1,489 research outputs found
Measurements of ion mobility in argon and neon based gas mixtures
As gaseous detectors are operated at high rates of primary ionisation, ions
created in the detector have a considerable impact on the performance of the
detector. The upgraded ALICE Time Projection Chamber (TPC) will operate during
LHC Run with a substantial space charge density of positive ions in the
drift volume. In order to properly simulate such space charges, knowledge of
the ion mobility is necessary.
To this end, a small gaseous detector was constructed and the ion mobility of
various gas mixtures was measured. To validate the corresponding signal
analysis, simulations were performed.
Results are shown for several argon and neon based mixtures with different
fractions. A decrease of was measured for increasing water
content.Comment: 3 pages, 2 figure
Double quiver gauge theory and nearly Kahler flux compactifications
We consider G-equivariant dimensional reduction of Yang-Mills theory with
torsion on manifolds of the form MxG/H where M is a smooth manifold, and G/H is
a compact six-dimensional homogeneous space provided with a never integrable
almost complex structure and a family of SU(3)-structures which includes a
nearly Kahler structure. We establish an equivalence between G-equivariant
pseudo-holomorphic vector bundles on MxG/H and new quiver bundles on M
associated to the double of a quiver Q, determined by the SU(3)-structure, with
relations ensuring the absence of oriented cycles in Q. When M=R^2, we describe
an equivalence between G-invariant solutions of Spin(7)-instanton equations on
MxG/H and solutions of new quiver vortex equations on M. It is shown that
generic invariant Spin(7)-instanton configurations correspond to quivers Q that
contain non-trivial oriented cycles.Comment: 42 pages; v2: minor corrections; Final version to be published in
JHE
Quiver Gauge Theory of Nonabelian Vortices and Noncommutative Instantons in Higher Dimensions
We construct explicit BPS and non-BPS solutions of the Yang-Mills equations
on the noncommutative space R^{2n}_\theta x S^2 which have manifest spherical
symmetry. Using SU(2)-equivariant dimensional reduction techniques, we show
that the solutions imply an equivalence between instantons on R^{2n}_\theta x
S^2 and nonabelian vortices on R^{2n}_\theta, which can be interpreted as a
blowing-up of a chain of D0-branes on R^{2n}_\theta into a chain of spherical
D2-branes on R^{2n} x S^2. The low-energy dynamics of these configurations is
described by a quiver gauge theory which can be formulated in terms of new
geometrical objects generalizing superconnections. This formalism enables the
explicit assignment of D0-brane charges in equivariant K-theory to the
instanton solutions.Comment: 45 pages, 4 figures; v2: minor correction
Quiver Gauge Theory and Noncommutative Vortices
We construct explicit BPS and non-BPS solutions of the Yang-Mills equations
on noncommutative spaces R^{2n}_theta x G/H which are manifestly G-symmetric.
Given a G-representation, by twisting with a particular bundle over G/H, we
obtain a G-equivariant U(k) bundle with a G-equivariant connection over
R^{2n}_theta x G/H. The U(k) Donaldson-Uhlenbeck-Yau equations on these spaces
reduce to vortex-type equations in a particular quiver gauge theory on
R^{2n}_theta. Seiberg-Witten monopole equations are particular examples. The
noncommutative BPS configurations are formulated with partial isometries, which
are obtained from an equivariant Atiyah-Bott-Shapiro construction. They can be
interpreted as D0-branes inside a space-filling brane-antibrane system.Comment: talk by O.L. at the 21st Nishinomiya-Yukawa Memorial Symposium,
Kyoto, 15 Nov. 200
SU(3)-Equivariant Quiver Gauge Theories and Nonabelian Vortices
We consider SU(3)-equivariant dimensional reduction of Yang-Mills theory on
Kaehler manifolds of the form M x SU(3)/H, with H = SU(2) x U(1) or H = U(1) x
U(1). The induced rank two quiver gauge theories on M are worked out in detail
for representations of H which descend from a generic irreducible
SU(3)-representation. The reduction of the Donaldson-Uhlenbeck-Yau equations on
these spaces induces nonabelian quiver vortex equations on M, which we write
down explicitly. When M is a noncommutative deformation of the space C^d, we
construct explicit BPS and non-BPS solutions of finite energy for all cases. We
compute their topological charges in three different ways and propose a novel
interpretation of the configurations as states of D-branes. Our methods and
results generalize from SU(3) to any compact Lie group.Comment: 1+56 pages, 9 figures; v2: clarifying comments added, final version
to appear in JHE
Working with Nonassociative Geometry and Field Theory
