1,044 research outputs found
Tricritical Point in Quantum Phase Transitions of the Coleman-Weinberg Model at Higgs Mass
The tricritical point, which separates first and second order phase
transitions in three-dimensional superconductors, is studied in the
four-dimensional Coleman-Weinberg model, and the similarities as well as the
differences with respect to the three-dimensional result are exhibited. The
position of the tricritical point in the Coleman-Weinberg model is derived and
found to be in agreement with the Thomas-Fermi approximation in the
three-dimensional Ginzburg-Landau theory. From this we deduce a special role of
the tricritical point for the Standard Model Higgs sector in the scope of the
latest experimental results, which suggests the unexpected relevance of
tricritical behavior in the electroweak interactions.Comment: 5 pages, 1 figure, published in Phys. Lett.
Reentrant Phenomenon in Quantum Phase Diagram of Optical Boson Lattice
We calculate the location of the quantum phase transitions of a bose gas
trapped in an optical lattice as a function of effective scattering length
a_{\eff} and temperature . Knowledge of recent high-loop results on the
shift of the critical temperature at weak couplings is used to locate a {\em
nose} in the phase diagram above the free Bose-Einstein critical temperature
, thus predicting the existence of a reentrant transition {\em
above} , where a condensate should form when {\em increasing}
a_{\eff}. At zero temperature, the transition to the normal phase produces
the experimentally observed Mott insulator.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.htm
Analytical study of level crossings in the Stark-Zeeman spectrum of ground state OH
The ground electronic, vibrational and rotational state of the OH molecule is
currently of interest as it can be manipulated by electric and magnetic fields
for experimental studies in ultracold chemistry and quantum degeneracy. Based
on our recent exact solution of the corresponding effective Stark-Zeeman
Hamiltonian, we present an analytical study of the crossings and avoided
crossings in the spectrum. These features are relevant to non-adiabatic
transitions, conical intersections and Berry phases. Specifically, for an
avoided crossing employed in the evaporative cooling of OH, we compare our
exact results to those derived earlier from perturbation theory.Comment: 5 figures, to be published in Eur. Phys. J.
Recursive Graphical Construction of Feynman Diagrams in phi^4 Theory: Asymmetric Case and Effective Energy
The free energy of a multi-component scalar field theory is considered as a
functional W[G,J] of the free correlation function G and an external current J.
It obeys non-linear functional differential equations which are turned into
recursion relations for the connected Greens functions in a loop expansion.
These relations amount to a simple proof that W[G,J] generates only connected
graphs and can be used to find all such graphs with their combinatoric weights.
A Legendre transformation with respect to the external current converts the
functional differential equations for the free energy into those for the
effective energy Gamma[G,Phi], which is considered as a functional of the free
correlation function G and the field expectation Phi. These equations are
turned into recursion relations for the one-particle irreducible Greens
functions. These relations amount to a simple proof that Gamma[G,J] generates
only one-particle irreducible graphs and can be used to find all such graphs
with their combinatoric weights. The techniques used also allow for a
systematic investigation into resummations of classes of graphs. Examples are
given for resumming one-loop and multi-loop tadpoles, both through all orders
of perturbation theory. Since the functional differential equations derived are
non-perturbative, they constitute also a convenient starting point for other
expansions than those in numbers of loops or powers of coupling constants. We
work with general interactions through four powers in the field.Comment: 34 pages; abstract expanded; section IV.E about absorption of
tadpoles and one related reference added; eqs. (20) and (23) corrected;
further references added; some minor beautifications; to be published by
Phys.Rev.
Manufacturing a thin wire electrostatic trap (TWIST) for ultracold polar molecules
We present a detailed description on how to build a Thin WIre electroStatic
Trap (TWIST) for ultracold polar molecules. It is the first design of an
electrostatic trap that can be superimposed directly onto a magneto optical
trap (MOT). We can thus continuously produce ultracold polar molecules via
photoassociation from a two species MOT and instantaneously trap them in the
TWIST without the need for complex transfer schemes. Despite the spatial
overlap of the TWIST and the MOT, the two traps can be operated and optimized
completely independently due to the complementary nature of the utilized
trapping mechanisms.Comment: 5 pages, 8 figures, updated conten
Gapless Hartree-Fock-Bogoliubov Approximation for Bose Gases
A dilute Bose system with Bose-Einstein condensate is considered. It is shown
that the Hartree-Fock-Bogolubov approximation can be made both conserving as
well as gapless. This is achieved by taking into account all physical
normalization conditions, that is, the normalization condition for the
condensed particles and that for the total number of particles. Two Lagrange
multipliers, introduced for preserving these normalization conditions, make the
consideration completely self-consistent.Comment: Latex file, 22 pages, 2 figure
The quantum smectic as a dislocation Higgs phase
The theory describing quantum-smectics in 2+1 dimensions, based on
topological quantum melting is presented. This is governed by a dislocation
condensate characterized by an ordering of Burger's vector and this `dual shear
superconductor' manifests itself in the form of a novel spectrum of phonon-like
modes.Comment: 5 pages, 3 figures; minor changes in the tex
Gauge-invariant critical exponents for the Ginzburg-Landau model
The critical behavior of the Ginzburg-Landau model is described in a
manifestly gauge-invariant manner. The gauge-invariant correlation-function
exponent is computed to first order in the and -expansion, and found
to agree with the ordinary exponent obtained in the covariant gauge, with the
parameter in the gauge-fixing term .Comment: 4 pages, no figure
Trapping of ultracold polar molecules with a Thin Wire Electrostatic Trap
We describe the realization of a dc electric-field trap for ultracold polar
molecules, the thin-wire electrostatic trap (TWIST). The thin wires that form
the electrodes of the TWIST allow us to superimpose the trap onto a
magneto-optical trap (MOT). In our experiment, ultracold polar NaCs molecules
in their electronic ground state are created in the MOT via photoassociation,
achieving a continuous accumulation in the TWIST of molecules in low-field
seeking states. Initial measurements show that the TWIST trap lifetime is
limited only by the background pressure in the chamber.Comment: 4 pages, 3 figure
Diagrammatic calculation of energy spectrum of quantum impurity in degenerate Bose-Einstein condensate
In this paper we considered a quantum particle moving through delute
Bose-Einstein condensate at zero temperature. In our formulation the impurity
particle interacts with the gas of uncoupled Bogoliubov's excitations. We
constructed the perturbation theory for the Green's function of the impurity
particle with respect to the impurity-condensate interaction employing the
coherent-state path integral approach. The perturbative expansion for the
Green's function is resumed into the expansion for its poles with the help of
the diagrammatic technique developed in this work. The dispersion relation for
the impurity clothed by condensate excitations is obtained and effective mass
is evaluated beyond the Golden rule approximation
- …