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preprint2016arXiv

Ground-state properties of even and odd Magnesium isotopes in a symmetry-conserving approach

We present a self-consistent theory for odd nuclei with exact blocking and particle number and angular momentum projection. The demanding treatment of the pairing correlations in a variation-after-projection approach as well as the explicit consideration of the triaxial deformation parameters in a projection after variation method, together with the use of the finite-range density-dependent Gogny force, provides an excellent tool for the description of odd-even and even-even nuclei. We apply the theory to the Magnesium isotopic chain and obtain an outstanding description of the ground-state properties, in particular binding energies, odd-even mass differences, mass radii and electromagnetic moments among others.

preprint2017arXiv

Chiral potential renormalized in harmonic-oscillator space

We renormalize the chiral effective field theory (EFT) potential in harmonic-oscillator (HO) model space. The low energy constants (LECs) are utilized to absorb not just the ultra-violet part of the physics due to the cutoff, but also the infrared part due to the truncation of model space. We use the inverse J-matrix method to reproduce the nucleon-nucleon (NN) scattering phase shifts in the given model space. We demonstrate that by including the NLO correction, the nucleon-nucleon scattering in the continuum could be well reproduced in the truncated HO trap space up to laboratory energy $T_{lab}=100$ MeV with number of HO basis $n_{max}$ as small as 10. A perturbative power counting starts at subleading order is adopted in this work, and how to extract the perturbative contribution is demonstrated. Our work serves as the input to perform ab-initio calculations.

preprint2016arXiv

Extended Skyrme interactions for nuclear matter, finite nuclei and neutron stars

Recent progress in theory, experiment and observation challenges the mean field models using the conventional Skyrme interaction, suggesting that the extension of the conventional Skyrme interaction is necessary. In this work, by fitting the experimental data of a number of finite nuclei together with a few additional constraints on nuclear matter using the simulated annealing method, we construct three Skyrme interaction parameter sets, namely, eMSL07, eMSL08 and eMSL09, based on an extended Skyrme interaction which includes additional momentum and density dependent two-body forces to effectively simulate the momentum dependence of the three-body force. The three new interactions can reasonably describe the ground-state properties and the isoscalar giant monopole resonance energies of various spherical nuclei used in the fit as well as the ground-state properties of many other spherical nuclei, nicely conform to the current knowledge on the equation of state of asymmetric nuclear matter, eliminate the notorious unphysical instabilities of symmetric nuclear matter and pure neutron matter up to a very high density of $1.2$ fm$^{-3}$, and simultaneously support heavier neutron stars

preprint2016arXiv

Baryon transition form factors at the pole

Electromagnetic resonance properties are uniquely defined at the pole and do not depend on the separation of the resonance from background or the decay channel. Photon-nucleon branching ratios are nowadays often quoted at the pole, and we generalize the considerations to the case of virtual photons. We derive and compare relations for nucleon to baryon transition form factors both for the Breit-Wigner and the pole positions. Using the MAID2007 and SAID SM08 partial wave analyses of pion electroproduction data, we compare the $G_M$, $G_E$, and $G_C$ form factors for the $Δ(1232)$ resonance excitation at the Breit-Wigner resonance and pole positions up to $Q^2=5$ GeV$^2$. We also explore the $E/M$ and $S/M$ ratios as functions of $Q^2$. For pole and residue extraction, we apply the Laurent + Pietarinen method.

preprint2016arXiv

Shape Coexistence in 78 Ni and the new Island of Inversion

Large Scale Shell Model calculations (SM-CI) predict that the region of deformation which comprises the heaviest Chromium and Iron isotopes at and beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the N=20 and N=28 case in the Neon and Magnesium isotopes. We propose a valence space including the full pf-shell for the protons and the full sdg shell for the neutrons; which represents a comeback of the the harmonic oscillator shells in the very neutron rich regime. The onset of deformation is understood in the framework of the algebraic SU3-like structures linked to quadrupole dominance. Our calculations preserve the doubly magic nature of the ground state of 78 Ni, which, however, exhibits a well deformed prolate band at low excitation energy, providing a striking example of shape coexistence far from stability.

