6,909 research outputs found
Spinon-Holon binding in model
Using a phenomenological model, we discuss the consequences of spinon-holon
binding in the U(1) slave-boson approach to model. Within a small
( hole concentration) expansion, we show that spinon-holon binding produces
a pseudo-gap normal state with a segmented Fermi surface and the
superconducting state is formed by opening an "additional" d-wave gap on the
segmented Fermi surface. The d-wave gap merge with the pseudo-gap smoothly as
temperature . The quasi-particles in the superconducting state are
coupled to external electromagnetic field with a coupling constant of order
where , depending on the strength of the
effective spinon-holon binding potential.Comment: 9 pages, 3 figure
Nearly Degenerate Gauginos and Dark Matter at the LHC
Motivated by dark-matter considerations in supersymmetric theories, we
investigate in a fairly model-independent way the detection at the LHC of
nearly degenerate gauginos with mass differences between a few GeV and about 30
GeV. Due to the degeneracy of gaugino states, the conventional leptonic signals
are likely lost. We first consider the leading signal from gluino production
and decay. We find that it is quite conceivable to reach a large statistical
significance for the multi-jet plus missing energy signal with an integrated
luminosity about 50 pb^-1 (50 fb^-1) for a gluino mass of 500 GeV (1 TeV). If
gluinos are not too heavy, less than about 1.5 TeV, this channel can typically
probe gaugino masses up to about 100 GeV below the gluino mass. We then study
the Drell-Yan type of gaugino pair production in association with a hard QCD
jet, for gaugino masses in the range of 100-150 GeV. The signal observation may
be statistically feasible with about 10 fb^-1, but systematically challenging
due to the lack of distinctive features for the signal distributions. By
exploiting gaugino pair production through weak boson fusion, signals of large
missing energy plus two forward-backward jets may be observable at a 4-6\sigma
level above the large SM backgrounds with an integrated luminosity of 100-300
fb^-1. Finally, we point out that searching for additional isolated soft muons
in the range p_T ~3-10 GeV in the data samples discussed above may help to
enrich the signal and to control the systematics. Significant efforts are made
to explore the connection between the signal kinematics and the relevant masses
for the gluino and gauginos, to probe the mass scales of the superpartners, in
particular the LSP dark matter.Comment: 35 pages, 32 figure
Reversal-Field Memory in the Hysteresis of Spin Glasses
We report a novel singularity in the hysteresis of spin glasses, the
reversal-field memory effect, which creates a non-analyticity in the
magnetization curves at a particular point related to the history of the
sample. The origin of the effect is due to the existence of a macroscopic
number of "symmetric clusters" of spins associated with a local spin-reversal
symmetry of the Hamiltonian. We use First Order Reversal Curve (FORC) diagrams
to characterize the effect and compare to experimental results on thin magnetic
films. We contrast our results on spin glasses to random magnets and show that
the FORC technique is an effective "magnetic fingerprinting" tool.Comment: 4 pages, 6 figure
Reversal-field memory in magnetic hysteresis
We report results demonstrating a singularity in the hysteresis of magnetic
materials, the reversal-field memory effect. This effect creates a
nonanalyticity in the magnetization curves at a particular point related to the
history of the sample. The microscopic origin of the effect is associated with
a local spin-reversal symmetry of the underlying Hamiltonian. We show that the
presence or absence of reversal-field memory distinguishes two widely studied
models of spin glasses (random magnets).Comment: 3 pages, 5 figures. Proceedings of "2002 MMM Conferece", Tampa, F
On the realization of Symmetries in Quantum Mechanics
The aim of this paper is to give a simple, geometric proof of Wigner's
theorem on the realization of symmetries in quantum mechanics that clarifies
its relation to projective geometry. Although several proofs exist already, it
seems that the relevance of Wigner's theorem is not fully appreciated in
general. It is Wigner's theorem which allows the use of linear realizations of
symmetries and therefore guarantees that, in the end, quantum theory stays a
linear theory. In the present paper, we take a strictly geometrical point of
view in order to prove this theorem. It becomes apparent that Wigner's theorem
is nothing else but a corollary of the fundamental theorem of projective
geometry. In this sense, the proof presented here is simple, transparent and
therefore accessible even to elementary treatments in quantum mechanics.Comment: 8 page
Fermi-edge problem in the presence of AC electric field
We study in this paper a non-equilibrium Fermi-edge problem where the system
under investigation is a single electron reservoir putting under an AC electric
field. We show that the electron Green's function and other correlation
functions in the problem can be solved and expressed exactly in terms of a
well-defined integral. The qualitative behaviors of the solution is studied and
compared with the situation where the impurity is coupled to more than one
reservoirs at different chemical potentials.Comment: Published versio
No Second Chance to Make a First Impression: The “Thin‐Slice” Effect on Instructor Ratings and Learning Outcomes in Higher Education
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134071/1/jedm12116_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134071/2/jedm12116.pd
Excitations in one-dimensional S=1/2 quantum antiferromagnets
The transition from dimerized to uniform phases is studied in terms of
spectral weights for spin chains using continuous unitary transformations
(CUTs). The spectral weights in the S=1 channel are computed perturbatively
around the limit of strong dimerization. We find that the spectral weight is
concentrated mainly in the subspaces with a small number of elementary triplets
(triplons), even for vanishing dimerization. So, besides spinons, triplons may
be used as elementary excitations in spin chains. We conclude that there is no
necessity to use fractional excitations in low-dimensional, undoped or doped
quantum antiferromagnets.Comment: 4 pages, 1 figure include
Low energy physical properties of high-Tc superconducting Cu oxides: A comparison between the resonating valence bond and experiments
In a recent review by Anderson and coworkers\cite{Vanilla}, it was pointed
out that an early resonating valence bond (RVB) theory is able to explain a
number of unusual properties of high temperature superconducting (SC)
Cu-oxides. Here we extend previous calculations \cite{anderson87,FC
Zhang,Randeria} to study more systematically low energy physical properties of
the plain vanilla d-wave RVB state, and to compare results with the available
experiments. We use a renormalized mean field theory combined with variational
Monte Carlo and power Lanczos methods to study the RVB state of an extended
model in a square lattice with parameters suitable for the hole doped
Cu-oxides. The physical observable quantities we study include the specific
heat, the linear residual thermal conductivity, the in-plane magnetic
penetration depth, the quasiparticle energy at the antinode , the
superconducting energy gap, the quasiparticle spectra and the Drude weight. The
traits of nodes (including , the Fermi velocity and the velocity
along Fermi surface ), as well as the SC order parameter are also
studied. Comparisons of the theory and the experiments in cuprates show an
overall qualitative agreement, especially on their doping dependences.Comment: 12 pages, 14 figures, 1 tabl
Photon-Photon Luminosities in Relativistic Heavy Ion Collisions at LHC Energies
Effective photon-photon luminosities are calculated for various realistic
hadron collider scenarios. The main characteristics of photon-photon processes
at relativistic heavy-ion colliders are established and compared to the
corresponding photon-photon luminosities at electron-positron and future Photon
Linear Colliders (PLC). Higher order corrections as well as inelastic processes
are discussed. It is concluded that feasible high luminosity Ca-Ca collisions
at the Large Hadron Collider (LHC) are an interesting option for photon-photon
physics up to about 100 GeV photon-photon CM energy.Comment: REVTeX, 13 pages, 10 figures (uuencoded,compressed postscript
- …