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G. E. Brown

Publications and source records attributed to G. E. Brown.

At least 37 records · Page 2Linked to original sources
arXiv2005

Low-momentum Hyperon-Nucleon Interactions

We present a first exploratory study for hyperon-nucleon interactions using renormalization group techniques. The effective two-body low-momentum potential V_low-k is obtained by integrating out the high-momentum components from realistic Nijmegen YN potentials. A T-matrix equivalence approach is employed, so that the low-energy phase shifts are reproduced by V_low-k up to a momentum scale Lambda ~ 500 MeV. Although the various bare Nijmegen models differ somewhat from each other, the corresponding V_low-k interactions show convergence in some channels, suggesting a possible unique YN interaction at low momenta.

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arXiv2005

Low momentum shell model effective interactions with all-order core polarizations

An all-order summation of core polarization diagrams using the low-momentum nucleon-nucleon interaction, V_low-k is presented. The summation is based on the Kirson-Babu-Brown (KBB) induced interaction approach in which the vertex functions are obtained self consistently by solving a set of non-linear coupled equations. It is found that the solution of these equations is simplified by using V_low-k, which is energy independent, and by employing Green functions in the particle-particle and particle-hole channels. We have applied this approach to the sd-shell effective interactions and find that the results calculated to all orders using the KBB summation technique are remarkably similar to those of second-order perturbation theory, average differences being less than 10%.

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arXiv2004

Generalized Seniority Description of Cold Fermi Gases

We suggest that the extension of the Racah seniority description of strongly interacting fermions in the nuclear shell model is directly generalizable to describe pairing of atoms in cold Fermi systems. We illustrate this by the fermionic pairing in the much studied cold two-component gas of Li atoms. Our pairing interaction is two orders of magnitude stronger than that used in the usual BCS approach. We also explain why the Racah scheme is less applicable to nuclei, and discuss the similarities of the strongly-coupled matter in cold fermion systems and the new form of matter found in RHIC close to T_c.

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arXiv2004

Separation of Scales in the More Effective Field Theory and Moszkowski-Scott Methods

We compare the momentum-space decimation procedure used to construct the low momentum nucleon-nucleon interaction V(low-k) with the configuration-space separation method of Moszkowski and Scott. Each procedure defines a separation of scales in the nuclear many-body problem, and the extent to which these two scales coincide is studied. By studying the effects of the separation method on the relative S-state Kallio-Kolltveit potential, it is found that close agreement with V(low-k) is obtained as the configuration-space cutoff is lowered to ~ 1.0 fm.

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arXiv2004

Chemical Equilibration in Relativistic Heavy Ion Collisions

In the hadronic sector of relativistic heavy ion physics, the $ρ<=> 2π$ reaction is the strongest one, strong enough to equilibrate the $ρ$ with the pions throughout the region from chemical freezeout to thermal freezeout when free-particle interactions (with no medium-dependent effects) are employed. Above the chiral restoration temperature, only $ρ$'s and $π$'s are present, in that the chirally restored $A_1$ is equivalent to the $ρ$ and the mesons have an SU(4) symmetry, with no dependence on isospin and negligible dependence on spin. In the same sense the $σ$ and $π$ are "equivalent" scalars. Thus the chirally restored $ρ\leftrightarrows 2π$ exhaust the interspecies transitions. We evaluate this reaction at $T_c$ and find it to be much larger than below $T_c$, certainly strong enough to equilibrate the chirally restored mesons just above $T_c$. When emitted just below $T_c$ the mesons remain in equilibrium, at least in the chiral limit because of the Harada-Yamawaki "vector manifestation" that requires that mesonic coupling constants go to zero (in the chiral limit) as $T$ goes to $T_c$ from below. Our estimates in the chiral limit give deviations in some particle ratios from the standard scenario (of equilibrium in the hadronic sector just below $T_c$) of about double those indicated experimentally. This may be due to the neglect of explicit chiral symmetry breaking in our estimates. We also show that the instanton molecules present above $T_c$ are the giant multipole vibrations found by Asakawa, Hatsuda and Nakahara and of Wetzorke et al. in lattice gauge calculations. Thus, the matter formed by RHIC can equivalently be called: chirally restored mesons, instanton molecules, or giant collective vibrations. It is a strongly interacting liquid.

