3,207 research outputs found

### Statistical combination of searches for the $\rm{X^{\pm}(5568)}$ state decaying into $\rm{B^0_s \pi^\pm}$

A statistical combination of the search results for the narrow
$\rm{X^{\pm}(5568)}$ resonance decaying into $\rm{B_s^0 \pi^+}$ is reported,
based on published results from the ATLAS, CMS, CDF and LHCb Collaborations. A
structure in the invariant mass distribution of $\rm{B_s^0 \pi^+}$ has been
observed by the D0 Collaboration with a mass value of 5568 MeV but not
confirmed by any of the latest searches from the other Collaborations. Limits
have been set on the relative production rate $\rm{\rho_X}$ of the
$\rm{X^{\pm}(5568)}$ and $\rm{B^0_s}$ states, times the branching ratio for the
decay $\rm{X^{\pm}(5568) \rightarrow B^0_s\pi^\pm}$.
By applying a statistical combination of limits set by the three LHC
experiments, we derive a limit at 95\% Confidence Level of $\rho_X < 0.0092$
for $p_T(B^0_s)>$ 10 GeV, and $\rho_X$ 15 GeV,
superseding the previous most stringent upper limits. The effect of including
the CDF result in the combination is also discussed.Comment: 4 pages, 4 figures, 2 table

### Development of Micromegas detectors for the upgrade of the ATLAS Muon Spectrometer

The Muon Sepctrometer of the ATLAS detector will undergo a
major change in view of the LHC upgrade foreseen in 2018. In particular the two most internal detector wheels of the endcap part of the muon spectrometer (Small Wheels) need to be rebuilt with detectors capable to cope with the higher particle rate. We propose Micromegas detectors to be used both as trigger and tracking devices for the new Small Wheels. The most recent developments of Micromegas tailored to the ATLAS spectrometer upgrade will be illustrated: the development of resistive strip detectors to reduce the discharge probability, the construction of largesize
(∼ m2) chambers, the optimization of working parameters and the innovative μTPC working mode that allows a local reconstruction of track segments

### Microscopic Oscillations in the Quantum Nucleation of Vortices Subject to Periodic Pinning Potential in a Thin Superconductor

We present a theory for the decay of a supercurrent through nucleation of
vortex-antivortex pairs in a two-dimensional superconductor in the presence of
dissipation and of a periodic pinning potential. Through a powerful quantum
electrodynamics formulation of the problem we show that the nucleation rate
develops oscillations in its current-density dependence which are connected to
the pinning periodicity. A remnant of the dissipation-driven localization
transition is present, and an estimate of the nucleation rate suggests that
these effects might be observable in real thin superconductors.Comment: REVTeX file, 4 pages in two-column mode, 1 Postscript figure, to
appear in Phys.Rev.B (Rapid Communications

### Fermion Mass Hierarchy in Lifshitz Type Gauge Theory

We study the origin of fermion mass hierarchy and flavor mixing in a Lifshitz
type extension of the standard model including an extra scalar field. We show
that the hierarchical structure can originate from renormalizable interactions.
In contrast to the Froggatt-Nielsen mechanism, the higher the dimension of
associated operators, the heavier the fermion masses. Tiny masses for
left-handed neutrinos are obtained without introducing right-handed neutrinos.Comment: 13 pages; clarifications of some point

