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.
21963024
Eliashberg theory of excitonic insulating transition in graphene.
A sufficiently strong Coulomb interaction may open an excitonic fermion gap and thus drive a semi-metal-insulator transition in graphene. In this paper, we study the Eliashberg theory of excitonic transition by coupling the fermion gap equation self-consistently to the equation of the vacuum polarization function. Including the fermion gap into the polarization function increases the effective strength of the Coulomb interaction because it reduces the screening effects due to the collective particle-hole excitations. Although this procedure does not change the critical point, it leads to a significant enhancement of the dynamical fermion gap in the excitonic insulating phase. The validity of the Eliashberg theory is justified by showing that the vertex corrections are suppressed at the large N limit.
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.
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.
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.
118450700
Absence of dynamical gap generation in suspended graphene
There is an interesting proposal that the long-range Coulomb interaction in suspended graphene can generate a dynamical gap, which leads to a semimetal–insulator phase transition. We revisit this problem by solving the self-consistent Dyson–Schwinger equations of wave function renormalization and fermion gap. In order to satisfy the Ward identity, a suitable vertex function is introduced. The impact of singular velocity renormalization and that of dynamical screening on gap generation are both included in this formalism, and prove to be very important. We obtain a critical interaction strength, 3.2 < αc < 3.3, which is larger than the physical value α = 2.16 for suspended graphene. It therefore turns out that suspended graphene is a semimetal, rather than an insulator, at zero temperature.
11765644
A dynamo model for axisymmetric and non-axisymmetric solar magnetic fields
More and more observations are showing a relatively weak, but persistent, non-axisymmetric magnetic field co-existing with the dominant axisymmetric field on the Sun. Its existence indicates that the non-axisymmetric magnetic field plays an important role in the origin of solar activity. A linear non-axisymmetric α 2 ‐ � dynamo model is derived to explore the characteristics of the axisymmetric (m = 0) and the first non-axisymmetric (m = 1) modes and to provide a theoretical basis with which to explain the ‘active longitude’, ‘flip-flop’ and other non-axisymmetric phenomena. The model consists of an updated solar internal differential rotation, a turbulent diffusivity varying with depth, and an α-effect working at the tachocline in a rotating spherical system. The difference between the α 2 ‐� and the α‐� models and
16294383
Gravity in a box
We consider a brane-world construction which incorporates a finite region of flat space, ``the box'', surrounded by a region of anti-de Sitter space. This hybrid construction provides a framework which interpolates between the scenario proposed by Arkani-Hamed, Dimopoulos and Dvali, and that proposed by Randall and Sundrum. Within this composite framework, we investigate the effects of resonant modes on four-dimensional gravity. We also show that, on a probe brane in the anti-de Sitter region, there is enhanced production of on-shell nonresonant modes. We compare our model to some recent attempts to incorporate the Randall-Sundrum scenario into superstring theory.
119741336
Electron cloud instability studies in the Beijing Electron Positron Collider
The electron cloud instability (ECI) in the Beijing Electron Positron Collider (BEPC) was studied systematically with experiments and simulations in recent years. Several electron cloud detectors have been installed into the BEPC storage ring to measure the electron yield. The effects of solenoid, the clearing electrode, the chromaticity, and the octupole on ECI have been investigated in BEPC experimentally. To evaluate the ECI in BEPCII, the upgrade project of BEPC, a computer code has been developed to simulate the electron density in the antechamber under different conditions, as well as the progress of the single bunch and coupled-bunch instabilities caused by the electron cloud. The experimental and simulation results, as well as the activities, are reported in this paper.
36795205
Observation of chi(c2) production in B meson decay.
We report the first observation of chi(c2) production in B meson decays. We find an inclusive B-->chi(c2)X branching fraction of (1.80(+0.23)(-0.28)+/-0.26) x 10(-3). The data set, collected with the Belle detector at the KEKB e(+)e(-) collider, consists of 31.9 x 10(6) BB events. We also present branching fractions and momentum spectra for both chi(c1) and chi(c2) production.
15099712
Dark energy model with spinor matter and its quintom scenario
A class of dynamical dark energy models, dubbed spinor quintom, can be constructed by a spinor field psi with a nontraditional potential. We find that, if choosing suitable potential, this model is able to allow the equation-of-state to cross the cosmological constant boundary without introducing any ghost fields. In a further investigation, we show that this model is able to mimic a perfect fluid of Chaplygin gas with p = -c/rho during the evolution, and also realizes the quintom scenario with its equation-of-state across -1.