hep-ph↗
arXiv2004

Medium Modifications of Charm and Charmonium in High-Energy Heavy-Ion Collisions

The production of charmonia in heavy-ion collisions is investigated within a kinetic theory framework simultaneously accounting for dissociation and regeneration processes in both quark-gluon plasma (QGP) and hadron-gas phases of the reaction. In-medium modifications of open-charm states (c-quarks, D-mesons) and the survival of J/psi mesons in the QGP are included as inferred from lattice QCD. Pertinent consequences on equilibrium charmonium abundances are evaluated and found to be especially relevant to explain the measured centrality dependence of the psi'/psi ratio at SPS. Predictions for recent In-In experiments, as well as comparisons to current Au-Au data from RHIC, are provided.

hep-ph↗
arXiv2004

The Instanton Molecule Liquid and "Sticky Molasses" Above T_c

The main objective of this work is to explore the evolution in the structure of the quark-antiquark bound states in going down in the chirally restored phase from the so-called "zero binding points" T_zb to the QCD critical temperature T_c at which the Nambu-Goldstone and Wigner-Weyl modes meet. In doing this, we adopt the idea recently introduced by Shuryak and Zahed for charmed $\bar c c$, light-quark $\bar q q$ mesons $π, σ, ρ, A_1$ and gluons that at T_zb, the quark-antiquark scattering length goes through infinity at which conformal invariance is restored, thereby transforming the matter into a near perfect fluid behaving hydrodynamically, as found at RHIC. We show that the binding of these states is accomplished by the combination of (i) the color Coulomb interaction, (ii) the relativistic effects, and (iii) the interaction induced by the instanton-anti-instanton molecules. The spin-spin forces turned out to be small. While near T_zb all mesons are large-size nonrelativistic objects bound by Coulomb attraction, near T_c they get much more tightly bound, with many-body collective interactions becoming important and making the $σ$ and $π$ masses approach zero (in the chiral limit). The wave function at the origin grows strongly with binding, and the near-local four-Fermi interactions induced by the instanton molecules play an increasingly more important role as the temperature moves downward toward T_c.

hep-ph↗
arXiv2003

Counter Terms for Low Momentum Nucleon-Nucleon Interactions

There is much current interest in treating low energy nuclear physics using the renormalization group (RG) and effective field theory (EFT). Inspired by this RG-EFT approach, we study a low-momentum nucleon-nucleon (NN) interaction, V_{low-k}, obtained by integrating out the fast modes down the scale ~2fm^{-1}. Since NN experiments can only determine the effective interaction in the low momentum region, our chief purpose is to find such an interaction for complex nuclei whose typical momenta lie below this scale. In this paper we find that V_{low-k} can be satisfactorily accounted for by the counter terms corresponding to a short range effective interaction. The coefficients C_n of the power series expansion C_n*k^n for the counter terms have been accurately determined and results derived from several meson-exchange NN interaction models are compared. The counter terms are found to be important for the S, P, and D partial waves. Scaling behavior of the counter terms is also studied, and we discuss the use of these methods for computing shell model matrix elements.

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arXiv2003

Family of Hermitian Low-Momentum Nucleon Interactions with Phase Shift Equivalence

Using a Schmidt orthogonalization transformation, a family of Hermitian low-momentum NN interactions is derived from the non-Hermitian Lee-Suzuki (LS) low-momentum NN interaction. As special cases, our transformation reproduces the Hermitian interactions for Okubo and Andreozzi. Aside from their common preservation of the deuteron binding energy, these Hermitian interactions are shown to be phase shift equivalent, all preserving the empirical phase shifts up to decimation scale Lambda. Employing a solvable matrix model, the Hermitian interactions given by different orthogonalization transformations are studied; the interactions can be very different from each other particularly when there is a strong intruder state influence. However, because the parent LS low-momentum NN interaction is only slightly non-Hermitian, the Hermitian low-momentum nucleon interactions given by our transformations, including the Okubo and Andreozzi ones, are all rather similar to each other. Shell model matrix elements given by the LS and several Hermitian low-momentum interactions are compared.

