17,758 research outputs found
A New Gauge Mediation Theory
We propose a class of models with gauge mediation of supersymmetry breaking,
inspired by simple brane constructions, where R-symmetry is very weakly broken.
The gauge sector has an extended N=2 supersymmetry and the two electroweak
Higgses form an N=2 hypermultiplet, while quarks and leptons remain in N=1
chiral multiplets. Supersymmetry is broken via the D-term expectation value of
a secluded U(1) and it is transmitted to the Standard Model via gauge
interactions of messengers in N=2 hypermultiplets: gauginos thus receive Dirac
masses. The model has several distinct experimental signatures with respect to
ordinary models of gauge or gravity mediation realizations of the Minimal
Supersymmetric Standard Model (MSSM). First, it predicts extra states as a
third chargino that can be observed at collider experiments. Second, the
absence of a D-flat direction in the Higgs sector implies a lightest Higgs
behaving exactly as the Standard Model one and thus a reduction of the `little'
fine-tuning in the low tan(beta) region. This breaking of supersymmetry can be
easily implemented in string theory modelsComment: 23 pages, 3 figures, uses axodraw.sty. v2: a mistake in the radiative
generation of the scalar masses is corrected. The main conclusions are
unchange
Split extended supersymmetry from intersecting branes
We study string realizations of split extended supersymmetry, recently
proposed in hep-ph/0507192. Supersymmetry is broken by small ()
deformations of intersection angles of -branes giving tree-level masses of
order , where is the string scale, to localized
scalars. We show through an explicit one-loop string amplitude computation that
gauginos acquire hierarchically smaller Dirac masses . We also evaluate the one-loop Higgsino mass, , and show that,
in the absence of tree-level contributions, it behaves as . Finally we discuss an alternative suppression of scales using
large extra dimensions. The latter is illustrated, for the case where the gauge
bosons appear in N=4 representations, by an explicit string model with Standard
Model gauge group, three generations of quarks and leptons and gauge coupling
unification.Comment: 32 pages, 3 figure
Low-coverage heteroepitaxial growth with interfacial mixing
We investigate the influence of intermixing on heteroepitaxial growth
dynamics, using a two-dimensional point island model, expected to be a good
approximation in the early stages of epitaxy. In this model, which we explore
both analytically and numerically, every deposited B atom diffuses on the
surface with diffusion constant , and can exchange with any A atom
of the substrate at constant rate. There is no exchange back, and emerging
atoms diffuse on the surface with diffusion constant . When any two
diffusing atoms meet, they nucleate a point island. The islands neither diffuse
nor break, and grow by capturing other diffusing atoms. The model leads to an
island density governed by the diffusion of one of the species at low
temperature, and by the diffusion of the other at high temperature. We show
that these limit behaviors, as well as intermediate ones, all belong to the
same universality class, described by a scaling law. We also show that the
island-size distribution is self-similarly described by a dynamic scaling law
in the limits where only one diffusion constant is relevant to the dynamics,
and that this law is affected when both and play a
role.Comment: 16 pages, 6 figure
Wilson Fermions and Axion Electrodynamics in Optical Lattices
The formulation of massless relativistic fermions in lattice gauge theories
is hampered by the fundamental problem of species doubling, namely, the rise of
spurious fermions modifying the underlying physics. A suitable tailoring of the
fermion masses prevents such abundance of species, and leads to the so-called
Wilson fermions. Here we show that ultracold atoms provide us with the first
controllable realization of these paradigmatic fermions, thus generating a
quantum simulator of fermionic lattice gauge theories. We describe a novel
scheme that exploits laser-assisted tunneling in a cubic optical superlattice
to design the Wilson fermion masses. The high versatility of this proposal
allows us to explore a variety of interesting phases in three-dimensional
topological insulators, and to test the remarkable predictions of axion
electrodynamics.Comment: RevTex4 file, color figures, slightly longer than the published
versio
Theory of spin, electronic and transport properties of the lateral triple quantum dot molecule in a magnetic field
We present a theory of spin, electronic and transport properties of a
few-electron lateral triangular triple quantum dot molecule in a magnetic
field. Our theory is based on a generalization of a Hubbard model and the
Linear Combination of Harmonic Orbitals combined with Configuration Interaction
method (LCHO-CI) for arbitrary magnetic fields. The few-particle spectra
obtained as a function of the magnetic field exhibit Aharonov-Bohm
oscillations. As a result, by changing the magnetic field it is possible to
engineer the degeneracies of single-particle levels, and thus control the total
spin of the many-electron system. For the triple dot with two and four
electrons we find oscillations of total spin due to the singlet-triplet
