1,171 research outputs found
Asymptotically free four-fermion interactions and electroweak symmetry breaking
We investigate the fermions of the standard model without a Higgs scalar.
Instead, we consider a non-local four-quark interaction in the tensor channel
which is characterized by a single dimensionless coupling . Quantization
leads to a consistent perturbative expansion for small . The running of
is asymptotically free and therefore induces a non-perturbative scale
, in analogy to the strong interactions. We argue that
spontaneous electroweak symmetry breaking is triggered at a scale where
grows large and find the top quark mass of the order of . We also
present a first estimate of the effective Yukawa coupling of a composite Higgs
scalar to the top quark, as well as the associated mass ratio between the top
quark and the W boson.Comment: 24 page
Measuring a photonic qubit without destroying it
Measuring the polarisation of a single photon typically results in its
destruction. We propose, demonstrate, and completely characterise a
\emph{quantum non-demolition} (QND) scheme for realising such a measurement
non-destructively. This scheme uses only linear optics and photo-detection of
ancillary modes to induce a strong non-linearity at the single photon level,
non-deterministically. We vary this QND measurement continuously into the weak
regime, and use it to perform a non-destructive test of complementarity in
quantum mechanics. Our scheme realises the most advanced general measurement of
a qubit: it is non-destructive, can be made in any basis, and with arbitrary
strength.Comment: 4 pages, 3 figure
Guiding neutral atoms around curves with lithographically patterned current-carrying wires
Laser-cooled neutral atoms from a low-velocity atomic source are guided via a
magnetic field generated between two parallel wires on a glass substrate. The
atoms bend around three curves, each with a 15-cm radius of curvature, while
traveling along a 10-cm-long track. A maximum flux of 2*10^6 atoms/sec is
achieved with a current density of 3*10^4 A/cm^2 in the
100x100-micrometer-cross-section wires. The kinetic energy of the guided atoms
in one transverse dimension is measured to be 42 microKelvin.Comment: 9 page
Simulated Annealing for Topological Solitons
The search for solutions of field theories allowing for topological solitons
requires that we find the field configuration with the lowest energy in a given
sector of topological charge. The standard approach is based on the numerical
solution of the static Euler-Lagrange differential equation following from the
field energy. As an alternative, we propose to use a simulated annealing
algorithm to minimize the energy functional directly. We have applied simulated
annealing to several nonlinear classical field theories: the sine-Gordon model
in one dimension, the baby Skyrme model in two dimensions and the nuclear
Skyrme model in three dimensions. We describe in detail the implementation of
the simulated annealing algorithm, present our results and get independent
confirmation of the studies which have used standard minimization techniques.Comment: 31 pages, LaTeX, better quality pics at
http://www.phy.umist.ac.uk/~weidig/Simulated_Annealing/, updated for
publicatio
Quantitative conditional quantum erasure in two-atom resonance fluorescence
We present a conditional quantum eraser which erases the a priori knowledge
or the predictability of the path a photon takes in a Young-type double-slit
experiment with two fluorescent four-level atoms. This erasure violates a
recently derived erasure relation which must be satisfied for a conventional,
unconditional quantum eraser that aims to find an optimal sorting of the system
into subensembles with particularly large fringe visibilities. The conditional
quantum eraser employs an interaction-free, partial which-way measurement which
not only sorts the system into optimal subsystems with large visibility but
also selects the appropriate subsystem with the maximum possible visibility. We
explain how the erasure relation can be violated under these circumstances.Comment: Revtex4, 12pages, 4 eps figures, replaced with published version,
changes in Sec. 3, to appear in Physical Review
MSLED, Neutrino Oscillations and the Cosmological Constant
We explore the implications for neutrino masses and mixings within the
minimal version of the supersymmetric large-extra-dimensions scenario (MSLED).
This model was proposed in {\tt hep-ph/0404135} to extract the phenomenological
implications of the promising recent attempt (in {\tt hep-th/0304256}) to
address the cosmological constant problem. Remarkably, we find that the
simplest couplings between brane and bulk fermions within this approach can
lead to a phenomenologically-viable pattern of neutrino masses and mixings that
is also consistent with the supernova bounds which are usually the bane of
extra-dimensional neutrino models. Under certain circumstances the MSLED
scenario can lead to a lepton mixing (PMNS) matrix close to the so-called
bi-maximal or the tri-bimaximal forms (which are known to provide a good
description of the neutrino oscillation data). We discuss the implications of
MSLED models for neutrino phenomenology.Comment: 38 pages, 1 figure; Reposted with a few additional reference
Quantitative wave-particle duality and non-erasing quantum erasure
The notion of wave-particle duality may be quantified by the inequality
V^2+K^2 <=1, relating interference fringe visibility V and path knowledge K.
With a single-photon interferometer in which polarization is used to label the
paths, we have investigated the relation for various situations, including
pure, mixed, and partially-mixed input states. A quantum eraser scheme has been
realized that recovers interference fringes even when no which-way information
is available to erase.Comment: 6 pages, 4 figures. To appear in Phys. Rev.
Observation of off-diagonal geometric phase in polarized neutron interferometer experiments
Off-diagonal geometric phases acquired in the evolution of a spin-1/2 system
have been investigated by means of a polarized neutron interferometer. Final
counts with and without polarization analysis enable us to observe
simultaneously the off-diagonal and diagonal geometric phases in two detectors.
We have quantitatively measured the off-diagonal geometric phase for noncyclic
evolutions, confirming the theoretical predictions. We discuss the significance
of our experiment in terms of geometric phases (both diagonal and off-diagonal)
and in terms of the quantum erasing phenomenon.Comment: pdf, 22 pages + 8 figures (included in the pdf). In print on Phys.
Rev.
Magnetothermodynamics of BPS baby skyrmions
The magnetothermodynamics of skyrmion type matter described by the gauged BPS
baby Skyrme model at zero temperature is investigated. We prove that the BPS
property of the model is preserved also for boundary conditions corresponding
to an asymptotically constant magnetic field. The BPS bound and the
corresponding BPS equations saturating the bound are found. Further, we show
that one may introduce pressure in the gauged model by a redefinition of the
superpotential. Interestingly, this is related to non-extremal type solutions
in the so-called fake supersymmetry method. Finally, we compute the equation of
state of magnetized BSP baby skyrmions inserted into an external constant
magnetic field and under external pressure , i.e., , where
is the "volume" (area) occupied by the skyrmions. We show that the BPS baby
skyrmions form a ferromagnetic medium.Comment: Latex, 39 pages, 14 figures. v2: New results and references added,
physical interpretation partly change
Importance of Follow-up Imaging in the Detection of Delayed Type 2 Endoleaks Despite Complete Aneurysmal Sac Shrinkage
Type 2 endoleaks usually constitute a benign and self-limited phenomenon, which rarely leads to aneurysmal sac expansion. However, in a small subset of patients, a persistent type 2 endoleak might pressurise the aneurysmal sac causing expansion. The authors present two cases with delayed new-onset type 2 endoleak. One occurred after standard endovascular aortic repair and the other after chimney endovascular aortic repair, causing expansion of the aneurysmal sac after a period of complete aneurysmal sac shrinkage. Accordingly, there is a risk of sac re-expansion due to delayed onset endoleaks, independent of the technique, justifying the need for a continuous follow-up despite long-term aneurysmal sac shrinkage
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