511 research outputs found
Sarma Phase in Trapped Unbalanced Fermi Gases
We consider a trapped unbalanced Fermi gas at nonzero temperatures where the
superfluid Sarma phase is stable. We determine in particular the phase
boundaries between the superfluid, normal, and phase separated regions of the
trapped unbalanced Fermi mixture. We show that the physics of the Sarma phase
is sufficient to understand the recent observations of Zwierlein et al.
[Science 311, 492 (2006); Nature 442, 54 (2006)] and indicate how the apparent
contradictions between this experiment and the experiment of Partridge et al.
[Science 311, 503 (2006)] may be resolved.Comment: Replaced with published version; 4 pages, 3 figure
Investigating the intrinsic noise limit of Dayem bridge NanoSQUIDs
NanoSQUIDs made from Nb thin films have been produced with nanometre loop sizes down to 200 nm, using weak-link junctions with dimensions less than 60 nm. These composite (W/Nb) single layer thin film devices, patterned by FIB milling, show extremely good low-noise performance âŒ170 nΊ0 at temperatures between 5 and 8.5 K and can operate in rather high magnetic fields (at least up to 1 T). The devices produced so far have a limited operating temperature range, typically only 1â2 K. We have the goal of achieving operation at 4.2 K, to be compatible with the best SQUID series array (SSA) preamplifier available. Using the SSA to readout the nanoSQUIDs provides us with a means of investigating the intrinsic noise of the former. In this paper we report improved white noise levels of these nanoSQUIDs, enabling potential detection of a single electronic spin flip in a 1-Hz bandwidth. At low frequencies the noise performance is already limited by SSA preamplifier noise
Generalized gaugings and the field-antifield formalism
We discuss the algebra of general gauge theories that are described by the
embedding tensor formalism. We compare the gauge transformations dependent and
independent of an invariant action, and argue that the generic transformations
lead to an infinitely reducible algebra. We connect the embedding tensor
formalism to the field-antifield (or Batalin-Vilkovisky) formalism, which is
the most general formulation known for general gauge theories and their
quantization. The structure equations of the embedding tensor formalism are
included in the master equation of the field-antifield formalism.Comment: 42 pages; v2: some clarifications and 1 reference added; version to
be published in JHE
D-brane Wess--Zumino actions, T-duality and the cosmological constant
A geometrical formulation of the T-duality rules for type II superstring
Ramond--Ramond fields is presented. This is used to derive the Wess-Zumino
terms in superstring D-brane actions, including terms proportional to the mass
parameter of the IIA theory, thereby completing partial results in the
literature. For non-abelian world-volume gauge groups the massive type IIA
D-brane actions contain non-abelian Chern--Simons terms for the Born--Infeld
gauge potential, implying a quantization of the IIA cosmological constant.Comment: Version to be published in Physics Letters (minor corrections
Symmetric Potentials of Gauged Supergravities in Diverse Dimensions and Coulomb Branch of Gauge Theories
A class of conformally flat and asymptotically anti-de Sitter geometries
involving profiles of scalar fields is studied from the point of view of gauged
supergravity. The scalars involved in the solutions parameterise the
SL(N,R)/SO(N) submanifold of the full scalar coset of the gauged supergravity,
and are described by a symmetric potential with a universal form. These
geometries descend via consistent truncation from distributions of D3-branes,
M2-branes, or M5-branes in ten or eleven dimensions. We exhibit analogous
solutions asymptotic to AdS_6 which descend from the D4-D8-brane system. We
obtain the related six-dimensional theory by consistent reduction from massive
type IIA supergravity. All our geometries correspond to states in the Coulomb
branch of the dual conformal field theories. We analyze linear fluctuations of
minimally coupled scalars and find both discrete and continuous spectra, but
always bounded below.Comment: Latex, 38 pages, minor correction
Regularisation, the BV method, and the antibracket cohomology
We review the Lagrangian Batalin--Vilkovisky method for gauge theories. This
