arXiv subjects

Deog Ki Hong

Publications and source records attributed to Deog Ki Hong.

At least 109 records · Page 6Linked to original sources

arXiv2004

High Density Effective Theory of QCD

We discuss the salient features of the high density effective theory (HDET) of QCD, elaborating more on the matching for vector-vector correlators and axial-vector-vector correlators, which are related to screening mass and axial anomaly, respectively. We then apply HDET to discuss various color-superconducting phases of dense QCD. We also review a recent proposal to solve the sign problem in dense fermionic matter, using the positivity property of HDET. Positivity of HDET allows us to establish rigorous inequalities in QCD at asymptotic density and to show vector symmetry except the fermion number is not spontaneously broken at asymptotic density.

hep-ph↗

arXiv2003

Positivity and Fermionic Dense Matter

Euclidean dense matter generically suffers from the fermion sign problem. However, we argue that the sign problem is absent if one considers only low-energy degrees of freedom. Specifically, the low energy effective theory of dense QCD has positive Euclidean path integral measure, which allows one to establish rigorous inequalities showing that the color-flavor locked (CFL) phase is the true vacuum of three flavor, massless QCD. We then describe a method for simulating dense QCD on the lattice. We also discuss applications to electronic systems in condensed matter, such as generalized Hubbard models.

hep-lat↗

arXiv2003

Positivity and Dense Matter

We elaborate on previous results concerning the positivity of the Euclidean path integral measure for low-energy modes in dense fermionic matter. We show that the sign problem usually associated with fermions is absent if one considers only low-energy degrees of freedom. We describe a method for simulating dense QCD on the lattice and give a proof using rigorous inequalities that the color-flavor locked (CFL) phase is the true vacuum of three flavor, massless QCD. We also discuss applications to electronic systems in condensed matter, such as generalized Hubbard models.

hep-ph↗

arXiv2003

Higher order corrections to Color superconducting gaps

We find a (nonlocal) gauge where the wavefunction renormalization constant does not get any corrections for all momenta in the hard-dense loop approximation. In this gauge, we solve the Schwinger-Dyson equations for the diquark condensate in dense QCD to calculate the Cooper pair gap. We determine not only the exponent but also the prefactor of the gap in a gauge independent way. We find that the higher order corrections increase the gap only by about 1.6 times to the leading order gap at Coulomb gauge.

hep-ph↗

arXiv2003

High Temperature Superfluid and Feshbach Resonance

We study an effective field theory describing cold fermionic atoms near a Feshbach resonance. The theory gives a unique description of the dynamics in the limit that the energy of the Feshbach resonance is tuned to be twice that of the Fermi surface. We show that in this limit the zero temperature superfluid condensate is of order the Fermi energy, and obtain a critical temperature $T_C \simeq 0.43 T_F$

cond-mat↗

arXiv2003

Positivity of QCD at asymptotic density

In this talk, I try to show that the sign problem of dense QCD is due to modes whose frequency is higher than the chemical potential. An effective theory of quasi-quarks near the Fermi surface has a positive measure in the leading order. The higher-order corrections make the measure complex, but they are suppressed as long as the chemical potential is sufficiently larger than $Λ_{\rm QCD}$. As a consequence of the positivity of the effective theory, we can show that the global vector symmetries except the U(1) baryon number are unbroken at asymptotic density.

hep-ph↗

arXiv2002

Positivity of High Density Effective Theory

We show that the effective field theory of low energy modes in dense QCD has positive Euclidean path integral measure. The complexity of the measure of QCD at finite chemical potential can be ascribed to modes which are irrelevant to the dynamics at sufficiently high density. Rigorous inequalities follow at asymptotic density. Lattice simulation of dense QCD should be possible using the quark determinant calculated in the effective theory.

hep-ph↗

arXiv2001

Crystalline Color Superconductivity in Dense Matter

In this talk I discuss a recently proposed color superconducting phase of asymmetric quark matter where the up and down quark have different chemical potential, being in chemical equilibrium with electrons. Using Schwinger-Dyson equations derived from an effective theory of low-energy quasiparticles, a critical coupling for LOFF phase is estimated for both the case of an effective four Fermi interaction and Landau-damped one gluon exchange.

hep-ph↗

arXiv2001

Supernovae, Hypernovae and Color Superconductivity

We argue that Color Superconductivity (CSC, Cooper pairing in quark matter leading to the breaking of SU(3) color symmetry) may play a role in triggering the explosive endpoint of stellar evolution in massive stars (M > 8 M_{\odot}). We show that the binding energy release in the transition of a sub-core region to the CSC phase can be of the same order of magnitude as the gravitational binding energy release from core collapse. The core temperature during collapse is likely below the critical temperature for CSC, and the transition is first order, proceeding on Fermi timescales when the pressure reaches a critical value of several times nuclear density. We also discuss the implications for hypernova events with total ejecta energy of 10-100 times that of type II supernova.