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arXiv2003

In-Medium Effects on Charmonium Production in Heavy-Ion Collisions

Charmonium production in heavy-ion collisions is investigated within a kinetic theory framework incorporating in-medium properties of open- and hidden-charm states in line with recent QCD lattice calculations. A continuously decreasing open-charm threshold across the phase boundary of hadronic and quark-gluon matter is found to have important implications for the equilibrium abundance of charmonium states. The survival of $J/ψ$ resonance states above the transition temperature enables their recreation also in the Quark-Gluon Plasma. Including effects of chemical and thermal off-equilibrium, we compare our model results to available experimental data at CERN-SPS and BNL-RHIC energies. In particular, earlier found discrepancies in the $ψ'/ψ$ ratio can be resolved.

hep-ph↗
arXiv2003

Nature of the Chiral Restoration Transition in QCD

As the chirally restored phase ends with T coming down to T_c, a phase resembling a mixed phase is realized, during which the hadrons (which are massless at T_c in the chiral limit) get their masses back out of their kinetic energy. The gluon condensation energy is fed into the system to keep the temperature (nearly) constant. Lattice results for the gluon condensation are matched by a Nambu-Jona-Lasinio calculation. The latter shows that below T_c the chiral symmetry is barely broken, so that with an about 6% drop in the scalar coupling G it is restored at T_c. Nearly half of the glue, which we call epoxy, is not melted at T_c.

hep-ph↗
arXiv2003

Double Decimation and Sliding Vacua in the Nuclear Many-Body System

We propose that effective field theories for nuclei and nuclear matter comprise of "double decimation": (1) the chiral symmetry decimation (CSD) and (2) Fermi liquid decimation (FLD). The Brown-Rho scaling recently identified as the parametric dependence intrinsic in the "vector manifestation" of hidden local symmetry theory of Harada and Yamawaki results from the first decimation. This scaling governs dynamics down to the scale at which the Fermi surface is formed as a quantum critical phenomenon. The next decimation to the top of the Fermi sea where standard nuclear physics is operative makes up the Fermi liquid decimation. Thus nuclear dynamics is dictated by two fixed points, namely, the vector manifestation fixed point and the Fermi liquid fixed point. It has been a prevalent practice in nuclear physics community to proceed with the second decimation only, assuming density independent masses. We show why most nuclear phenomena can be reproduced by theories using either density-independent, or density-dependent masses, a grand conspiracy of nature that is an aspect that could be tied to the Cheshire-Cat phenomenon in hadron physics. We identify what is left out in the Fermi liquid decimation that does not incorporate the CSD. Experiments such as the dilepton production in relativistic heavy ion reactions, which are specifically designed to observe effects of dropping masses, could exhibit large effects from the reduced masses. However they are compounded with effects that are not directly tied to chiral symmetry. We discuss a recent STAR/RHIC observation where BR scaling can be singled out in a pristine environment.

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arXiv2003

Matching the QCD and Hadron Sectors and Medium Dependent Meson Masses; Hadronization in Relativistic Heavy Ion Collisions

The recent developments on the "vector manifestation" of chiral symmetry by Harada and Yamawaki provide a compelling evidence for, and "refine," the in-medium scaling of hadronic properties in dense/hot matter (call it ``BR scaling") proposed by the authors in 1991. We reinterpret the Harada-Yamawaki result obtained in a Wilsonian renormalization-group approach to hidden local symmetry theory matched to QCD at near the chiral scale in terms of the Nambu-Jona-Lasinio model and predict that the vector meson mass in medium should scale $m_ρ^\star/m_ρ\sim (\la\bar{q}q\ra^\star/\la\bar{q}q\ra)^{1/2}$ from $n=0$ up to $\sim n=n_0$ (where $n_0$ is nuclear matter density) and then go over to the linear scaling $m_ρ^\star/m_ρ\sim \la\bar{q}q\ra^\star/\la\bar{q}q\ra$ up to the chiral transition density $n_c$ at which the mass is to vanish (in the chiral limit) according to the vector manifestation fixed point. In the regime of the linear scaling above $n_0$, the (vector) gauge coupling constant should fall linearly in $\la\bar{q}q\ra^\star$, vanishing at the critical point, with the width of the vector meson becoming steeply narrower. We suggest the in-medium vector meson mass, {\em both} parametric and pole, which goes smoothly to zero with increasing density, to be an order parameter for chiral symmetry restoration. Some issues related to recent RHIC observations are qualitatively discussed in the appendices. Our main conclusion that follows from these considerations is that the movement towards chiral restoration can be reliably described in Nambu-Jona-Lasinio mean field, with constituent quarks as variables, although there is probably density discontinuity following chiral restoration.

