2,127 research outputs found
Running surface couplings
We discuss the renormalization group improved effective action and running
surface couplings in curved spacetime with boundary. Using scalar
self-interacting theory as an example, we study the influence of the boundary
effects to effective equations of motion in spherical cap and the relevance of
surface running couplings to quantum cosmology and symmetry breaking
phenomenon. Running surface couplings in the asymptotically free SU(2) gauge
theory are found.Comment: 11 pages, Latex fil
Phases of supersymmetric O(N) theories
We perform a global renormalization group study of O(N) symmetric Wess-Zumino
theories and their phases in three euclidean dimensions. At infinite N the
theory is solved exactly. The phases and phase transitions are worked out for
finite and infinite short-distance cutoffs. A distinctive new feature arises at
strong coupling, where the effective superfield potential becomes multi-valued,
signalled by divergences in the fermion-boson interaction. Our findings resolve
the long-standing puzzle about the occurrence of degenerate O(N) symmetric
phases. At finite N, we find a strongly-coupled fixed point in the local
potential approximation and explain its impact on the phase transition. We also
examine the possibility for a supersymmetric Bardeen-Moshe-Bander phenomenon,
and relate our findings with the spontaneous breaking of supersymmetry in other
models.Comment: 23 pages, 18 figure
Relaxation measurements in the regime of the second magnetization peak in Nb films
We report on magnetic measurements as a function of field, temperature and
time (relaxation) in superconducting Nb films of critical temperature Tc = 9.25
K. The magnetic measurements as a function of field exhibited a second
magnetization peak (SMP) which in general is accompanied by thermomagnetic
instabilities (TMIs). The lines where the SMP occurs and where the first flux
jump in the virgin magnetization curves is observed, end at a characteristic
point (To,Ho)=(7.2 K,80 Oe). Relaxation measurements showed that for T<To=7.2 K
the activation energy Uo and the normalized relaxation rate S exhibit
non-monotonic behavior as a function either of temperature or field. The
extrema observed in Uo and S coincide with the onset and the maximum points of
the SMP. In the regime T>To=7.2 K both Uo and S present a conventional
monotonic behavior. These results indicate that the SMP behavior observed in
our Nb films is promoted by the anomalous relaxation of the magnetization.Comment: To appear in Physica
Tomographic readout of an opto-mechanical interferometer
The quantum state of light changes its nature when being reflected off a
mechanical oscillator due to the latter's susceptibility to radiation pressure.
As a result, a coherent state can transform into a squeezed state and can get
entangled with the motion of the oscillator. The complete tomographic
reconstruction of the state of light requires the ability to readout arbitrary
quadratures. Here we demonstrate such a readout by applying a balanced homodyne
detector to an interferometric position measurement of a thermally excited
high-Q silicon nitride membrane in a Michelson-Sagnac interferometer. A readout
noise of \unit{1.9 \cdot 10^{-16}}{\metre/\sqrt{\hertz}} around the
membrane's fundamental oscillation mode at \unit{133}{\kilo\hertz} has been
achieved, going below the peak value of the standard quantum limit by a factor
of 8.2 (9 dB). The readout noise was entirely dominated by shot noise in a
rather broad frequency range around the mechanical resonance.Comment: 7 pages, 5 figure
An all-optical trap for a gram-scale mirror
We report on a stable optical trap suitable for a macroscopic mirror, wherein
the dynamics of the mirror are fully dominated by radiation pressure. The
technique employs two frequency-offset laser fields to simultaneously create a
stiff optical restoring force and a viscous optical damping force. We show how
these forces may be used to optically trap a free mass without introducing
thermal noise; and we demonstrate the technique experimentally with a 1 gram
mirror. The observed optical spring has an inferred Young's modulus of 1.2 TPa,
20% stiffer than diamond. The trap is intrinsically cold and reaches an
effective temperature of 0.8 K, limited by technical noise in our apparatus.Comment: Major revision. Replacement is version that appears in Phy. Rev.
Lett. 98, 150802 (2007
Exploiting the convex-concave penalty for tracking: A novel dynamic reweighted sparse Bayesian learning algorithm
We propose a novel dynamic reweighted â„“2 (DRâ„“2) algorithm in the regime of dynamic compressive sensing. Our analysis shows that aiming to solve a Type II optimization problem, DRâ„“2 is effectively minimizing a `convex-concave' penalty in the coefficients that transitions from a convex region to a concave function using knowledge of past estimations. DRâ„“2 thus provides superior reconstruction performance compared with state-of-the-art dynamic CS algorithms.This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/ICASSP.2014.685422
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