the d-d thresholds is studied by solving the 4-nucleon problem with a realistic nucleon-nucleon interaction. Three different methods -- Alt, Grassberger and Sandhas, Hyperspherical Harmonics, and Faddeev-Yakubovsky -- have been employed and their results for both elastic and charge-exchange processes are compared. We observe a good agreement between the three different methods, thus the obtained results may serve as a benchmark. A comparison with the available experimental data is also reported and discussed.
nucl-thnucl-exPRC(2017)·33 citations
05
Inconsistency of the interactions between pseudoscalar, spinor and Rarita-Schwinger fields
D. Badagnani · A. Mariano · C. Barbero
We perform the Dirac quantization of RS fields interacting with a spinor and the first derivative of a pseudoscalar field. We achieve the calculations for two forms of this interaction: first we review the conventional coupling of lowest derivative order, reproducing the well known inconsistencies in its anticommutator algebra. Then, we perform the analysis on the next order term popularly known as spin 3/2 gauge invariant interaction, which is claimed to be free of these inconsistencies. Nevertheless we find that the direct application of the Dirac formalism leads to inconsistencies in complete analogy to the previous case. This is of high relevance in the particle phenomenology field, where these interactions are used to interpret experimental data involving Delta(1232) resonances.
nucl-thhep-ph0 citations
06
The microscopic structure of $π N N$ , $π N Δ$ and $π ΔΔ$ vertices in a hybrid constituent quark model
Ju-Hyun Jung🇦🇹 · Wolfgang Schweiger🇦🇹
We present a microscopic description of the strong $π N N$ , $π N Δ$ and $π ΔΔ$ vertices. Our starting point is a constituent-quark model supplemented by an additional $3 q π$ non-valence component. In the spirit of chiral constituent-quark models, quarks are allowed to emit and reabsorb a pion. This multichannel system is treated in a relativistically invariant way within the framework of point-form quantum mechanics. Starting with a common $S U (6)$ spin-flavor-symmetric wave function for $N$ and $Δ$ , we calculate the strength of the $π N N$ , $π N Δ$ and $π ΔΔ$ couplings and the corresponding vertex form factors. Our results are in accordance with phenomenological fits of these quantities that have been obtained within purely hadronic multichannel models for baryon resonances.
nucl-thBled Workshops Phys.(2016)·0 citations
07
Testing the hadronic spectrum in the strange sector
Paolo Parotto🇺🇸
Heavier resonances are continually being added to the hadronic spectrum from the Particle Data Group that follow an exponentially increasing mass spectrum. However, it has been suggested that even further states predicted from Quark Models are needed in the hadronic spectrum in order to improve the agreement between the hadron resonance gas model predictions and lattice QCD data. We find that the inclusion of such states with extrapolated branching ratios slightly decreases the freezeout temperature. To eliminate ambiguities, we introduce a first principle method to extract the freeze-out temperature for charged kaons from experimental data, which yields a lower bound of $T_{fo} ≳$ 145 MeV for the highest collision energy at RHIC.
nucl-thhep-lathep-phJ.Phys.Conf.Ser.(2017)·0 citations
08
Jet structure modifications in heavy-ion collisions with JEWEL
Raghav Kunnawalkam Elayavalli🇺🇸
Key features of jet-medium interactions in heavy-ion collisions are modifications to the jet structure. Recent results from experiments at the LHC and RHIC have motivated several theoretical calculations and monte carlo models towards predicting these observables simultaneously. In this report, the recoil picture in \textsc{Jewel} is summarized and two independent procedures through which background subtraction can be performed in \textsc{Jewel} are introduced. Information of the medium recoil in \textsc{Jewel} significantly improves its description of several jet shape measurements.
nucl-thhep-phJ.Phys.Conf.Ser.(2017)·4 citations
09
Unexpected properties of interactions of high energy protons
I.M. Dremin🇷🇺
Experimental data on proton-proton interactions in high energy collisions show quite a special and unexpected behaviour of the proportion of elastic scattering compared to inelastic processes with increasing energy. It decreases at the beginning (at comparatively low energies) but then starts increasing. From Intersecting Storage Rings (ISR) energies of 23.5 - 62.5 GeV up to higher energies 7 - 13 TeV at the Large Hadron Collider (LHC) it increases by a factor more than 1.5! According to intuitive classical ideas we would expect a stable tendency with increasing proportion of the break-down of protons compared to their survival probability. One can assume that either the asymptotic freedom or the extremely short time of flight of high energy protons through each other are in charge of such a surprising effect. The unquestionable principle of unitarity combined with the available experimental data on elastic scattering is used to get new conclusions about the shape of the interaction region of colliding protons. Its evolution at present energies is considered. Some predictions about its behaviour at even higher energies are described with different assumptions on relative roles of elastic scattering and inelastic processes. The shape can transform rather drastically if the proportion of elastic processes keeps rising. This unexpected property leads to an unexpected corollary. The possible origin of the effect and its interrelation to the strong interaction dynamics are speculated.
↳ hep-phhep-exnucl-exnucl-thPhys.Usp.(2017)·22 citations
10
Coupling constant corrections in a holographic model of heavy ion collisions
Sašo Grozdanov🇳🇱 · Wilke van der Schee🇺🇸
We initiate a holographic study of coupling-dependent heavy ion collisions by analysing for the first time the effects of leading-order, inverse coupling constant corrections. In the dual description, this amounts to colliding gravitational shock waves in a theory with curvature-squared terms. We find that at intermediate coupling, nuclei experience less stopping and have more energy deposited near the lightcone. When the decreased coupling results in an 80% larger shear viscosity, the time at which hydrodynamics becomes a good description of the plasma created from high energy collisions increases by 25%. The hydrodynamic phase of the evolution starts with a wider rapidity profile and smaller entropy.
↳ hep-thgr-qchep-phnucl-thPRL(2017)·61 citations

Affiliations

first authorsco-authorsvia INSPIRE