### Vortex Quantum Nucleation and Tunneling in Superconducting Thin Films: Role of Dissipation and Periodic Pinning

We investigate the phenomenon of decay of a supercurrent in a superconducting
thin film in the absence of an applied magnetic field. The resulting
zero-temperature resistance derives from two equally possible mechanisms: 1)
quantum tunneling of vortices from the edges of the sample; and 2) homogeneous
quantum nucleation of vortex-antivortex pairs in the bulk of the sample,
arising from the instability of the Magnus field's ``vacuum''. We study both
situations in the case where quantum dissipation dominates over the inertia of
the vortices. We find that the vortex tunneling and nucleation rates have a
very rapid dependence on the current density driven through the sample.
Accordingly, whilst normally the superconductor is essentially resistance-free,
for the high current densities that can be reached in high-$T_c$ films a
measurable resistance might develop. We show that edge-tunneling appears
favoured, but the presence of pinning centres and of thermal fluctuations leads
to an enhancement of the nucleation rates. In the case where a periodic pinning
potential is artificially introduced in the sample, we show that
current-oscillations will develop indicating an effect specific to the
nucleation mechanism where the vortex pair-production rate, thus the
resistance, becomes sensitive to the corrugation of the pinning substrate. In
all situations, we give estimates for the observability of the studied
phenomena.Comment: 8 pages (LaTeX), 2 postscript figures. Invited talk to the SATT8 (8th
Italian Meeting on High-T_c Superconductivity), Como (Italy), Villa Olmo, 1-4
October 1996, to be published in La Rivista del Nuovo Cimento

### Black hole - D-brane correspondence: An example

We explore the connection between D-branes and black holes in one particular
case: a $D3$-brane compactified to four dimensions on $T^6/Z_3$. Using the
$D$-brane boundary state description we show the equivalence with a double
extremal N=2 black hole solution of four dimensional supergravity.Comment: 15 pages, LaTeX. Contribution by C. Nunez to the conference Quantum
Gravity in the Southern Cone, Bariloche 7-10 January 1998; to appear in the
proceeding

### Electromagnetism and multiple-valued loop-dependent wave functionals

We quantize the Maxwell theory in the presence of a electric charge in a
"dual" Loop Representation, i.e. a geometric representation of magnetic
Faraday's lines. It is found that the theory can be seen as a theory without
sources, except by the fact that the wave functional becomes multivalued. This
can be seen as the dual counterpart of what occurs in Maxwell theory with a
magnetic pole, when it is quantized in the ordinary Loop Representation. The
multivaluedness can be seen as a result of the multiply-connectedness of the
configuration space of the quantum theory.Comment: 5 page

### Quantum Oscillator on \DC P^n in a constant magnetic field

We construct the quantum oscillator interacting with a constant magnetic
field on complex projective spaces \DC P^N, as well as on their non-compact
counterparts, i. e. the $N-$dimensional Lobachewski spaces ${\cal L}_N$. We
find the spectrum of this system and the complete basis of wavefunctions.
Surprisingly, the inclusion of a magnetic field does not yield any qualitative
change in the energy spectrum. For $N>1$ the magnetic field does not break the
superintegrability of the system, whereas for N=1 it preserves the exact
solvability of the system.
We extend this results to the cones constructed over \DC P^N and ${\cal
L}_N$, and perform the (Kustaanheimo-Stiefel) transformation of these systems
to the three-dimensional Coulomb-like systems.Comment: 9 pages, 1 figur

### Sommerfeld enhancement from Goldstone pseudo-scalar exchange

We point out that the exchange of a Goldstone pseudo-scalar can provide an
enhancement in the dark matter annihilation rate capable of explaining the
excess flux seen in high energy cosmic ray data. The mechanism of enhancement
involves the coupling of s and d waves through the tensor force that is very
strong and, in fact, singular at short distances. The results indicate that
large enhancements require some amount of fine tuning. We also discuss the
enhancement due to other singular attractive potentials, such as WIMP models
with a permanent electric dipole.Comment: 14 pages, 4 figures, v2 includes contact informatio

### The twisted open string partition function and Yukawa couplings

We use the operator formalism to derive the bosonic contribution to the
twisted open string partition function in toroidal compactifications. This
amplitude describes, for instance, the planar interaction between g+1
magnetized or intersecting D-branes. We write the result both in the closed and
in the open string channel in terms of Prym differentials on the appropriate
Riemann surface. Then we focus on the g=2 case for a 2-torus. By factorizing
the twisted partition function in the open string channel we obtain an explicit
expression for the 3-twist field correlator, which is the main ingredient in
the computation of Yukawa couplings in D-brane phenomenological models. This
provides an alternative method for computing these couplings that does not rely
on the stress-energy tensor technique.Comment: 32 pages, 5 figures, Latex; v2: typos correcte

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