preprint2016arXiv

A Hydrodynamic Approach to the Study of Anisotropic Instabilities in Dissipative Relativistic Plasmas

We develop a purely hydrodynamic formalism to describe collisional, anisotropic instabilities in a relativistic plasma, that are usually described with kinetic theory tools. Our main motivation is the fact that coarse-grained models of high particle number systems give more clear and comprehensive physical descriptions of those systems than purely kinetic approaches, and can be more easily tested experimentally as well as numerically. In particular, we aim at developing a theory that describes both a background non-equilibrium fluid configurations and its perturbations, to be able to account for the backreaction of the latter on the former. Our system of equations includes the usual conservation laws for the energy-momentum tensor and for the electric current, and the equations for two new tensors that encode the information about dissipation. To make contact with kinetic theory, we write the different tensors as the moments of a non-equilibrium one-particle distribution function (1pdf) which, for illustrative purposes, we take in the form of a Grad-like ansatz. Although this choice limits the applicability of the formalism to states not far from equilibrium, it retains the main fe

preprint2016arXiv

Perspective on the origin of hadron masses

The energy-momentum tensor in chiral QCD, $T_{μν}$, exhibits an anomaly, viz. $Θ_0 :=T_{μμ} \neq 0$. Measured in the proton, this anomaly yields $m_p^2$, where $m_p$ is the proton's mass; but, at the same time, when computed in the pion, the answer is $m_π^2=0$. Any attempt to understand the origin and nature of mass, and identify observable expressions thereof, must explain and unify these two apparently contradictory results, which are fundamental to the nature of our Universe. Given the importance of Poincaré-invariance in modern physics, the utility of a frame-dependent approach to this problem seems limited. That is especially true of any approach tied to a rest-frame decomposition of $T_{μν}$ because a massless particle does not possess a rest-frame. On the other hand, the dynamical chiral symmetry breaking (DCSB) paradigm, connected with a Poincaré-covariant treatment of the continuum bound-state problem, provides a straightforward, simultaneous explanation of both these identities, and also a diverse array of predictions, testable at existing and proposed facilities. From this perspective, $\langle π| Θ_0 |π\rangle =0$ owing to exact, symmetry-driven cancellations which

preprint2016arXiv

Competition between fermions and bosons in nuclear matter at low densities and finite temperatures

We derive the free energy for fermions and bosons from fragmentation data. Inspired by the symmetry and pairing energy of the Weizsacker mass formula we obtain the free energy of fermions (nucleons) and bosons (alphas and deuterons) using Landau's free energy approach. We confirm previously obtained results for fermions and show that the free energy for alpha particles is negative and very close to the free energy for ideal Bose gases. Deuterons behave more similarly to fermions (positive free energy) rather than bosons. This is due to their low binding energy, which makes them very 'fragile', i.e., easily formed and destroyed. We show that the α-particle fraction is dominant at all temperatures and densities explored in this work. This is consistent with their negative free energy, which favors clusterization of nuclear matter into α-particles at subsaturation densities and finite temperatures. The role of finite open systems and Coulomb repulsion is addressed.

preprint2017arXiv

Quark mass dependence of H-dibaryon in $ΛΛ$ scattering

We study the quark mass dependence of the H-dibaryon in the strangeness $S=-2$ baryon-baryon scattering. A low-energy effective field theory is used to describe the coupled-channel scattering, in which the quark mass dependence is incorporated so as to reproduce the lattice QCD data by the HAL QCD collaboration in the SU(3) limit. We point out the existence of the Castillejo-Dalitz-Dyson (CDD) pole in the $ΛΛ$ scattering amplitude below the threshold in the SU(3) limit, which may cause the Ramsauer-Townsend effect near the $NΞ$ threshold at the physical point. The H-dibaryon is unbound at the physical point, and a resonance appears just below the $NΞ$ threshold. As a consequence of the coupled-channel dynamics, the pole associated with the resonance is not continuously connected to the bound state in the SU(3) limit. Through the extrapolation in quark masses, we show that the unitary limit of the $ΛΛ$ scattering is achieved between the physical point and the SU(3) limit. We discuss the possible realization of the "H-matter" in the unphysical quark mass region.

