20,122 research outputs found
Renormalization group approach to spinor Bose-Fermi mixtures in a shallow optical lattice
We study a mixture of ultracold spin-half fermionic and spin-one bosonic
atoms in a shallow optical lattice where the bosons are coupled to the fermions
via both density-density and spin-spin interactions. We consider the parameter
regime where the bosons are in a superfluid ground state, integrate them out,
and obtain an effective action for the fermions. We carry out a renormalization
group analysis of this effective fermionic action at low temperatures, show
that the presence of the spinor bosons may lead to a separation of Fermi
surfaces of the spin-up and spin-down fermions, and investigate the parameter
range where this phenomenon occurs. We also calculate the susceptibilities
corresponding to the possible superfluid instabilities of the fermions and
obtain their possible broken-symmetry ground states at low temperatures and
weak interactions.Comment: 8 pages, 8 figs v
Renormalization-group approach to superconductivity: from weak to strong electron-phonon coupling
We present the numerical solution of the renormalization group (RG) equations
derived in Ref. [1], for the problem of superconductivity in the presence of
both electron-electron and electron-phonon coupling at zero temperature. We
study the instability of a Fermi liquid to a superconductor and the RG flow of
the couplings in presence of retardation effects and the crossover from weak to
strong coupling. We show that our numerical results provide an ansatz for the
analytic solution of the problem in the asymptotic limits of weak and strong
coupling.Comment: 8 pages, 3 figures, conference proceedings for the Electron
Correlations and Materials Properties, in Kos, Greece, July 5-9, 200
Analyses of composite structures
Stiffness and strength analyses on composite cross-ply and helical wound cylinders and flat laminate structure
Optical probes of the quantum vacuum: The photon polarization tensor in external fields
The photon polarization tensor is the central building block of an effective
theory description of photon propagation in the quantum vacuum. It accounts for
the vacuum fluctuations of the underlying theory, and in the presence of
external electromagnetic fields, gives rise to such striking phenomena as
vacuum birefringence and dichroism. Standard approximations of the polarization
tensor are often restricted to on-the-light-cone dynamics in homogeneous
electromagnetic fields, and are limited to certain momentum regimes only. We
devise two different strategies to go beyond these limitations: First, we aim
at obtaining novel analytical insights into the photon polarization tensor for
homogeneous fields, while retaining its full momentum dependence. Second, we
employ wordline numerical methods to surpass the constant-field limit.Comment: 13 pages, 4 figures; typo in Eq. (5) corrected (matches journal
version
Weak dipole moment of in collisions with longitudinally polarized electrons
It is pointed out that certain CP-odd momentum correlations in the production
and subsequent decay of tau pairs in collisions get enhanced when the
is longitudinally polarized. Analytic expressions for these correlations
are obtained for the single-pion decay mode of when have
a ``weak" dipole form factor (WDFF) coupling to . For collisions
at the peak, a sensitivity of about 1-5\mbox{ cm} for
the WDFF can be reached using a {\em single} decay
channel, with 's likely to be available at the SLC at Stanford with
polarization of 62\%-75\%.Comment: 9 pages, Latex, PRL-TH-93/17 (Revised
Infrared probe of the anomalous magnetotransport of highly oriented pyrolytic graphite in the extreme quantum limit
We present a systematic investigation of the magnetoreflectance of highly
oriented pyrolytic graphite in magnetic field B up to 18 T . From these
measurements, we report the determination of lifetimes tau associated with the
lowest Landau levels in the quantum limit. We find a linear field dependence
for inverse lifetime 1/tau(B) of the lowest Landau levels, which is consistent
with the hypothesis of a three-dimensional (3D) to 1D crossover in an
anisotropic 3D metal in the quantum limit. This enigmatic result uncovers the
origin of the anomalous linear in-plane magnetoresistance observed both in bulk
graphite and recently in mesoscopic graphite samples
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