Nuclear Theory·nucl-th

Friday·February 13, 2015

13 papers—5 primary·8 cross-listed

06
Interplay of relativistic and nonrelativistic transport in atomically precise segmented graphene nanoribbons
Constantine Yannouleas🇺🇸 · Igor Romanovsky🇺🇸 · Uzi Landman🇺🇸
Graphene's isolation launched explorations of fundamental relativistic physics originating from the planar honeycomb lattice arrangement of the carbon atoms, and of potential technological applications in nanoscale electronics. Bottom-up fabricated atomically-precise segmented graphene nanoribbons, SGNRs, open avenues for studies of electrical transport, coherence, and interference effects in metallic, semiconducting, and mixed GNRs, with different edge terminations. Conceptual and practical understanding of electric transport through SGNRs is gained through nonequilibrium Green's function (NEGF) conductance calculations and a Dirac continuum model that absorbs the valence-to-conductance energy gaps as position-dependent masses, including topological-in-origin mass-barriers at the contacts between segments. The continuum model reproduces the NEGF results, including optical Dirac Fabry-Perot (FP) equidistant oscillations for massless relativistic carriers in metallic armchair SGNRs, and an unequally-spaced FP pattern for mixed armchair-zigzag SGNRs where carriers transit from a relativistic (armchair) to a nonrelativistic (zigzag) regime. This provides a unifying framework for analysis of coherent transport phenomena and interpretation of forthcoming experiments in SGNRs.
↳ cond-mat.mes-hallcond-mat.mtrl-scihep-phnucl-thSci.Rep.(2015)·1 citation
07
Flavor dependence of baryon melting temperature in effective models of QCD
Juan M. Torres-Rincon🇫🇷 · Benjamin Sintes🇫🇷 · Joerg Aichelin🇫🇷
We apply the three-flavor (Polyakov-)Nambu-Jona-Lasinio model to generate baryons as quark-diquark bound states using many-body techniques at finite temperature. All the baryonic states belonging to the octet and decuplet flavor representations are generated in the isospin-symmetric case. For each state we extract the melting temperature at which the baryon may decay into a quark-diquark pair. We seek for an evidence of the strangeness dependence of the baryon melting temperature as suggested by the statistical thermal models and supported by lattice-QCD results. A clear and robust signal for this claim is found, pointing to a flavor dependence of the hadronic deconfinement temperature.
↳ hep-phnucl-thPRC(2015)·34 citations
08
Assessment of molecular effects on neutrino mass measurements from tritium beta decay
L.I. Bodine🇺🇸 · D.S. Parno🇺🇸 · R.G.H. Robertson🇺🇸
The beta decay of molecular tritium currently provides the highest sensitivity in laboratory-based neutrino mass measurements. The upcoming Karlsruhe Tritium Neutrino (KATRIN) experiment will improve the sensitivity to 0.2 eV, making a percent-level quantitative understanding of molecular effects essential. The modern theoretical calculations available for neutrino-mass experiments agree with spectroscopic data. Moreover, when neutrino-mass experiments performed in the 1980s with gaseous tritium are re-evaluated using these modern calculations, the extracted neutrino mass-squared values are consistent with zero instead of being significantly negative. On the other hand, the calculated molecular final-state branching ratios are in tension with dissociation experiments performed in the 1950s. We re-examine the theory of the final-state spectrum of molecular tritium decay and its effect on the determination of the neutrino mass, with an emphasis on the role of the vibrational- and rotational-state distribution in the ground electronic state. General features can be reproduced quantitatively from considerations of kinematics and zero-point motion. We summarize the status of validation efforts and suggest means for resolving the apparent discrepancy in dissociation rates.
↳ nucl-exhep-phnucl-thPRC(2015)·76 citations
09
Nucleons and parity doubling across the deconfinement transition
Gert Aarts🇬🇧 · Chris Allton🇬🇧 · Simon Hands🇬🇧 · Benjamin Jäger🇬🇧 · Chrisanthi Praki🇬🇧 · Jon-Ivar Skullerud🇮🇪
