4,442 research outputs found
Remnant superfluid collective phase oscillations in the normal state of systems with resonant pairing
The signature of superfluidity in bosonic systems is a sound wave-like
spectrum of the single particle excitations which in the case of strong
interactions is roughly temperature independent. In fermionic systems, where
fermion pairing arises as a resonance phenomenon between free fermions and
paired fermionic states (examples are: the atomic gases of lithium or potassium
controlled by a Feshbach resonance, polaronic systems in the intermediary
coupling regime, d-wave hole pairing in the strongly correlated Hubbard
system), remnants of such superfluid characteristics are expected to be visible
in the normal state. The single particle excitations maintain there a sound
wave like structure for wave vectors above a certain q_{min}(T) where they
practically coincide there with the spectrum of the superfluid phase for
T<T_{c}. Upon approaching the transition from above this region in q-space
extends down to small momenta, except for a narrow region around q=0 where such
modes change into damped free particleComment: 5 pages, 3 figures; to appear in Phys Rev
Possible Phases of the Two-Dimensional t-t' Hubbard Model
We present a stability analysis of the 2D t-t' Hubbard model on a square
lattice for various values of the next-nearest-neighbor hopping t' and electron
concentration. Using the free energy expression, derived by means of the flow
equations method, we have performed numerical calculation for the various
representations under the point group C_{4\nu} in order to determine at which
temperature symmetry broken phases become more favorable than the symmetric
phase. A surprisingly large number of phases has been observed. Some of them
have an order parameter with many nodes in k-space. Commonly discussed types of
order found by us are antiferromagnetism, d_{x^2-y^2}-wave singlet
superconductivity, d-wave Pomeranchuk instability and flux phase. A few
instabilities newly observed are a triplet analog of the flux phase, a
particle-hole instability of p-type symmetry in the triplet channel which gives
rise to a phase of magnetic currents, an s*-magnetic phase, a g-wave
Pomeranchuk instability and the band splitting phase with p-wave character.
Other weaker instabilities are found also. A comparison with experiments is
made.Comment: revised version according to the referee remark
Flow Equations and Normal Ordering
In this paper we consider flow-equations where we allow a normal ordering
which is adjusted to the one-particle energy of the Hamiltonian. We show that
this flow converges nearly always to the stable phase. Starting out from the
symmetric Hamiltonian and symmetry-broken normal ordering nearly always yields
symmetry breaking below the critical temperature.Comment: 7 page
Momentum space evolution of chiral three-nucleon forces
A framework to evolve three-nucleon (3N) forces in a plane-wave basis with
the Similarity Renormalization Group (SRG) is presented and applied to
consistent interactions derived from chiral effective field theory at
next-to-next-to-leading order (NLO). We demonstrate the unitarity of the
SRG transformation, show the decoupling of low and high momenta, and present
the first investigation of universality in chiral 3N forces at low resolution
scales. The momentum-space-evolved 3N forces are consistent and can be directly
combined with the standard SRG-evolved two-nucleon (NN) interactions for
ab-initio calculations of nuclear structure and reactions.Comment: 5 pages, 4 figure
Bogoliubov shadow bands in the normal state of superconducting systems with strong pair fluctuations
On the basis of a scenario where electron pairing is induced by resonant
two-particle scattering (the Boson Fermion model), we show how precursors of
the superconducting state - in form of overdamped Bogoliubov modes - emerge in
the normal state upon approaching the transition temperature from above. This
result is obtained by a renormalization technique based on continuous unitary
transformations (the flow equations), projecting out the coherent contributions
in the electron spectral function from an incoherent background.Comment: 4 pages, 2 figure
Finite-Size Scaling Exponents of the Lipkin-Meshkov-Glick Model
We study the ground state properties of the critical Lipkin-Meshkov-Glick
model. Using the Holstein-Primakoff boson representation, and the continuous
unitary transformation technique, we compute explicitly the finite-size scaling
exponents for the energy gap, the ground state energy, the magnetization, and
the spin-spin correlation functions. Finally, we discuss the behavior of the
two-spin entanglement in the vicinity of the phase transition.Comment: 4 pages, published versio
Similarity Renormalization Group for Few-Body Systems
Internucleon interactions evolved via flow equations yield soft potentials
that lead to rapid variational convergence in few-body systems.Comment: 3 pages, 6 figures. To appear in the proceedings of the 20th European
Conference on Few-Body Problems in Physics (EFB20), Pisa, September 10-14,
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The genomics of neonatal abstinence syndrome
Significant variability has been observed in the development and severity of neonatal abstinence syndrome (NAS) among neonates exposed to prenatal opioids. Since maternal opioid dose does not appear to correlate directly with neonatal outcome, maternal, placental, and fetal genomic variants may play important roles in NAS. Previous studies in small cohorts have demonstrated associations of variants in maternal and infant genes that encode the μ-opioid receptor (OPRM1), catechol-O-methyltransferase (COMT), and prepronociceptin (PNOC) with a shorter length of hospital stay and less need for treatment in neonates exposed to opioids in utero. Consistently falling genomic sequencing costs and computational approaches to predict variant function will permit unbiased discovery of genomic variants and gene pathways associated with differences in maternal and fetal opioid pharmacokinetics and pharmacodynamics and with placental opioid transport and metabolism. Discovery of pathogenic variants should permit better delineation of the risk of developing more severe forms of NAS. This review provides a summary of the current role of genomic factors in the development of NAS and suggests strategies for further genomic discovery
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