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arXiv2003

Renormalization Group Methods for the Nuclear Many-Body Problem

The application of renormalization group methods to microscopic nuclear many-body calculations is discussed. We present the solution of the renormalization group equations in the particle-hole channels for neutron matter and the application to S-wave pairing. Furthermore, we point out that the inclusion of tensor and spin-orbit forces leads to spin non-conserving effective interactions in nuclear matter.

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arXiv2002

Matter-induced modification of resonances at RHIC freezeout

We discuss the physical effects causing a modification of resonance masses, widths and even shapes in a dilute hadronic gas at late stages of heavy ion collisions. We quantify the conditions at which resonances are produced at RHIC, and found that it happens at $T\approx 120 MeV$. Although in the pp case the ``kinematic'' effects like thermal weighting of the states is sufficient, in AA we see a clear effect of dynamical interaction with matter, both due to a variety of s-channel resonances and due to t-channel scalar exchanges. The particular quantity we focus mostly on is the $ρ$ meson mass, for which these dynamical effects lead to about -50 MeV shift, on top of about -20 MeV of a thermal effect: both agree well with preliminary data from STAR experiment at RHIC. We also predict a complete change of shape of $f_0(600)$ resonance, even by thermal effects alone.

hep-ph↗
arXiv2002

The nucleon interaction and neutron matter from the renormalization group

We show that the renormalization group decimation of modern nucleon potential models to low momenta results in a unique nucleon interaction V_{low k}. This interaction is free of short-ranged singularities and can be used directly in many-body calculations. The RG scaling properties follow directly from the invariance of the scattering phase shifts. We discuss the RG treatment of Fermi liquids. The RG equation for the scattering amplitude in the two particle-hole channels is given at zero temperature. The flow equations are simplified by retaining only the leading term in an expansion in small momentum transfers. The RG flow is illustrated by first studying a system of spin-polarized fermions in a simple model. Finally, results for neutron matter are presented by employing the unique low momentum interaction V_{low k} as initial condition of the flow. The RG approach yields the amplitude for non-forward scattering, which is of great interest for calculations of transport properties and superfluid gaps in neutron star interiors. The methods used can also be applied to condensed matter systems in the absence of long-ranged interactions.

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arXiv2002

Discovery of a Black-hole Mass - Period Correlation in Soft X-ray Transients and its Implication for Gamma-Ray Burst and Hypernova Mechanisms

We investigate the soft X-ray transients with black hole primaries which may have been the sources of gamma-ray bursts and hypernovae earlier in their evolution. We find that the black-hole mass increases with the orbital period of the binary, both for systems with main-sequence donors and for those with evolved donors. This correlation can be understood in terms of angular-momentum support in the helium star progenitor of the black hole, if the systems with shorter periods had more rapidly rotating primaries prior to their explosion: centrifugal support will then prevent more of its mass from collapsing into the black hole. This trend of more rapidly rotating stars in closer binaries is very generally seen, and in the present case can be understood in terms of spin-up during spiral in and subsequent tidal coupling. We investigate the relation quantitatively and obtain reasonable agreement with the observed mass-period correlation. A natural consequence of this observation is that black holes formed in soft X-ray transients acquire significant Kerr parameters. This makes them good sources of power for gamma-ray bursts and hypernovae, via the Blandford-Znajek mechanism, and thus supports our model for the origin of gamma-ray bursts in soft X-ray transients.

astro-ph↗