Browsing by Author "Yang, Di-Lun"

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Chiral Hall effect and chiral electric waves
(2015-01-14)
Pu, Shi
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Wu, Shang-Yu
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Yang, Di-Lun
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物理研究所
;
丘成桐中心
We investigate the vector and axial currents induced by external electromagnetic fields and chemical potentials in chiral systems at finite temperature. Similar to the normal Hall effect, we find that an axial Hall current is generated in the presence of the electromagnetic fields along with an axial chemical potential, which may be dubbed as the "chiral Hall effect" (CHE). The CHE is related to the interactions of chiral fermions and exists with a nonzero axial chemical potential. We argue that the CHE could lead to nontrivial charge distributions at different rapidity in asymmetric heavy ion collisions. Moreover, we study the chiral electric waves led by the fluctuations of the vector and axial chemical potentials along with the chiral electric separation effect, where a density wave propagates along the applied electric field. Combining with the normal/chiral Hall effects, the fluctuations of chemical potentials thus result in Hall density waves. The Hall density waves may survive even at zero chemical potentials and become nondissipative. We further study the transport coefficients including the Hall conductivities, damping times, wave velocities, and diffusion constants of chiral electric waves in a strongly coupled plasma via the AdS/CFT correspondence.
Elliptic flow from thermal photons with magnetic field in holography
(2014-01-28)
Mueller, Berndt
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Wu, Shang-Yu
;
Yang, Di-Lun
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物理研究所
;
丘成桐中心
We compute the elliptic flow v(2) of thermal photons in a strongly coupled plasma with constant magnetic field via gauge/gravity duality. The D3/D7 embedding is applied to generate the contributions from massive quarks. By considering the cases in 2 + 1 flavor super Yang-Mills analogous to the photon production in quark gluon plasma, we obtain the thermal photon v(2), which is qualitatively consistent with the direct photon v(2) measured at the relativistic heavy ion collider at intermediate energy. However, due to the simplified setup, the thermal photon v(2) in our model should be regarded as the upper bound for the v(2) generated by solely a magnetic field in the strongly coupled scenario.
Holographic chiral electric separation effect
(2014-04-10)
Pu, Shi
;
Wu, Shang-Yu
;
Yang, Di-Lun
;
物理研究所
;
丘成桐中心
We investigate the chiral electric separation effect, where an axial current is induced by an electric field in the presence of both vector and axial chemical potentials, in a strongly coupled plasma via the Sakai-Sugimoto model with a U(1)(R) x U(1)(L) symmetry. By introducing different chemical potentials in U(1)(R) and U(1)(L) sectors, we compute the axial direct current (DC) conductivity stemming from the chiral current and the normal DC conductivity. We find that the axial conductivity is approximately proportional to the product of the axial and vector chemical potentials for arbitrary magnitudes of the chemical potentials. We also evaluate the axial alternating current (AC) conductivity induced by a frequency-dependent electric field, where the oscillatory behavior with respect to the frequency is observed.
Holographic photon production with magnetic field in anisotropic plasmas
(2013-08-01)
Wu, Shang-Yu
;
Yang, Di-Lun
;
物理研究所
;
Institute of Physics
We investigate the thermal photon production from constant magnetic field in a strongly coupled and anisotropic plasma via the gauge/gravity duality. The dual geometry with pressure anisotropy is generated from the axion-dilaton gravity action introduced by Mateos and Trancancelli and the magnetic field is coupled to fundamental matters(quarks) through the D3/D7 embeddings. We find that the photon spectra with different quark mass are enhanced at large frequency when the photons are emitted parallel to the anisotropic direction with larger pressure or perpendicular to the magnetic field. However, in the opposite conditions for the emitted directions, the spectra approximately saturate isotropic results in the absence of magnetic field. On the other hand, a resonance emerges at moderate frequency for the photon spectrum with heavy quarks when the photons move perpendicular to the magnetic field. The resonance is more robust when the photons are polarized along the magnetic field. On the contrary, in the presence of pressure anisotropy, the resonance will be suppressed. There exist competing effects of magnetic field and pressure anisotropy on meson melting in the strongly coupled super Yang-Mills plasma, while we argue that the suppression led by anisotropy may not be applied to the quark gluon plasma.