preprint2016arXiv

Experimental investigation of a linear-chain structure in the nucleus 14C

It is a well-known fact that a cluster of nucleons can be formed in the interior of an atomic nucleus, and such clusters may occupy molecular-like orbitals, showing characteristics similar to normal molecules consisting of atoms. Chemical molecules having a linear alignment are commonly seen in nature, such as carbon dioxide. A similar linear alignment of the nuclear clusters, referred to as linear-chain cluster state (LCCS), has been studied since the 1950s, however, up to now there is no clear experimental evidence demonstrating the existence of such a state. Recently, it was proposed that an excess of neutrons may offer just such a stabilizing mechanism, revitalizing interest in the nuclear LCCS, specifically with predictions for their emergence in neutron-rich carbon isotopes. Here we present the experimental observation of α-cluster states in the radioactive 14C nucleus. Using the 10Be+α resonant scattering method with a radioactive beam, we observed a series of levels which completely agree with theoretically predicted levels having an explicit linear-chain cluster configuration. We regard this as the first strong indication of the linear-chain clustered nucleus.

preprint2016arXiv

Photoproduction of hidden-charm states in the $γp \to \bar{D}^{*0} Λ^+_c$ reaction near threshold

We report on a theoretical study of the hidden charm $N^*_{c \bar{c}}$ states in the $γp \to \bar{D}^{*0} Λ^+_c$ reaction near threshold within an effective Lagrangian approach. In addition to the contributions from the $s$-channel nucleon pole, the $t$-channel $D^0$ exchange, the $u$-channel $Λ^+_c$ exchange and the contact term, we study the contributions from the $N^*_{c \bar{c}}$ states with spin-parity $J^P = 1/2^-$ and $3/2^-$. The total and differential cross sections of the $γp \to \bar{D}^{*0} Lambda^+_c$ reaction are predicted. It is found that the contributions of these $N^*_{c \bar{c}}$ states give clear peak structures in the total cross sections. Thus, this reaction is another new platform to study the hidden-charm states. It is expected that our model calculation may be tested by the future experiments.

preprint2016arXiv

Production of $ΛΛ$ and $\bar{Λ\text{n}}$ in central Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV within a covariant coalescence model

We study the production of $ΛΛ$ and $\overline{Λ\text{n}}$ exotic states in central Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV at LHC via both hadron and quark coalescence within a covariant coalescence model with a blast-wave-like parametrization for the phase-space configurations of constituent particles at freezeout. In the hadron coalescence, the two states are considered as molecular states while they are considered as six-quark states in the quark coalescence.For $\overline{Λ\text{n}}$, we find that the yields of both molecular and six-quark states are much larger than the experimental upper-limits. For $ΛΛ$, while the molecule-state yield is much larger than the experimental upper-limits, the six-quark-state yield could be lower than the upper-limits. The higher molecule-state yields are mainly due to the large contribution of short-lived strong resonance decays into (anti-)nucleons and (anti-)$Λ$ which can significantly enhance the molecule-state yields of $ΛΛ$ and $\overline{Λ\text{n}}$ via hadron coalescence. Our results suggest that the current experimental measurement at LHC cannot exclude the existence of the $ΛΛ$ as an exotic six-quark state, and if $ΛΛ$ is a six-qu

preprint2016arXiv

Effects of entrance channel on fusion probability in hot fusion reactions

Within the framework of the dinuclear system (DNS) model, the fusion reactions leading to the compound nuclei 274Hs and 286Cn are investigated. The fusion probability as a function of DNS excitation energy is studied. The calculated results are in good agreement with the available experimental data. The obtained results show that the fusion probabilities are obviously enhanced for the reactions located at high place in potential energy surface, although these reactions may have small values of mass asymmetry. It is found that the enhancement is due to the large potential energy of the initial DNS.

