37,723 research outputs found
Phases of the infinite U Hubbard model
We apply the density matrix renormalization group (DMRG) to study the phase
diagram of the infinite U Hubbard model on 2-, 4-, and 6-leg ladders. Where the
results are largely insensitive to the ladder width, we consider the results
representative of the 2D square lattice model. We find a fully polarized
ferromagnetic Fermi liquid phase when n, the density of electrons per site, is
in the range 1>n>n_F ~ 4/5. For n=3/4 we find an unexpected commensurate
insulating "checkerboard" phase with coexisting bond density order with 4 sites
per unit cell and block spin antiferromagnetic order with 8 sites per unit
cell. For 3/4 > n, the wider ladders have unpolarized groundstates, which is
suggestive that the same is true in 2D
Two-player quantum pseudo-telepathy based on recent all-versus-nothing violations of local realism
We introduce two two-player quantum pseudo-telepathy games based on two
recently proposed all-versus-nothing (AVN) proofs of Bell's theorem [A.
Cabello, Phys. Rev. Lett. 95, 210401 (2005); Phys. Rev. A 72, 050101(R)
(2005)]. These games prove that Broadbent and Methot's claim that these AVN
proofs do not rule out local-hidden-variable theories in which it is possible
to exchange unlimited information inside the same light-cone (quant-ph/0511047)
is incorrect.Comment: REVTeX4, 5 page
A New Experiment to Study Hyperon CP Violation and the Charmonium System
Fermilab operates the world's most intense antiproton source, now exclusively
dedicated to serving the needs of the Tevatron Collider. The anticipated 2009
shutdown of the Tevatron presents the opportunity for a world-leading low- and
medium-energy antiproton program. We summarize the status of the Fermilab
antiproton facility and review physics topics for which a future experiment
could make the world's best measurements.Comment: 16 pages, 3 figures, to appear in Proceedings of CTP symposium on
Supersymmetry at LHC: Theoretical and Experimental Perspectives, The British
University in Egypt, Cairo, Egypt, 11-14 March 200
Fos co-operation with PTEN loss elicits keratoacanthoma not carcinoma due to p53/p21<sup>WAF</sup>-induced differentiation triggered by GSK3b inactivation and reduced AKT activity
To investigate gene synergism in multistage skin carcinogenesis, the RU486-inducible cre/lox system was employed to ablate PTEN function [K14.cre/D5PTENflx] in mouse epidermis expressing activated v-fos [HK1.fos]. RU486-treated HK1.fos/D5PTENflx mice exhibited hyperplasia, hyperkeratosis and tumours that progressed to highly differentiated keratoacanthomas rather than carcinomas, due to re-expression of high p53 and p21WAF levels. Despite elevated MAP kinase activity, cyclin D1/E2 over expression and increased AKT activity forming areas of highly proliferative, papillomatous keratinocytes, increasing levels of GSK3b inactivation exceeded a threshold that induced p53/p21WAF expression to halt proliferation and accelerate differentiation, giving the hallmark keratosis of keratoacanthomas. A pivotal facet to this GSK3b-triggered mechanism centred on increasing p53 expression in basal layer keratinocytes. This reduced activated AKT expression and released inhibition of p21WAF, which accelerated keratinocyte differentiation, as indicated by unique basal layer expression of differentiation-specific keratin K1, alongside premature filaggrin and loricrin expression. Thus, fos synergism with PTEN loss elicited a benign tumour context where GSK3b-induced, p53/p21WAF expression continually switched AKT-associated proliferation into one of differentiation, preventing further progression. This putative compensatory mechanism required the critical availability of normal p53 and/or p21WAF otherwise deregulated fos, Akt and GSK3b associate with malignant progression
A model of rotating hotspots for 3:2 frequency ratio of HFQPOs in black hole X-ray binaries
We propose a model to explain a puzzling 3:2 frequency ratio of high
frequency quasi-periodic oscillations (HFQPOs) in black hole (BH) X-ray
binaries, GRO J1655-40, GRS 1915+105 and XTE J1550-564. In our model a
non-axisymmetric magnetic coupling (MC) of a rotating black hole (BH) with its
surrounding accretion disc coexists with the Blandford-Znajek (BZ) process. The
upper frequency is fitted by a rotating hotspot near the inner edge of the
disc, which is produced by the energy transferred from the BH to the disc, and
the lower frequency is fitted by another rotating hotspot somewhere away from
the inner edge of the disc, which arises from the screw instability of the
magnetic field on the disc. It turns out that the 3:2 frequency ratio of HFQPOs
in these X-ray binaries could be well fitted to the observational data with a
much narrower range of the BH spin. In addition, the spectral properties of
HFQPOs are discussed. The correlation of HFQPOs with jets from microquasars is
contained naturally in our model.Comment: 8 pages, 4 figures. accepted by MNRA
Meson spectroscopy and properties using Dyson-Schwinger equations
We study pseudoscalar and scalar mesons using a practical and symmetry
preserving truncation of QCD's Dyson-Schwinger equations. We investigate and
compare properties of ground and radially excited meson states. In addition to
exact results for radial meson excitations we also present results for meson
masses and decay constants from the chiral limit up to the charm-quark mass, e.