hep-ph↗

arXiv2001

Critical couplings in Crystalline Color superconductivity

Solving the Schwinger-Dyson equations, we analyze the pairing of quarks in asymmetric quark matter where quarks have different chemical potentials. We show that in the asymmetric quark matter a crystalline color-superconducting gap opens when the quark coupling is stronger than a critical value. The critical coupling is nonzero, since the infrared divergence is lessened when the momenta of pairing quarks are not opposite. The superconducting gaps and the critical couplings are calculated both at high and intermediate densities.

hep-ph↗

arXiv2001

Aspects of Color Superconductivity

I discuss some aspects of recent developments in color superconductivity in high density quark matter. I calculate the Cooper pair gap and the critical points at high density, where magnetic gluons are not screened. The ground state of high density QCD with three light flavors is shown to be a color-flavor locking state, which can be mapped into the low-density hadronic phase. The meson mass at the CFL superconductor is also calculated. The CFL color superconductor is bosonized, where the Fermi sea is identified as a $Q$-matter and the gapped quarks as topological excitations, called superqualitons, of mesons. Finally, as an application of color supercoductivity, I discuss the neutrino interactions in the CFL color superconductor.

hep-ph↗

arXiv2000

Bosonization of QCD at high density

We describe the color-flavor locking (CFL) color superconductor in terms of bosonic variables, where the gaped quarks are realized as solitons, so-called superqualitons. We then show that the ground state of the CFL color superconductor is a $Q$-matter, which is the lowest energy state for a given fixed baryon number. From this $Q$-matter, we calculate the minimal energy to create a superqualiton and argue that it is twice of the Cooper gap. Upon quantizing the zero modes of superqualitons, we find superqualitons have the same quantum number as the gaped quarks and furthermore all the high spin states of superqualitons are absent in the effective bosonic description of the CFL color superconductor.

hep-ph↗

arXiv2000

Radiative mass in QCD at high density

We show that radiatively generated Majorana mass for antiquarks is same as the Cooper-pair gap. We then calculate the electromagnetic corrections to mass of particles in the color-flavor locking phase of QCD at high density. The mass spectrum forms multiplets under $SU(2)_V\times U(1)_V$. The charged pions and kaons get the electromagnetic mass which is proportional to the Cooper-pair gap.

hep-ph↗

arXiv2000

Color Superconductivity in High Density Effective Theory

In this talk, I discuss the recent development in color superconductivity in terms of effective field theory. By investigating the Cooper pair gap equations at high density, we see that the effective theory simplifies the gap analysis very much, especially in finding the ground state, the precise form of the gap, and the critical temperature. Furthermore, the effective theory enables us to estimate the critical density for color superconductivity, which is found to be around $230~{\rm MeV}$ in the hard-dense-loop approximation. Finally, I briefly mention the low-lying spectra of color superconductor at high density.

hep-ph↗

arXiv2000

Meson Mass at Large Baryon Chemical Potential in Dense QCD

We reexamine the quark mass induced term in chiral Lagrangian in color-flavor locking phase in dense QCD, and show that the meson mass term is determined by three independent invariants under chiral-axial symmetry, and a meson mass is given in terms of the quark mass, gap, and the chemical potential by $m_π^2\sim m_q^2Δ\barΔ/μ^2\ln(μ^2/Δ^2)$. Thus mesons become massless as $μ\to\infty$.

hep-ph↗

arXiv2000

Aspects of high density effective theory in QCD

We study an effective theory of QCD at high density in detail, including the finite temperature effects and the leading order correction in $1/μ$ expansion. We investigate the Cooper pair gap equation and find that the color-flavor locking phase is energetically preferred at high density. We also find the color-superconducting phase transition occurs in dense quark matter when the chemical potential is larger than $250\pm 100~{\rm MeV}$ and the temperature is lower than 0.57 times the Cooper pair gap in the leading order in the hard-dense-loop approximation. The quark-neutrino four-Fermi coupling and the quark-axion coupling receive significant corrections in dense quark matter.

hep-ph↗

arXiv1999

An effective field theory of QCD at high density

We derive a (Wilsonian) effective field theory of QCD at finite density by integrating out the states in the Dirac sea when the chemical potential $μ\ggΛ_{\rm QCD}$. The quark-gluon coupling is effectively (1+1)-dimensional and the theory contains four-quark operators which become relevant as we approach to the Fermi sea. By calculating the one-loop vacuum polarization tensor in the effective theory, we find the electric gluons have a screening mass, $M\sim g_sμ$, while the static magnetic gluons are unscreened. We then investigate the gap equations for color anti-triplet Cooper pairs by including both gluon-exchange interactions and the marginal four-quark interactions in the effective theory.

hep-ph↗

arXiv1999

Qualitons At High Density

In the color-flavor-locked (CFL) phase of the QCD superconductor we show that baryons behave as qualitons (called "superqualitons") with quantum numbers $B=(1 {\rm mod} 2)/3$, S=1/2 and Y=B. An intriguing possibility implied by this identification is that light baryonic modes in the form of superqualitons could be excited below the (color) superconducting gap in the CFL phase, a novel phenomenon foreign to normal superconductors.

hep-ph↗