1,159 research outputs found
Specific heat across the superconducting dome in the cuprates
The specific heat of the superconducting cuprates is calculated over the
entire phase diagram. A d-wave BCS approach based on the large Fermi surface of
Fermi liquid and band structure theory provides a good description of the
overdoped region. At underdoping it is essential to include the emergence of a
second energy scale, the pseudogap and its associated Gutzwiller factor, which
accounts for a reduction in the coherent piece of the electronic Green's
function due to increased correlations as the Mott insulating state is
approached. In agreement with experiment, we find that the slope of the linear
in T dependence of the low temperature specific heat rapidly increases above
optimum doping while it is nearly constant below optimum. Our theoretical
calculations also agree with recent data on BiSrLaCuO for which the normal state is accessed through the
application of a large magnetic field. A quantum critical point is located at a
doping slightly below optimum.Comment: submitted to PRB; 8 pages, 5 figure
Evidence for Multiple Mergers among Ultraluminous IR Galaxies (ULIRGs): Remnants of Compact Groups?
In a large sample of ULIRGs imaged with HST, we have identified a significant
subsample that shows evidence for multiple mergers. The evidence is seen among
two classes of ULIRGs: (1) those with multiple remnant nuclei in their core,
sometimes accompanied by a complex system of tidal tails; and (2) those that
are in fact dense groupings of interacting (soon-to-merge) galaxies. We
conservatively estimate that, in the redshift range 0.05<z<0.20, at least 20
(out of 99) ULIRGs satisfy one or both of these criteria. We present several
cases and discuss the possibility that the progenitors of ULIRGs may be the
more classical weakly interacting compact groups of galaxies (Hickson 1997). An
evolutionary progression is consistent with the results: from compact groups to
pairs to ULIRGs to ellipticals. The last step follows the blowout of gas and
dust from the ULIRG.Comment: 5 pages, including 1 color postscript figure. Published in the
Astrophysical Journal Letters (1 Feb 2000). Replaced with final edited
version, including corrected typos and additional references, plus the color
figure has been improved and is only available her
Efficient ion-photon qubit SWAP gate in realistic ion cavity-QED systems without strong coupling
We present a scheme for deterministic ion-photon qubit exchange, namely a
SWAP gate, based on realistic cavity-QED systems with 171Yb+, 40Ca+ and 138Ba+
ions. The gate can also serve as a single-photon quantum memory, in which an
outgoing photon heralds the successful arrival of the incoming photonic qubit.
Although strong coupling, namely having the single-photon Rabi frequency be the
fastest rate in the system, is often assumed essential, this gate (similarly to
the Duan-Kimble C-phase gate) requires only Purcell enhancement, i.e. high
single-atom cooperativity. Accordingly, it does not require small mode volume
cavities, which are challenging to incorporate with ions due to the difficulty
of trapping them close to dielectric surfaces. Instead, larger cavities,
potentially more compatible with the trap apparatus, are sufficient, as long as
their numerical aperture is high enough to maintain small mode area at the
ion's position. We define the optimal parameters for the gate's operation and
simulate the expected fidelities and efficiencies, demonstrating that efficient
photon-ion qubit exchange, a valuable building block for scalable quantum
computation, is practically attainable with current experimental capabilities.Comment: 18 pages, 9 figure
A Hubble Space Telescope Snapshot Survey of Dynamically Close Galaxy Pairs in the CNOC2 Redshift Survey
We compare the structural properties of two classes of galaxies at
intermediate redshift: those in dynamically close galaxy pairs, and those which
are isolated. Both samples are selected from the CNOC2 Redshift Survey, and
have redshifts in the range 0.1 < z <0.6. Hubble Space Telescope WFPC2 images
were acquired as part of a snapshot survey, and were used to measure bulge
fraction and asymmetry for these galaxies. We find that paired and isolated
galaxies have identical distributions of bulge fractions. Conversely, we find
that paired galaxies are much more likely to be asymmetric (R_T+R_A >= 0.13)
than isolated galaxies. Assuming that half of these pairs are unlikely to be
close enough to merge, we estimate that 40% +/- 11% of merging galaxies are
