119293360
Non-Fermi liquid behavior due to U(1) gauge field in two dimensions
Abstract We study the damping rate of massless Dirac fermions due to the U ( 1 ) gauge field in ( 2 + 1 ) -dimensional quantum electrodynamics. In the absence of a Maxwell term for the gauge field, the fermion damping rate Im Σ ( ω , T ) is found to diverge in both perturbative and self-consistent results. In the presence of a Maxwell term, there is still divergence in the perturbative results for Im Σ ( ω , T ) . Once the Maxwell term is included into the self-consistent equations for fermion self-energy and vacuum polarization functions, the fermion damping rate is free of divergence and exhibits non-Fermi liquid behavior: Im Σ ( ω , T ) ∝ max ( ω , T ) .
118466485
Nature of the antiferromagnetic quantum phase transition on the honeycomb lattice
We address the nature of the antiferromagnetic quantum phase transition that separates a semimetal from an antiferromagnet in the repulsive Hubbard model defined on the honeycomb lattice. At the critical point, the fermions acquire an anomalous dimension $\eta$ due to their strong coupling to the fluctuations of the order parameter $\phi$. The finite $\eta$ in turn induces a singular $\phi^{4}$ term and a non-analytical spin susceptibility signaling the breakdown of Hertz's $\phi^{4}$ theory. As a result, the continuous antiferromagnetic quantum phase transition is internally unstable and turns into a first order transition.
118643259
Fate of non-Fermi-liquid behavior in QED 3 at finite chemical potential
The damping rate of two-dimensional massless Dirac fermions exhibit non-Fermi-liquid behavior, {proportional_to}{epsilon}{sup 1/2}, due to gauge field at zero temperature and zero chemical potential. We study the fate of this behavior at finite chemical potential. We first calculate explicitly the temporal and spatial components of vacuum polarization functions. The analytical expressions imply that the temporal component of gauge field develops a static screening length at finite chemical potential while the transverse component remains long-ranged owing to gauge invariance. We then calculate the fermion damping rate and show that the temporal gauge field leads to normal Fermi-liquid behavior but the transverse gauge field leads to non-Fermi-liquid behavior {proportional_to}{epsilon}{sup 2/3} at zero temperature. This energy dependence is more regular than {proportional_to}{epsilon}{sup 1/2} and does not change as chemical potential varies.
119270094
Confinement induced by fermion damping in three-dimensional QED
The three-dimensional noncompact QED is known to exhibit weak confinement when fermions acquire a finite mass via the mechanism of dynamical chiral symmetry breaking. In this paper, we study the effect of fermion damping caused by elastic scattering on the classical potential between fermions. By calculating the vacuum polarization function that incorporates the fermion damping effect, we show that the fermion damping can induce a weak confinement even when the fermions are massless and the chiral symmetry is not broken.
123480931
EFFECTIVE COSMOLOGICAL CONSTANT IN BRANE COSMOLOGY
We consider a brane-world of co-dimension one without reflection symmetry. Through it, we give a possible explanation of the great discrepancy between the vacuum energy and the observed cosmological constant without contradiction to the knowledge we have about our Universe. We also show the gravity observed will be standard four-dimensional gravity as long as the discrepancy of the bulk cosmological constant at different sides of the brane is small enough.
119252933
Competition between excitonic gap generation and disorder scattering in graphene
We study the disorder effect on the excitonic gap generation caused by strong Coulomb interaction in graphene. By solving the self-consistently coupled equations of dynamical fermion gap m and disorder scattering rate Γ, we have found a critical line on the plane of interaction strength λ and disorder strength g. The phase diagram is divided into two regions: in the region with large λ and small g, m≠0 and Γ=0; in the other region, m=0 and Γ≠0 for nonzero g. In particular, there is no coexistence of finite fermion gap and finite scattering rate. These results imply a strong competition between excitonic gap generation and disorder scattering. This conclusion does not change when an additional contact four-fermion interaction is included. For sufficiently large λ, the growing disorder may drive a quantum phase transition from an excitonic insulator to a metal.
