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Investigating limitations of the Hard Thermal Loop (HTL) approximation method in quantum field theory and its impact on dispersion relations. Comparison with complete loop calculations reveals information loss and altered screening potentials. Discusses implications for physical properties such as dynamical screening, oscillatory potentials, and RDFs in different states of matter.
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What does HTL lose? Hui Liu Jinan University, China
HTL approximation • Hard thermal loop (HTL) • Widely used approximation to self-energy • Advantages • Simple and convenient for further calculations • Gauge invariant • Restrictions • Requires weak coupling • Equivalent to high temperature approximation
Lattice result, hep-lat/0011006v1 Why not HTL • Some facts in RHIC experiment STAR collaboration, PRL 89 (2002) 132301 • Strongly coupled? Does HTL still work? • What information does HTL approximation lose compared to the complete loop?
Dispersion Relations • Dispersion relation • Fundamental property of a many-body system • Energy-momentum relation determined by the pole of effective propagator. ΠL: longitudinal component of self-energy ΠT: transverse component Equation of dispersion
Comparison • Self-energy of toy model QED • HTL • Complete one loop (C1L)
HTL C1L • Dispersion relations • Solve the equation of dispersion and find out the relation between ω and q q=iqi Above the plasma frequency, q is real and qi=0. While below it, q is complex. We plot ω-qi relation in the left area. The main difference between the two curves is the appearance of a threshold frequency on the C1L curve.
Dynamical screening • Dynamical screening regime • Below the plasma frequency, the modes are complex, which can be signaled by the screening of external charges . q=qr+iqi Above , is consis- tent zero. While below it has values, which indicates an expectant change in physics pro-perties.
Oscillatory potential • Static limit • HTL: Purely imaginary modes • C1L: Complex modes • Static screening potential —Debye screening —Oscillatory screening ~~~~~~~~~~~~~~ where
solid liquid gas Radial Distribution Function • RDF • Probability of finding two particles at a distance r • Density-density autocorrelation function • Typical RDFs of different states of matter
RDF of a liquid? • Which potential can result in a liquid? • RDF and the potential of “mean force” • Short range order • Indicate a liquid state? Molecular dynamical simulation Gelman, Shuryak, and Zahed, PRC 74, 044908 (06)
Conclusion • Physics concealed in the C1L dispersion relation might not be revealed by the HTL • Comparing the dispersion relations we found the existence of a threshold frequency in the dynamical screening regime of the C1L • Below the threshold frequency the modes contain both real and imaginary parts • In the static limit, the complex mode leads to an oscillatory screening potential, which is contrast to the Debye-like potential in the HTL case • The oscillatory potential could result in a liquid-like RDF, which might indicate the liquid QGP
RDF in hot QGP • Gluon polarization • RDF of QGP • Short range order. Very similar to the typical shape of liquid. Footprint of liquid QGP!? • Enhanced oscillations at lower temperatures
Non-zero frequencies • Frequency-dependent screening • For HTL, the potential is always Debye-like in the whole range of frequencies below the plasma frequency. • For C1L, the potential can be either Debye-like or oscillatory. • Above the threshold frequency the screening potential is Debye-like • below that frequency, the potential is oscillating.
Screening of a moving particle? • Current-current correlation • Static case – density correlation • Static screening potential • Non-static case • Frequency dependent screening potential