preprint2016arXiv

Efectos de Temperatura Finita y Curvatura en QCD y Modelos de Quarks Quirales

We develop the heat kernel method in the context of finite temperature quantum field theory. We compute the heat kernel expansion in the presence of general gauge and scalar fields which may be non Abelian and non stationary. The Polyakov loop appears at finite temperature as a new gauge covariant operator. We apply this method in the computation of the fully gauge invariant effective action of QCD in the regime of high temperature. It is obtained the dimensionally reduced effective action of QCD as well. In the context of chiral quark models, in particular the Nambu--Jona-Lasinio and the spectral quark model, we apply this method to compute the low-energy chiral Lagrangian at finite temperature. The coupling of the Polyakov loop with these models allows to solve some inconsistencies appearing in the standard treatment at finite temperature: generation of multi-quark states, large $N_c$ counting, etc. On the other hand, we show that recent available lattice data for the renormalized Polyakov loop above the deconfinement phase transition exhibit unequivocal inverse power temperature corrections driven by a dimension 2 gluon condensate. This simple ansatz provides a good overall desc

preprint2016arXiv

Capture cross sections of 15N(n, γ)16N at astrophysical energies

We have reanalyzed reaction cross sections of 16N on 12C target. The nucleon density distribution of 16N, especially surface density distribution, was extracted using the modified Glauber model. On the basis of dilute surface densities, the discussion of 15N(n, γ)16N reaction was performed within the framework of the direct capture reaction mechanism. The calculations agreed quite well with the experimental data.

preprint2016arXiv

Helicity and nuclear $β$ decay correlations

We present simple derivations of nuclear $β$-decay correlations with an emphasis on the special role of helicity. This provides a good opportunity to teach students about helicity and chirality in particle physics through exercises using simple aspects of quantum mechanics. In addition, this paper serves as an introduction to nuclear $β$-decay correlations from both a theoretical and experimental vantage. This article can be used to introduce students to ongoing experiments searching for hints of new physics in the low-energy precision frontier.

preprint2016arXiv

Multi-Regulator Functional Renormalization Group for Many-Fermion Systems

We propose a method of multi-regulator functional renormalization group (MR-FRG) which is a novel formulation of functional renormalization group with multiple infrared regulators. It is applied to a two-component fermionic system with an attractive contact interaction to study crossover phenomena between the Bardeen-Cooper-Schrieffer (BCS) phase and the Bose-Einstein condensation (BEC) phase. To control both the fermionic one-particle excitations and the bosonic collective excitations,IR regulators are introduced, one for the fermionic two-point function and another for the four-fermion vertex. It is shown that the Nozières-Schmitt-Rink (NSR) theory, which is successful to capture qualitative features of the BCS-BEC crossover, can be derived from MR-FRG. Some aspects of MR-FRG to go beyond the NSR theory are also discussed.

preprint2016arXiv

From the pion cloud of Tomonaga to the electron pairs of Schrieffer: many body wave functions from nuclear physics to condensed matter physics

It is well known that diverse pieces of models and physical ideas coming from different areas of physics converged in the BCS theory of superconductivity. On the contrary it is little known that the formalism developed in the Tomonaga quantum field theory of the pion-nucleon system was an important ingredient for the development of BCS theory. We discuss the evolution of these ideas in quantum field theory providing an unconventional historical perspective.

preprint2016arXiv

Geometrical Clusterization in SU(2) gluodynamics and Liquid-gas Phase Transition

The liquid droplet formula is applied to an analysis of the properties of geometrical (anti)clusters formed in SU(2) gluodynamics by the Polyakov loops of the same sign. Using this approach, we explain the phase transition in SU(2) gluodynamics as a transition between two liquids during which one of the liquid droplets (the largest cluster of a certain Polyakov loop sign) experiences a condensation, while another droplet (the next to the largest cluster of the opposite sign of Polyakov loop) evaporates. The clusters of smaller sizes form two accompanying gases, which behave oppositely to their liquids. The liquid droplet formula is used to analyze the size distributions of the gas (anti)clusters. The fit of these distributions allows us to extract the temperature dependence of surface tension and the value of Fisher topological exponent $τ$ for both kinds of gaseous clusters. It is shown that the surface tension coeficient of gaseous (anti)clusters can serve as an order parameter of the deconfinement phase transition in SU(2) gluodynamics. The Fisher topological exponent $τ$ of (anti)clusters is found to have the same value $1.806 \pm 0.008$. This value disagrees with the famous Fi

preprint2016arXiv

Antisymmetrized molecular dynamics studies for exotic clustering phenomena in neutron-rich nuclei