It is expected that nucleons and their parity partners become degenerate when chiral symmetry is restored. We investigate this question in the context of the thermal transition from the hadronic phase to the quark-gluon plasma, using lattice QCD simulations with N_f=2+1 flavours. We observe a clear sign of parity doubling in the quark-gluon plasma. Besides, we find that the nucleon ground state is, within the uncertainty, largely independent of the temperature, whereas temperature effects are substantial in the negative-parity (N^*) channel, already in the confined phase.
↳ hep-lathep-phnucl-thPRD(2015)·96 citations
10
Mean transverse momenta correlations in hadron-hadron collisions in MC toy model with repulsing strings
Igor Altsybeev🇷🇺
In the present work, Monte-Carlo toy model with repulsing quark-gluon strings in hadron-hadron collisions is described. String repulsion creates transverse boosts for the string decay products, giving modifications of observables. As an example, long-range correlations between mean transverse momenta of particles in two observation windows are studied in MC toy simulation of the heavy-ion collisions.
↳ hep-phnucl-thAIP Conf.Proc.(2016)·14 citations
11
Breakdown of the expansion of finite-size corrections to the hydrogen Lamb shift in moments of charge distribution
Franziska Hagelstein🇩🇪 · Vladimir Pascalutsa (KPH, JGU Mainz)🇩🇪
We quantify a limitation in the usual accounting of the finite-size effects, where the leading $[(Z α)^{4}]$ and subleading $[(Z α)^{5}]$ contributions to the Lamb shift are given by the mean-square radius and the third Zemach moment of the charge distribution. In the presence of any non-smooth behaviour of the nuclear form factor at scales comparable to the inverse Bohr radius, the expansion of the Lamb shift in the moments breaks down. This is relevant for some of the explanations of the "proton size puzzle". We find, for instance, that the de Rújula toy model of the proton form factor does not resolve the puzzle as claimed, despite the large value of the third Zemach moment. Without relying on the radii expansion, we show how tiny, milli-percent (pcm) changes in the proton electric form factor at a MeV scale would be able to explain the puzzle. It shows that one needs to know all the soft contributions to proton electric form factor to pcm accuracy for a precision extraction of the proton charge radius from atomic Lamb shifts.
↳ hep-phnucl-thphysics.atom-phPRA(2015)·13 citations
12
Parton energy loss and momentum broadening at NLO in high temperature QCD plasmas
Jacopo Ghiglieri🇨🇭 · Derek Teaney🇺🇸
We present an overview of a perturbative-kinetic approach to jet propagation, energy loss, and momentum broadening in a high temperature quark-gluon plasma. The leading-order kinetic equations describe the interactions between energetic jet-particles and a non-abelian plasma, consisting of on-shell thermal excitations and soft gluonic fields. These interactions include 2<->2 scatterings, collinear bremsstrahlung, and drag and momentum diffusion. We show how the contribution from the soft gluonic fields can be factorized into a set of Wilson line correlators on the light cone. We review recent field-theoretical developments, rooted in the causal properties of these correlators, which simplify the calculation of the appropriate Wilson lines in thermal field theory. With these simplifications lattice measurements of transverse momentum broadening have become possible, and the kinetic equations describing parton transport have been extended to next-to-leading order in the coupling g.
↳ hep-phnucl-thIJMPE(2015)·59 citations
13
Electromagnetic probes in heavy-ion collisions: Messengers from the hot and dense phase
H. van Hees🇩🇪 · J. Weil🇩🇪 · S. Endres🇩🇪 · M. Bleicher🇩🇪
Due to their penetrating nature, electromagnetic probes, i.e., lepton-antilepton pairs (dileptons) and photons are unique tools to gain insight into the nature of the hot and dense medium of strongly-interacting particles created in relativistic heavy-ion collisions, including hints to the nature of the restoration of chiral symmetry of QCD. Of particular interest are the spectral properties of the electromagnetic current-correlation function of these particles within the dense and/or hot medium. The related theoretical investigations of the in-medium properties of the involved particles in both the partonic and hadronic part of the QCD phase diagram underline the importance of a proper understanding of the properties of various hadron resonances in the medium.
↳ hep-phnucl-thEPJ Web Conf.(2015)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE