7,854 research outputs found
On Finite 4D Quantum Field Theory in Non-Commutative Geometry
The truncated 4-dimensional sphere and the action of the
self-interacting scalar field on it are constructed. The path integral
quantization is performed while simultaneously keeping the SO(5) symmetry and
the finite number of degrees of freedom. The usual field theory UV-divergences
are manifestly absent.Comment: 18 pages, LaTeX, few misprints are corrected; one section is remove
Noncommutative Chiral Anomaly and the Dirac-Ginsparg-Wilson Operator
It is shown that the local axial anomaly in dimensions emerges naturally
if one postulates an underlying noncommutative fuzzy structure of spacetime .
In particular the Dirac-Ginsparg-Wilson relation on is shown to
contain an edge effect which corresponds precisely to the ``fuzzy''
axial anomaly on the fuzzy sphere . We also derive a novel gauge-covariant
expansion of the quark propagator in the form where
is the lattice spacing on , is
the covariant noncommutative chirality and is an effective
Dirac operator which has essentially the same IR spectrum as
but differes from it on the UV modes. Most remarkably is the fact that both
operators share the same limit and thus the above covariant expansion is not
available in the continuum theory . The first bit in this expansion
although it vanishes as it stands in the continuum
limit, its contribution to the anomaly is exactly the canonical theta term. The
contribution of the propagator is on the other hand
equal to the toplogical Chern-Simons action which in two dimensions vanishes
identically .Comment: 26 pages, latex fil
The One-loop UV Divergent Structure of U(1) Yang-Mills Theory on Noncommutative R^4
We show that U(1) Yang-Mills theory on noncommutative R^4 can be renormalized
at the one-loop level by multiplicative dimensional renormalization of the
coupling constant and fields of the theory. We compute the beta function of the
theory and conclude that the theory is asymptotically free. We also show that
the Weyl-Moyal matrix defining the deformed product over the space of functions
on R^4 is not renormalized at the one-loop level.Comment: 8 pages. A missing complex "i" is included in the field strength and
the divergent contributions corrected accordingly. As a result the model
turns out to be asymptotically fre
The Fuzzy Ginsparg-Wilson Algebra: A Solution of the Fermion Doubling Problem
The Ginsparg-Wilson algebra is the algebra underlying the Ginsparg-Wilson
solution of the fermion doubling problem in lattice gauge theory. The Dirac
operator of the fuzzy sphere is not afflicted with this problem. Previously we
have indicated that there is a Ginsparg-Wilson operator underlying it as well
in the absence of gauge fields and instantons. Here we develop this observation
systematically and establish a Dirac operator theory for the fuzzy sphere with
or without gauge fields, and always with the Ginsparg-Wilson algebra. There is
no fermion doubling in this theory. The association of the Ginsparg-Wilson
algebra with the fuzzy sphere is surprising as the latter is not designed with
this algebra in mind. The theory reproduces the integrated U(1)_A anomaly and
index theory correctly.Comment: references added, typos corrected, section 4.2 simplified. Report.no:
SU-4252-769, DFUP-02-1
A compact and robust diode laser system for atom interferometry on a sounding rocket
We present a diode laser system optimized for laser cooling and atom
interferometry with ultra-cold rubidium atoms aboard sounding rockets as an
important milestone towards space-borne quantum sensors. Design, assembly and
qualification of the system, combing micro-integrated distributed feedback
(DFB) diode laser modules and free space optical bench technology is presented
in the context of the MAIUS (Matter-wave Interferometry in Microgravity)
mission.
This laser system, with a volume of 21 liters and total mass of 27 kg, passed
all qualification tests for operation on sounding rockets and is currently used
in the integrated MAIUS flight system producing Bose-Einstein condensates and
performing atom interferometry based on Bragg diffraction. The MAIUS payload is
being prepared for launch in fall 2016.
We further report on a reference laser system, comprising a rubidium
stabilized DFB laser, which was operated successfully on the TEXUS 51 mission
in April 2015. The system demonstrated a high level of technological maturity
by remaining frequency stabilized throughout the mission including the rocket's
boost phase
System Tests of the ATLAS Pixel Detector
The innermost part of the ATLAS (A Toroidal LHC ApparatuS) experiment at the
LHC (Large Hadron Collider) will be a pixel detector, which is presently under
construction. Once installed into the experimental area, access will be
extremely limited. To ensure that the integrated detector assembly operates as
expected, a fraction of the detector which includes the power supplies and
monitoring system, the optical readout, and the pixel modules themselves, has
been assembled and operated in a laboratory setting for what we refer to as
system tests. Results from these tests are presented.Comment: 5 Pages, 9 Figures, to appear in Proceedings of the Eleventh Workshop
on Electronics for LHC and Future Experiment
BaFe_{1.8}Co_{0.2}As_2 thin film hybrid Josephson junctions
Josephson junctions with iron pnictides open the way for fundamental
experiments on superconductivity in these materials and their application in
superconducting devices. Here, we present hybrid Josephson junctions with a
BaFe_{1.8}Co_{0.2}As_2 thin film electrode, an Au barrier and a PbIn counter
electrode. The junctions show RSJ-like current-voltage characteristics up to
the critical temperature of the counter electrode of about 7.2K. The
temperature dependence of the critical current, IC, does not show an
Ambegaokar-Baratoff behavior. Well-pronounced Shapiro steps are observed at
microwave frequencies of 10-18GHz. Assuming an excess current, I_ex, of 200
{\mu}A at 4.2K we get an effective I_C R_N product of 6 {\mu}V.Comment: submitted to Appl. Phys. Let
Self similar Barkhausen noise in magnetic domain wall motion
A model for domain wall motion in ferromagnets is analyzed. Long-range
magnetic dipolar interactions are shown to give rise to self-similar dynamics
when the external magnetic field is increased adiabatically. The power spectrum
of the resultant Barkhausen noise is of the form , where
can be estimated from the critical exponents for interface
depinning in random media.Comment: 7 pages, RevTex. To appear in Phys. Rev. Let
L-functions of Symmetric Products of the Kloosterman Sheaf over Z
The classical -variable Kloosterman sums over the finite field
give rise to a lisse -sheaf on , which we call the Kloosterman
sheaf. Let be the
-function of the -fold symmetric product of . We
construct an explicit virtual scheme of finite type over such that the -Euler factor of the zeta function of coincides with
. We also prove
similar results for and .Comment: 16 page
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