includes gauge fixing, quantisation and regularisation. We emphasize the role
of cohomology of the antibracket operation. Our main example is gravity,
for which we also discuss the solutions for the cohomology in the space of
local integrals. This leads to the most general form for the action, for
anomalies and for background charges.Comment: 12 pages, LaTeX, Preprint-KUL-TF-94/2
North Atlantic evidence for a for a unipolar icehouse climate state at the Eocene-Oligocene Transition
This is the final version. Available from Wiley via the DOI in this record.Earthâs climate transitioned from a warm unglaciated state to a colder glaciated âicehouseâ
state during the Cenozoic. Extensive ice sheets were first sustained on Antarctica at the
Eocene-Oligocene Transition (EOT, ~34 Ma), but there is intense debate over whether
Northern Hemisphere ice sheets developed simultaneously at this time, or tens of millions
of years later. Here we report on EOT-age sediments that contain detrital sand from
Integrated Ocean Drilling Program (IODP) Sites U1406 and U1411 on the Newfoundland
margin. These sites are ideally located to test competing hypotheses of the extent of Arctic
glaciation, being situated in the North Atlanticâs 'iceberg alley' where icebergs, calved from
both the Greenland Ice Sheet today, and the Laurentide Ice Sheet during the Pleistocene,
are concentrated by the Labrador Current and deposit continentally-derived detritus. Here
we show that detrital sand grains present in these EOT-aged sediments from the
Newfoundland margin, initially interpreted to represent ice rafting, were sourced from the
mid-latitudes of North America. We find that these grains were transported to the western
North Atlantic by fluvial and downslope processes, not icebergs, and were subsequently
reworked and deposited by deep-water contour currents on the Newfoundland margin.
Our findings are inconsistent with the presence of extensive ice sheets on southern and
western Greenland, and the northeastern Canadian Arctic. This contradicts extensive
bipolar glaciation at the EOT. The unipolar icehouse arose because of contrasting
latitudinal continental configurations at the poles, requiring more intense Cenozoic
climatic deterioration to trigger extensive Northern Hemisphere glaciation.Royal Societ
Photoionization of Rydberg atoms out of an optical dipole trap
Rydberg atoms are in the focus of intense research due to the peculiar
properties which make them interesting candidates for quantum optics and
quantum information applications. In this work we study the ionization of
Rydberg atoms due to their interaction with a trapping laser field, and a
reaction microscope is used to measure photoelectron angular and energy
distributions. Reaction microscopes are excellent tools when brandished against
atomic photoionization processes involving pulsed lasers; the timing tied to
each pulse is crucial in solving the subsequent equations of motion for the
atomic fragments in the spectrometer field. However, when used in pump-probe
schemes, which rely on continuous wave probe lasers, vital information linked
to the time of flight is lost. This study reports on a method in which the
standard ReMi technique is extended in time through coincidence measurements.
This is then applied to the photoionization of Li atoms initially prepared
in optically pumped and states. Multi-photon
excitation from a tunable femtosecond laser is exploited to produce Rydberg
atoms inside an infrared optical dipole trap; the structure and dynamics of the
subsequent cascade back towards ground is evaluated.Comment: 11 pages, 10 figure
Instantons and seven-branes in type IIB superstring theory
Instanton and seven-brane solutions of type IIB supergravity carrying charges
in the Ramond-Ramond sector are constructed. The singular seven-brane has a
quantized \RR \ \lq magnetic' charge whereas its dual is the instanton, which
is non-singular in the string frame and has an associated {\it global} \lq
electric' charge. The product of these charges is constrained by a Dirac
quantization condition. The instanton has the form of a space-time wormhole in
the string frame, and is responsible for the non-conservation of the Noether
current.Comment: PHYZZX macros. 13 pages. Final version as it will appear in Phys.
Lett. B (typos corrected
- âŠ