Chang-Hwan Lee

West Virginia University, Morgantown, West Virginia, United States

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Publications (58)191.15 Total impact

  • Source
    Soomin Jeong, Chang-Hwan Lee
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    ABSTRACT: Gamma ray bursts have been divided into two classes, long-soft gamma ray burst and short-hard gamma ray burst according to the bimodal distribution in duration time. Due to the harder spectrum and the lack of afterglows of short-hard bursts in optical and radio observations, different progenitors for short-hard bursts and long-soft bursts have been suggested. Based on the X-ray afterglow observation and the cumulative red-shift distribution of short-hard bursts, Nakar et al. (2006) found that the progenitors of short-hard bursts are consistent with old populations, such as mergers of binary neutron stars. Recently, the existence of two subclasses in long-soft bursts has been suggested after considering multiple characteristics of gamma-ray bursts, including fluences and the duration time. In this work, we extended the analysis of cumulative red-shift distribution to two possible subclasses in L-GRBs. We found that two possible subclass GRBs show different red-shift distributions, especially for red-shifts z > 1. Our results indicate that the accumulative red-shift distribution can be used as a tool to constrain the progenitor characteristics of possible subclasses in L-GRBs.
    11/2007;
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    ABSTRACT: Recent developments in our description of RHIC and related heavy-ion phenomena in terms of hidden local symmetry theories are reviewed with a focus on the novel nearly massless states in the vicinity of—both below and above—the chiral restoration temperature Tc. We present complementary and intuitive ways to understand both Harada–Yamawaki's vector manifestation structure and Brown–Rho scaling—which are closely related—in terms of “melting” of soft glues observed in lattice calculations and join the massless modes that arise in the vector manifestation (in the chiral limit) just below Tc to tightly bound massless states above Tc. This phenomenon may be interpreted in terms of the Bèg–Shei theorem. It is suggested that hidden local symmetry theories arise naturally in holographic dual QCD from string theory, and a clear understanding of what really happens near the critical point could come from a deeper understanding of the dual bulk theory. Other matters discussed are the relation between Brown–Rho scaling and Landau Fermi-liquid fixed point parameters at the equilibrium density, its implications for “low-mass dileptons” produced in heavy-ion collisions, the reconstruction of vector mesons in peripheral collisions, the pion velocity in the vicinity of the chiral transition point, kaon condensation viewed from the VM fixed point, nuclear physics with Brown–Rho scaling, and the generic feature of dropping masses at the RGE fixed points in generalized hidden local symmetry theories.
    Physics Reports 01/2007; · 22.93 Impact Factor
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    Hans A. Bethe, Gerald E. Brown, Chang-Hwan Lee
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    ABSTRACT: In the light of recent observations in which short γ-ray bursts are interpreted as arising from black-hole(BH), neutron-star(NS) or NS–NS mergings we would like to review our research on the evolution of compact binaries, especially those containing NS's. These were carried out with predictions for LIGO in mind, but are directly applicable to short γ-ray bursts in the interpretation above.Most important in our review is that we show that the standard scenario for evolving NS–NS binaries always ends up with a low-mass BH (LMBH), NS binary. Bethe and Brown [1998, Astrophys. J. 506, 780] showed that this fate could be avoided if the two giants in the progenitor binary burned He at the same time, and that in this way the binary could avoid the common envelope evolution of the NS with red giant companion which sends the first born NS into a BH in the standard scenario. The burning of He at the same time requires, for the more massive giants such as the progenitors of the Hulse–Taylor binary NS that the two giants be within 4% of each other in zero age main sequence (ZAMS) mass. Applying this criterion to all binaries results in a factor ∼5 of LMBH–NS binaries as compared with NS–NS binaries.Although this factor is substantially less than the originally claimed factor of 20 which Bethe and Brown (1998) estimated, largely because a careful evolution has been carried through here, our factor 5 is augmented by a factor of ∼8 arising from the higher rate of star formation in the earlier Galaxy from which the BH–NS binaries came from. Furthermore, here we calculate the mergers for short-hard gamma-ray bursts, whereas Bethe and Brown's factor 20 included a factor of 2 for the higher chirp masses in a BH–NS binary as compared with NS–NS one. In short, we end up with an estimate of factor ∼40 over that calculated with NS–NS binary mergers in our Galaxy alone. Our total rate is estimated to be about one merging of compact objects per year.Our scenario of NS–NS binaries as having been preceded by a double He-star binary is collecting observational support in terms of the nearly equal NS masses within a given close binary.We review our work on population synthesis of compact binaries, pointing out that it is in excellent agreement with the much more detailed synthesis carried out by Portegies