g., the mass of the chi_{c0} (2P) meson.Comment: 8 pages, 3 figures, To appear in the proceedings of 9th International
Workshop on Meson Production, Properties and Interaction (Meson2006), Krakow,
Poland, 9 - 13 June 200
Phase diagram and excitations of a Shiba molecule
We analyze the phase diagram associated with a pair of magnetic impurities
trapped in a superconducting host. The natural interplay between Kondo
screening, superconductivity and exchange interactions leads to a rich array of
competing phases, whose transitions are characterized by discontinuous changes
of the total spin. Our analysis is based on a combination of numerical
renormalization group techniques as well as semi-classical analytics. In
addition to the expected screened and unscreened phases, we observe a new
molecular doublet phase where the impurity spins are only partially screened by
a single extended quasiparticle. Direct signatures of the various Shiba
molecule states can be observed via RF spectroscopy.Comment: 13 pages, 7 figure
Associated production of the charged Higgs boson and single top quark at the LHC
The left-right twin Higgs(LRTH) model predicts the existence of the charged
Higgs . In this paper, we study the production of the charged Higgs
boson with single top quark via the process at the
Large Hadron Collider(LHC). The numerical results show that the
production cross section can reach the level of in the reasonable
parameter space of the LRTH model. We expect that, as long as it is not too
heavy, the possible signatures of the heavy charged Higgs boson
might be detected via the decay mode at the LHC
experiments.Comment: This paper has been withdrawn by the author(s) due to some mistakes
in this pape
Direct Measurement of the Fermi Energy in Graphene Using a Double Layer Structure
We describe a technique which allows a direct measurement of the relative
Fermi energy in an electron system using a double layer structure, where
graphene is one of the two layers. We illustrate this method by probing the
Fermi energy as a function of density in a graphene monolayer, at zero and in
high magnetic fields. This technique allows us to determine the Fermi velocity,
Landau level spacing, and Landau level broadening in graphene. We find that the
N=0 Landau level broadening is larger by comparison to the broadening of upper
and lower Landau levels.Comment: 5 pages, 4 figure
Compositional closure for Bayes Risk in probabilistic noninterference
We give a sequential model for noninterference security including probability
(but not demonic choice), thus supporting reasoning about the likelihood that
high-security values might be revealed by observations of low-security
activity. Our novel methodological contribution is the definition of a
refinement order and its use to compare security measures between
specifications and (their supposed) implementations. This contrasts with the
more common practice of evaluating the security of individual programs in
isolation.
The appropriateness of our model and order is supported by our showing that
our refinement order is the greatest compositional relation --the compositional
closure-- with respect to our semantics and an "elementary" order based on
Bayes Risk --- a security measure already in widespread use. We also relate
refinement to other measures such as Shannon Entropy.
By applying the approach to a non-trivial example, the anonymous-majority
Three-Judges protocol, we demonstrate by example that correctness arguments can
be simplified by the sort of layered developments --through levels of
increasing detail-- that are allowed and encouraged by compositional semantics
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