We review aspects of our formalism for differential geometry on
noncommutative and nonassociative spaces which arise from cochain twist
deformation quantization of manifolds. We work in the simplest setting of
trivial vector bundles and flush out the details of our approach providing
explicit expressions for all bimodule operations, and for connections and
curvature. As applications, we describe the constructions of physically viable
action functionals for Yang-Mills theory and Einstein-Cartan gravity on
noncommutative and nonassociative spaces, as first steps towards more elaborate
models relevant to non-geometric flux deformations of geometry in closed string
theory.Comment: 20 pages; v2: Reference added; Contribution to the proceedings of the
Corfu Summer Institute on Elementary Particle Physics and Gravity, September
1-26, 2015, Corfu, Greece; Final version published in Proceedings of Scienc
Cheeger-Simons differential characters with compact support and Pontryagin duality
By adapting the Cheeger-Simons approach to differential cohomology, we
establish a notion of differential cohomology with compact support. We show
that it is functorial with respect to open embeddings and that it fits into a
natural diagram of exact sequences which compare it to compactly supported
singular cohomology and differential forms with compact support, in full
analogy to ordinary differential cohomology. We prove an excision theorem for
differential cohomology using a suitable relative version. Furthermore, we use
our model to give an independent proof of Pontryagin duality for differential
cohomology recovering a result of [Harvey, Lawson, Zweck - Amer. J. Math. 125
(2003) 791]: On any oriented manifold, ordinary differential cohomology is
isomorphic to the smooth Pontryagin dual of compactly supported differential
cohomology. For manifolds of finite-type, a similar result is obtained
interchanging ordinary with compactly supported differential cohomology.Comment: 33 pages, no figures - v3: Final version to be published in
Communications in Analysis and Geometr
Sasakian quiver gauge theories and instantons on cones over lens 5-spaces
We consider SU(3)-equivariant dimensional reduction of Yang-Mills theory over
certain cyclic orbifolds of the 5-sphere which are Sasaki-Einstein manifolds.
We obtain new quiver gauge theories extending those induced via reduction over
the leaf spaces of the characteristic foliation of the Sasaki-Einstein
structure, which are projective planes. We describe the Higgs branches of these
quiver gauge theories as moduli spaces of spherically symmetric instantons
which are SU(3)-equivariant solutions to the Hermitian Yang-Mills equations on
the associated Calabi-Yau cones, and further compare them to moduli spaces of
translationally-invariant instantons on the cones. We provide an explicit
unified construction of these moduli spaces as K\"ahler quotients and show that
they have the same cyclic orbifold singularities as the cones over the lens
5-spaces.Comment: v2: 54 pages, accepted for publication in Nuclear Physics
Radiation Generated by Charge Migration Following Ionization
Electronic many-body effects alone can be the driving force for an ultrafast
migration of a positive charge created upon ionization of molecular systems.
Here we show that this purely electronic phenomenon generates a characteristic
IR radiation. The situation when the initial ionic wave packet is produced by a
sudden removal of an electron is also studied. It is shown that in this case a
much stronger UV emission is generated. This emission appears as an ultrafast
response of the remaining electrons to the perturbation caused by the sudden
ionization and as such is a universal phenomenon to be expected in every
multielectron system.Comment: 5 pages, 4 figure
Sasakian quiver gauge theories and instantons on cones over round and squashed seven-spheres
We study quiver gauge theories on the round and squashed seven-spheres, and
orbifolds thereof. They arise by imposing -equivariance on the homogeneous
space endowed with its Sasaki-Einstein
structure, and as a 3-Sasakian manifold. In
both cases we describe the equivariance conditions and the resulting quivers.
We further study the moduli spaces of instantons on the metric cones over these
spaces by using the known description for Hermitian Yang-Mills instantons on
Calabi-Yau cones. It is shown that the moduli space of instantons on the
hyper-Kahler cone can be described as the intersection of three Hermitian
Yang-Mills moduli spaces. We also study moduli spaces of translationally
invariant instantons on the metric cone over
.Comment: 44 pages; v2: minor changes, reference added; Final version to appear
in Nuclear Physics
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