transitions occurring periodically in the magnetic field. In the three-electron
system we find a transition from a magnetically frustrated to the
spin-polarized state. We discuss the impact of these phase transitions on the
addition spectrum and the spin blockade of the lateral triple quantum dot
molecule.Comment: 30 pages (one column), 9 figure
The S2N2 metallicity calibrator and the abundance gradient of M 33
We introduce the log(Ha/[SII]6717+6731) vs. log(Ha/[NII]6583) (S2N2)
diagnostic diagram as metallicity and ionisation parameter indicator for HII
regions in external galaxies. The location of HII regions in the S2N2 diagram
was studied both empirically and theoretically. We found that, for a wide range
of metallicities, the S2N2 diagram gives single valued results in the
metallicity-ionisation parameter plane. We demonstrate that the S2N2 diagram is
a powerful tool to estimate metallicities of high-redshift (z ~ 2) HII
galaxies. Finally, we derive the metallicity for 76 HII regions in M33 from the
S2N2 diagram and calculate an O/H abundance gradient for this galaxy of -0.05
(+-0.01) dex kpc^-1.Comment: 10 pages, 3 figures and 2 tables. Accepted for publication in MNRA
Long-time behavior of an angiogenesis model with flux at the tumor boundary
This paper deals with a nonlinear system of partial differential equations
modeling a simplified tumor-induced angiogenesis taking into account only the
interplay between tumor angiogenic factors and endothelial cells. Considered
model assumes a nonlinear flux at the tumor boundary and a nonlinear
chemotactic response. It is proved that the choice of some key parameters
influences the long-time behaviour of the system. More precisely, we show the
convergence of solutions to different semi-trivial stationary states for
different range of parameters.Comment: 17 page
The luminosity function of Palomar 5 and its tidal tails
We present the main sequence luminosity function of the tidally disrupted
globular cluster Palomar 5 and its tidal tails. For this work we analyzed
imaging data obtained with the Wide Field Camera at the INT (La Palma) and data
from the Wide Field Imager at the MPG/ESO 2.2 m telescope at La Silla down to a
limiting magnitude of approximately 24.5 mag in B. Our results indicate that
preferentially fainter stars were removed from the cluster so that the LF of
the cluster's main body exhibits a significant degree of flattening compared to
other GCs. This is attributed to its advanced dynamical evolution. The LF of
the tails is, in turn, enhanced with faint, low-mass stars, which we interpret
as a consequence of mass segregation in the cluster.Comment: 4 pages, 3 figures, to be published in the proceedings of the
conference "Satellites and tidal streams" held at La Palma, Canary Islands,
May 26 - 30, 200
CRLF2 rearrangement in Ph-like acute lymphoblastic leukemia predicts relative glucocorticoid resistance that is overcome with MEK or Akt inhibition.
Philadelphia chromosome-like (Ph-like) acute lymphoblastic leukemia (ALL) is a genetically heterogeneous subtype of B-cell ALL characterized by chromosomal rearrangements and mutations that result in aberrant cytokine receptor and kinase signaling. In particular, chromosomal rearrangements resulting in the overexpression of cytokine receptor-like factor 2 (CRLF2) occur in 50% of Ph-like ALL cases. CRLF2 overexpression is associated with particularly poor clinical outcomes, though the molecular basis for this is currently unknown. Glucocorticoids (GCs) are integral to the treatment of ALL and GC resistance at diagnosis is an important negative prognostic factor. Given the importance of GCs in ALL therapy and the poor outcomes for patients with CRLF2 overexpression, we hypothesized that the aberrant signal transduction associated with CRLF2 overexpression might mediate intrinsic GC insensitivity. To test this hypothesis, we exposed Ph-like ALL cells from patient-derived xenografts to GCs and found that CRLF2 rearranged (CRLF2R) leukemias uniformly demonstrated reduced GC sensitivity in vitro. Furthermore, targeted inhibition of signal transduction with the MEK inhibitor trametinib and the Akt inhibitor MK2206, but not the JAK inhibitor ruxolitinib, was sufficient to augment GC sensitivity. These data suggest that suboptimal GC responses may in part underlie the poor clinical outcomes for patients with CRLF2 overexpression and provide rationale for combination therapy involving GCs and signal transduction inhibitors as a means of enhancing GC efficacy
The Density Matrix Renormalization Group applied to single-particle Quantum Mechanics
A simplified version of White's Density Matrix Renormalization Group (DMRG)
algorithm has been used to find the ground state of the free particle on a
tight-binding lattice. We generalize this algorithm to treat the tight-binding
particle in an arbitrary potential and to find excited states. We thereby solve
a discretized version of the single-particle Schr\"odinger equation, which we
can then take to the continuum limit. This allows us to obtain very accurate
results for the lowest energy levels of the quantum harmonic oscillator,
anharmonic oscillator and double-well potential. We compare the DMRG results
thus obtained with those achieved by other methods.Comment: REVTEX file, 21 pages, 3 Tables, 4 eps Figure
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