We present a review of recent works on clustering phenomena in unstable nuclei studied by antisymmetrized molecular dynamics (AMD). The AMD studies in these decades have uncovered novel types of clustering phenomena brought about by the excess neutrons. Among them, this review focuses on the molecule-like structure of unstable nuclei. One of the earliest discussions on the clustering in unstable nuclei was made for neutron-rich Be and B isotopes. AMD calculations predicted that the ground state clustering is enhanced or reduced depending on the number of excess neutrons. Today, the experiments are confirming this prediction as the change of the proton radii. Behind this enhancement and reduction of the clustering, there are underlying shell effects called molecular- and atomic-orbits. These orbits form covalent and ionic bonding of the clusters analogous to the atomic molecules. It was found that this "molecular-orbit picture" reasonably explains the low-lying spectra of Be isotopes. The molecular-orbit picture is extended to other systems having parity asymmetric cluster cores and to the three cluster systems. O and Ne isotopes are the candidates of the former, while the $

preprint2016arXiv

Bohr Hamiltonian for gamma=0 with Davidson Potential

A gamma-rigid solution of the Bohr Hamiltonian is derived for gamma=0 utilizing the Davidson potential in the beta variable. This solution is going to be called X(3)-D. The energy eigenvalues and wave functions are obtained by using an analytic method which has been developed by Nikiforov and Uvarov. BE(2) transition rates are calculated. A variational procedure is applied to energy ratios to determine whether or not the X(3) model is located at the critical point between spherical and deformed nuclei.

preprint2016arXiv

Evolution to the Quark-Gluon Plasma

Theoretical studies on the early-time dynamics in the ultra-relativistic heavy-ion collisions are reviewed including pedagogical introductions on the initial condition with small-x gluons treated as a color glass condensate, the bottom-up thermalization scenario, plasma/glasma instabilities, basics of some formulations such as the kinetic equations and the classical statistical simulation. More detailed discussions follow to make an overview of recent developments on the fast isotropization, the onset of hydrodynamics, and the transient behavior of momentum spectral cascades.

preprint2016arXiv

Evidence of the mixed phase formation in nucleus-nucleus collisions

Searchers for various irregularities in the behavior of thermodynamic quantities at chemical freeze-out (CFO) are rather important in a view of experimental studies of quark-gluon plasma (QGP). Using the multicomponent hadron resonance gas model (HRGM), developed in (Sagun, 2014; Bugaev et al., 2015), we performed a high-quality fit of 111 hadronic ratios measured for 14 values of the center of mass collision energies between 2.7 GeV and 200 GeV with the overall fit quality $χ^2/dof \simeq 0.95$. In addition to previously reported singularities (Bugaev et al., 2015) at CFO we found that the hadron yield ratios $\fracΛ{p}$, $\frac{K^{+}}{p}$, $\frac{K^{+}}Λ$, $\frac{Ω^{-}}{p}$ and $\frac{Ξ^{-}}{p}$ measured in central nuclear collisions demonstrate a significant change of slope in the same range of center of mass collision energy $\sqrt{s_{NN}} = 4.3-4.9$ GeV (Bugaev et al., 2015). This change of slopes is accompanied by a dramatic increase of resonance decays at CFO. Also at CFO the trace anomaly and baryonic density demonstrate the pronounced peaks at the collision energy $\sqrt{s_{NN}} = 4.9 $ GeV. We argue that all these and previously found irregularities provide an evidence fo

preprint2017arXiv

Structure effects on fission yields

The structure effects of the fission fragments on their yields are studied within the statical theory with the inputs, like, excitation energies and level density parameters for the fission fragments at a given temperature calculated using the temperature dependent relativistic mean field formalism (TRMF). For the comparison, the results are also obtained using the finite range droplet model. At temperatures $T =1-2$ MeV, the structural effects of the fission fragments influence their yields. It is also seen that at $T = $ 3 MeV, the fragments become spherical and the fragments distribution peaks at a close shell or near close shell nucleus.

1027 works