Zwart. This is currently of interest because the recent discovery of the double pulsar has substantially increased the number of binary NS's that will merge gravitationally, giving signals to LIGO. This discovery brings in the low ZAMS mass main sequence progenitors that can evolve into a NS binary, adding importantly to the “visible” binaries that can merge. However it does not affect the factor ≳40 increase, mostly from the much greater number of LMBH–NS binaries, which have only a small probability of being observed before they merge.We develop the phenomenology which suggests that NS's evolve from ZAMS mass ∼10–18M⊙ star, LMBH's from 18–20M⊙, and high-mass BH's from 20–30M⊙. These brackets follow from Woosley's 12C(α,γ)16O rate of 170 MeV barns at 300 keV.We discuss the observed violation of our previous maximum NS mass , raising our to 1.7M⊙ and comment on how our scenario would change if the maximum NS mass is greater than 1.7M⊙.
    Physics Reports 01/2007; · 22.93 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent developments in our description of RHIC and related heavy-ion phenomena in terms of hidden local symmetry theories are reviewed with a focus on the novel nearly massless states in the vicinity of -- both below and above -- the chiral restoration temperature T_c. We present complementary and intuitive ways to understand both Harada-Yamawaki's vector manifestation structure and Brown-Rho scaling -- which are closely related -- in terms of "melting" of soft glues observed in lattice calculations and join the massless modes that arise in the vector manifestation (in the chiral limit) just below T_c to tightly bound massless states above T_c. This phenomenon may be interpreted in terms of the Beg-Shei theorem. It is suggested that hidden local symmetry theories arise naturally in holographic dual QCD from string theory, and a clear understanding of what really happens near the critical point could come from a deeper understanding of the dual bulk theory. Other matters discussed are the relation between Brown-Rho scaling and Landau Fermi-liquid fixed point parameters at the equilibrium density, its implications for "low-mass dileptons" produced in heavy-ion collisions, the reconstruction of vector mesons in peripheral collisions, the pion velocity in the vicinity of the chiral transition point, kaon condensation viewed from the VM fixed point, nuclear physics with Brown-Rho scaling, and the generic feature of dropping masses at the RGE fixed points in generalized hidden local symmetry theories.
    09/2006;
  • G. E. Brown, Chang-Hwan Lee, Mannque Rho
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    ABSTRACT: The vector manifestation (VM) fixed-point scenario found in the Harada-Yamawaki hidden local symmetry effective theory makes a striking prediction that as the fireball expands and cools from Tc down toward the freeze-out temperature Tfreeze-out in heavy-ion collisions, what we refer to as “hadronic freedom” sets in which hadrons do not interact or barely interact. We suggest that this scenario is testable at the BNL relativistic heavy in collider, and as a specific example, we provide an astonishingly simple prediction in terms of the V.M for the ρ0/π- ratio measured in peripheral collisions. We suggest that this hadronic freedom has already been observed in the STAR peripheral collisions, in which the ρ0 mesons were reconstructed by following their pion decay products back to the vertex where they are formed. In this scenario, the measured ρ0/π- ratio can be reproduced in these special circumstances only because the “flash temperature” Tflash at which the ρ mesons go on-shell is equal to the freeze-out temperature. In more central collisions with lower freeze-out temperatures, the rescattering of the pions is expected to destroy the possibility of this reconstruction.
    Physical Review C 08/2006; 74(2). · 3.72 Impact Factor
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    G E Brown, Chang-Hwan Lee, Hong-Jo Park, Mannque Rho
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    ABSTRACT: Building on, and extending, the result of a higher-order in-medium chiral perturbation theory combined with renormalization group arguments and a variety of observations of the vector manifestation of Harada-Yamawaki hidden local symmetry theory, we obtain a surprisingly simple description of kaon condensation by fluctuating around the "vector manifestation" fixed point identified to be the chiral restoration point. Our development establishes that strangeness condensation takes place at approximately 3n0 where n0 is nuclear matter density. This result depends only on the renormalization-group (RG) behavior of the vector interactions, other effects involved in fluctuating about the bare vacuum in so many previous calculations being irrelevant in the RG about the fixed point. Our results have major effects on the collapse of neutron stars into black holes.
    Physical Review Letters 03/2006; 96(6):062303. · 7.73 Impact Factor
  • Hans A. Bethe, Gerald E. Brown, Chang-Hwan Lee
    Hans Bethe and his Physics. 01/2006;