asymmetric, compared with 9% +/- 3% of isolated galaxies. The difference is
even more striking for strongly asymmetric (R_T+R_A >= 0.16) galaxies: 25% +/-
8% for merging galaxies versus 1% +/- 1% for isolated galaxies. We find that
strongly asymmetric paired galaxies are very blue, with rest-frame B-R colors
close to 0.80, compared with a mean (B-R)_0 of 1.24 for all paired galaxies. In
addition, asymmetric galaxies in pairs have strong [OII]3727 emission lines. We
conclude that close to half of the galaxy pairs in our sample are in the
process of merging, and that most of these mergers are accompanied by triggered
star formation.Comment: Accepted for publication in the Astronomical Journal. 40 pages,
including 15 figures. For full resolution version, please see
http://www.trentu.ca/physics/dpatton/hstpairs
Dark Matter and Dark Energy via Non-Perturbative (Flavour) Vacua
A non-perturbative field theoretical approach to flavour physics
(Blasone-Vitiello formalism) has been shown to imply a highly non-trivial
vacuum state. In a previous work, we implemented the approach on a simple
supersymmetric model (free Wess-Zumino), with flavour mixing, which was
regarded as a model for free neutrinos and sneutrinos. The resulting effective
vacuum (called "flavour vacuum") was found to be characterized by a strong SUSY
breaking. In this paper we explore the phenomenology of the model and we argue
that the flavour vacuum is a consistent source for both Dark Energy (thanks to
the bosonic sector of the model) and Dark Matter (via the fermionic one). Quite
remarkably, besides the parameters connected with neutrino physics, in this
model no other parameters have been introduced, possibly leading to a
predictive theory of Dark Energy/Matter. Despite its oversimplification, such a
toy model already seems capable to shed some light on the observed energy
hierarchy between neutrino physics, Dark Energy and Dark Matter. Furthermore,
we move a step forth in the construction of a more realistic theory, by
presenting a novel approach for calculating relevant quantities and hence
extending some results to interactive theories, in a completely
non-perturbative way.Comment: 14 pages, 2 figure
Leptin and Hypertension in Obesity
Leptin, a peptide discovered more than 10 years ago, decreases food intake and increases sympathetic nerve activity to both thermogenic and nonthermogenic tissue. Leptin was initially believed to be an anti-obesity hormone, owing to its metabolic effects. However, obese individuals, for unknown reasons, become resistant to the satiety and weight-reducing effect of the hormone, but preserve leptin-mediated sympathetic activation to nonthermogenic tissue such as kidney, heart, and adrenal glands. Leptin has been shown to influence nitric oxide production and natriuresis, and along with chronic sympathetic activation, especially to the kidney, it may lead to sodium retention, systemic vasoconstriction, and blood pressure elevation. Consequently, leptin is currently considered to play an important role in the development of hypertension in obesity
HST Observations of the Serendipitous X-ray Companion to Mrk 273: Cluster at z=0.46?
We have used HST I-band images to identify Mrk 273X, the very unusual
high-redshift X-ray-luminous Seyfert 2 galaxy found by ROSAT in the same
field-of-view as Mrk 273. We have measured the photometric properties of Mrk
273X and have also analyzed the luminosity distribution of the faint galaxy
population seen in the HST image. The luminosity of the galaxy and the
properties of the surrounding environment suggest that Mrk 273X is the
brightest galaxy in a relatively poor cluster at a redshift near 0.46. Its
off-center location in the cluster and the presence of other galaxy groupings
in the HST image may indicate that this is a dynamically young cluster on the
verge of merging with its neighboring clusters. We find that Mrk 273X is a
bright featureless elliptical galaxy with no evidence for a disk. It follows
the de Vaucouleurs (r^{1/4}) surface brightness law very well over a range of 8
magnitudes. Though the surface brightness profile does not appear to be
dominated by the AGN, the galaxy has very blue colors that do appear to be
produced by the AGN. Mrk 273X is most similar to the IC 5063 class of active
galaxies --- a hybrid Sy 2 / powerful radio galaxy.Comment: Accepted for publication in the Astrophysical Journal. 8 pages,
including 4 postscript figures. Uses emulateapj.sty and psfig.sty. Higher
quality version of Figure 1 is available at
http://rings.gsfc.nasa.gov/~borne/fig1-markgals.gi
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