17439945
Units and numerical values of the effective couplings in perturbative heterotic string vacua
We determine the units and numerical values for a class of couplings in the effective theory of perturbative heterotic string vacua, with the emphasis on the correct translation between the canonical gauge coupling g and Planck scale M{sub Planck}{approximately}1.2{times}10{sup 19}GeV as used in the effective theory description and the string coupling g{sub string} and string tension {alpha}{sup {prime}} as used in the S-matrix amplitude calculation. In particular, we determine the effective couplings in the superpotential and reexamine the Fayet-Iliopoulos (FI) term in a class of models with an anomalous U(1). We derive the values of the effective Yukawa couplings (at the third and fourth order) after the restabilization of vacuum along a particular F- and D-flat direction and show that they are {ital comparable} in magnitude. The result corrects results quoted in the literature, and may have implications for the string derived phenomenology, e.g., that of fermion textures. {copyright} {ital 1999} {ital The American Physical Society}
118677286
Gamma-ray Burst Prompt Emission: Jitter Radiation in Stochastic Magnetic Field Revisited
We revisit the radiation mechanism of relativistic electrons in the stochastic magnetic field and apply it to the high-energy emissions of gamma-ray bursts (GRBs). We confirm that jitter radiation is a possible explanation for GRB prompt emission in the condition of a large electron deflection angle. In the turbulent scenario, the radiative spectral property of GRB prompt emission is decided by the kinetic energy spectrum of turbulence. The intensity of the random and small-scale magnetic field is determined by the viscous scale of the turbulent eddy. The microphysical parameters epsilon(e) and epsilon(B) can be obtained. The acceleration and cooling timescales are estimated as well. Due to particle acceleration in magnetized filamentary turbulence, the maximum energy released from the relativistic electrons can reach a value of about 10(14) eV. The GeV GRBs are possible sources of high-energy cosmic-ray.
119102309
Possible hard X-ray shortages in bursts from KS 1731-260 and 4U 1705-44
Aims. A hard X-ray shortage, implying the cooling of the corona, was observed during bursts of IGR J17473-272, 4U 1636-536, Aql X-1, and GS 1826-238. Apart from these four sources, we investigate here an atoll sample, in which the number of bursts for each source is larger than 5, to explore the possible additional hard X-ray shortage during Rossi X-ray timing explorer (RXTE) era. Methods. According to the source catalog that shows type-I bursts, we analyzed all the available pointing observations of these sources carried out by the RXTE proportional counter array. We grouped and combined the bursts according to their outburst states and searched for the possible hard X-ray shortage while bursting. Results. We found that the island states of KS 1731-260 and 4U 1705-44 show a hard X-ray shortage at significant levels of 4.5 and 4.7σ and a systematic time lag of 0.9 ± 2.1 s and 2.5 ± 2.0 s with respect to the soft X-rays, respectively. While in their banana branches and other sources, we did not find any consistent shortage.
118485758
Unveiling the super-orbital modulation of LS I +61 303 in X-rays
We found evidence for the super-orbital modulation in the X-ray emission of LS I +61 303 from the longest monitoring date by the RXTE. The time evolution of the modulated fraction in the orbital light curves can be well fitted with a sinusoidal function having a super-orbital period of 1667 days. However, we have found a 281.8+/-44.6 day shift between the super-orbital variability found at radio frequencies and our X-ray data. We also find a super-orbital modulation in the maximum count rate of the orbital light curves, compatible with the former results, including the shift.
121992643
The Wigner Functions for a Spin-1/2 Relativistic Particle in the Presence of Magnetic Field
This paper provides a study of Wigner functions for a spin-1/2 relativistic particle in the presence of magnetic field. Since the Dirac equation is described as a matrix equation, it is necessary to describe the Wigner function as a matrix function in phase space. What’s more, this function is then proved to satisfy the Dirac equation with ⋆-product. Finally, by solving the ⋆-product Dirac equation, the energy levels as well as the Wigner functions for a spin-1/2 relativistic particle in the presence of magnetic field are obtained.