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    ABSTRACT: We investigate the Delta S = 0 effective chiral Lagrangian from the instanton vacuum. Based on the Delta S = 0 effective weak Hamiltonian from the operator product expansion and renormalization group equations, we derive the strangeness-conserving effective weak chiral Lagrangian from the instanton vacuum to order {{mathcal{O}}}(p^2) and the next-to-leading order in the 1/ N c expansion at the quark level. We find that the quark condensate and a dynamical term which arise from the QCD and electroweak penguin operators appear in the next-to-leading order in the 1/ N c expansion for the Delta S = 0 effective weak chiral Lagrangian, while they are in the leading order terms in the Delta S = 1 case. Three different types of form factors are employed and we find that the dependence on the different choices of the form factor is rather insensitive. The low-energy constants of the Gasser-Leutwyler type are determined and discussed in the chiral limit.
    European Physical Journal C 01/2006; 45:451-457. · 5.25 Impact Factor
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    Hong-Jo Park, Chang-Hwan Lee, Gerald E. Brown
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    ABSTRACT: We discuss the problem of mass, noting that meson masses decrease with increasing scale as the dynamically generated condensate of “soft glue” is melted (Brown/Rho scaling). We then extend the Bielefeld LGS (Lattice Gauge Simulation) color-singlet interaction computed for heavy quarks in a model-dependent way by including the Ampére law velocity–velocity interaction. Parameterizing the resulting interaction in terms of effective strength of the potential and including screening, we find that the masses of π, σ, ρ and A1 excitations, 32 degrees of freedom in all, go to zero (in the chiral limit) as T→Tc essentially independently of the input quark (thermal) masses in the range of 1–2 GeV, calculated also in Bielefeld. We discuss other LGS which show bound states, which we interpret as our chirally restored mesons, for T>Tc.
    Nuclear Physics A 12/2005; · 2.50 Impact Factor
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    Chang-Hwan Lee, Gerald E. Brown
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    ABSTRACT: Double neutrons are especially important because they give most accurate informations on the masses of neutron stars. Observations on double neutron stars show that all masses of the neutron stars are below 1.5$\msun$. Furthermore, two neutron stars in a given double pulsar are nearly equal in mass. With hypercritical accretion, we found that the probability of having companion mass $>1.5\msun$ is larger than 90%, while there is no observations on such systems. We believe that those companions with masses higher than $1.5\msun$ went into black holes, which is consistent with our preferred maximum neutron star mass $M_{NS}^{max} \approx 1.5\msun$ due to the kaon condensation. In this work, we point out that the black-hole neutron star binaries are 10 times more dominant than double neutron star binaries. As a result, black-hole, neutron star binaries can increase the LIGO detection rate by a factor 20.
    11/2005;
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    Gerald E. Brown, Chang-Hwan Lee, Mannque Rho
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    ABSTRACT: We construct the nature of the matter found in RHIC when its temperature has dropped down close to, and below, $T_c$. Just above $T_c$ it is composed of extremely strongly bound quark-antiquark pairs forming chirally restored mesons of the quantum numbers of the $\pi, S, \rho$ and $a_1$ with very small size and zero energy and just below $T_c$, it is composed of mesons of the same quantum numbers with zero mass. We invoke infrared slavery for the former and the vector manifestation (VM) of hidden local symmetry for the latter. As the temperature drops below $T_c$, the strongly bound quark-antiquark pairs are ejected into what is basically a region of "hadronic freedom" in which the interactions are zero. Experimental evidences for this are seen in the STAR data.
    08/2005;
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    G. E. Brown, Chang-Hwan Lee, Mannque Rho
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    ABSTRACT: The hidden local symmetry effective theory, Wilsonian matched to QCD at a matching scale near the chiral scale $\sim 4\pi f_\pi$ as formulated by Harada and Yamawaki, presents a scenario drastically different from the standard scenario of heavy-ion collisions in that as the temperature approaches the critical temperature $T_c$ of chiral restoration from below, the mass of the vector mesons and their widths go to zero in the chiral limit or nearly zero otherwise, proportionally to some power of the quark condensate at what is called "vector manifestation (VM) fixed point". This scenario makes a striking prediction that as the fire-ball expands and cools from $T_c$ down toward the freezeout temperature $T_{freezeout}$ in heavy ion collisions, what we call "hadronic freedom" sets in in which hadrons do not interact or barely interact. We suggest that this scenario is testable at RHIC and as a specific example, we provide an astonishingly simple explanation in terms of the vector manifestation suitably extended to include axial-vector mesons for the anomalously large $\rho^0/\pi^-$ ratio measured in peripheral collisions by STAR. Comment: 4 pages, no figures
    07/2005;
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    Gerald E. Brown, Chang-Hwan Lee, Mannque Rho
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    ABSTRACT: Combining the recent experimental indications of density dependence in the pion decay constant $f_\pi^\star$ and the $\omega$ meson mass $m_\omega^\star$ and the discovery of $S^0 (3115)$ and other "strange nuggets" with the vector manifestation of chiral symmetry in hidden local symmetry proposed by Harada and Yamawaki, we show that the mechanism responsible for dense strangeness nuggets can be related to that responsible for kaon condensation in neutron-star matter. We suggest that this relation assures kaon condensation at a density $\sim$ three times nuclear matter density which supports the Brown-Bethe scenario for the $M_{\rm NS}^{max} \simeq 1.5\msun$. This low $M_{\rm NS}^{\rm max}\sim 1.5\msun$ has major consequences in astrophysics, especially for the merging rate of compact stellar objects.
    05/2005;
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    ABSTRACT: We consider the strangeness-conserving effective weak chiral Lagrangian based on the nonlocal chiral quark model from the instanton vacuum. We incorporate the effect of the strong interaction by the gluon into the effective Lagrangian. The effect of the Wilson coefficients on the weak pion-nucleon coupling constant is discussed briefly.
    12/2004: pages 105-105;
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    ABSTRACT: The main objective of this work is to explore the evolution in the structure of the quark-anti-quark bound states in going down in the chirally restored phase from the so-called ``zero binding points'' Tzb to the full (unquenched) QCD critical temperature Tc 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 c¯c, light-quark q¯q mesons π,σ,ρ,A1 and gluons that at Tzb, the quark-anti-quark scattering length goes through ∞ 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 Tzb all mesons are large-size nonrelativistic objects bound by Coulomb attraction, near Tc 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 Tc.
    Nuclear Physics A 07/2004; 740:171-194. · 2.50 Impact Factor
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    Gerald E. Brown, Chang-Hwan Lee, Mannque Rho
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    ABSTRACT: 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 A1 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⇆2π exhaust the interspecies transitions. We evaluate this reaction at Tc and find it to be much larger than below Tc, certainly strong enough to equilibrate the chirally restored mesons just above Tc. When emitted just below Tc the mesons remain in the Tc+ε freezeout distribution, 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 Tc 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 Tc) 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 Tc 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.
    Nuclear Physics A 05/2004; · 2.50 Impact Factor
  • Chang-Hwan Lee, Gerald E. Brown
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    ABSTRACT: We discuss the possibility that the soft X-ray transient GRS1915 + 105 evolved from a binary similar to V4641Sgr (XTEJ1819 - 254) by conservative mass-transfer, and estimate the possible mass-transfer rates during the evolution. The results indicate that the high mass-transfer rates could explain the high luminosities in ultraluminous X-ray sources. Although the high mass-transfer rates during evolution are accompanied by high luminosities, we find that much of the transferred matter may sweeps accompanying radiation in an adiabatic inflow of super-Eddington accretion. We suggest that soft X-ray transients with evolved companions (initial companion mass > 3 Modot), e.g. GRS 1915 + 105, can be ultraluminous X-ray sources if they are seen through their beaming axis.
    Publications- Astronomical Society of Japan 04/2004; · 2.44 Impact Factor
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    Gerald E. Brown, Chang-Hwan Lee, Mannque Rho
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    ABSTRACT: 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 $\pi, \sigma, \rho, A_1$ and gluons that at $T_{zb}$, the quark-antiquark scattering length goes through $\infty$ at which conformal invariance is restored, thereby transforming the matter into a near perfect fluid behaving hydrodynamically, as found at RHIC. We name this new state of matter as "sticky molasses". 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 $\sigma$ and $\pi$ 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 $T_c$.
    03/2004;
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    Hyun-Chul Kim, Chang-Hwan Lee, Hee-Jung Lee
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    ABSTRACT: We investigate medium modifications of the pentaquark $\Theta^+$ in dense medium, taking into account different parities of the exotic $\Theta^+$ baryon. We find that the chemical potential of the $\Theta^+$ is shifted in a density-dependent way to one-loop order. We also investigated the effect of the scaled nucleon mass in dense medium on the $\Theta^+$ propagator. The results turn out to depend sensitively on the scaled nucleon mass and on the parity of the $\Theta^+$.
    03/2004;
  • 01/2004;

Publication Stats

847 Citations
191.15 Total Impact Points

Institutions

  • 2014
    • West Virginia University
      • Department of Physics
      Morgantown, West Virginia, United States
  • 2003–2014
    • Pusan National University
      • Department of Physics
      Tsau-liang-hai, Busan, South Korea
  • 2008
    • SUNY Ulster
      Kingston, New York, United States
  • 2007
    • Cornell University
      Ithaca, New York, United States
  • 2006
    • State University of New York
      New York City, New York, United States
  • 1994–2001
    • Seoul National University
      • Center for Theoretical Physics
      Sŏul, Seoul, South Korea
  • 1996
    • University of Washington Seattle
      • Institute for Nuclear Theory
      Seattle, Washington, United States