9,514 research outputs found

### Revisiting LHC gluino mass bounds through radiative decays using MadAnalysis 5

The ATLAS and CMS experiments at the CERN LHC have collected about 25 inverse
femtobarns (fb) of data each at the end of their 8 TeV run, and ruled out a
huge swath of parameter space in the context of Minimally Supersymmetric
Standard Model (MSSM). Limits on masses of the gluino have been pushed to above
1 TeV. These limits are however extremely model dependent and do not always
reflect the level of exclusion. So far the limits on the gluino mass using the
simplified model approach only constrained its value using its three-body
decays. We show in this work that already existing ATLAS and CMS analysis can
also constrain the radiative gluino decay mode and we derived improved mass
limits in particular when the mass difference between the LSP and the gluino is
small.Comment: 4 pages, 3 figures. To appear in the proceedings of the 27th
Rencontres the Blois on Particle Physics and Cosmology, May 31 - June 05,
201

### Field Induced Supersolid Phase in Spin-One Heisenberg Models

We use quantum Monte Carlo methods to demonstrate that the quantum phase
diagram of the S=1 Heisenberg model with uniaxial anisotropy contains an
extended supersolid phase. We also show that this Hamiltonian is a particular
case of a more general and ubiquitous model that describes the low energy
spectrum of a class of {\it isotropic} and {\it frustrated} spin systems. This
crucial result provides the required guidance for finding experimental
realizations of a spin supersolid state.Comment: 4 pages, 4 figure

### Spinning Test Particle in Kalb-Ramond background

In this work we explore the geodesic deviations of spinning test particles in
a string inspired Einstein-Kalb Ramond background. Such a background is known
to be equivalent to a spacetime geometry with torsion. We have shown here that
the antisymmetric Kalb-Ramond field has significant effect on the geodesic
deviation of a spinning test particle. A search for an observational evidence
of such an effect in astrophysical experiments may lead to a better
undestanding of the geometry of the background spacetime.Comment: 14 pages, Latex, 5 figure

### Magnetotransport of Dirac Fermions on the surface of a topological insulator

We study the properties of Dirac fermions on the surface of a topological
insulator in the presence of crossed electric and magnetic fields. We provide
an exact solution to this problem and demonstrate that, in contrast to their
counterparts in graphene, these Dirac fermions allow relative tuning of the
orbital and Zeeman effects of an applied magnetic field by a crossed electric
field along the surface. We also elaborate and extend our earlier results on
normal metal-magnetic film-normal metal (NMN) and normal metal-barrier-magnetic
film (NBM) junctions of topological insulators [Phys. Rev. Lett. {\bf 104},
046403 (2010)]. For NMN junctions, we show that for Dirac fermions with Fermi
velocity $v_F$, the transport can be controlled using the exchange field
${\mathcal J}$ of a ferromagnetic film over a region of width $d$. The
conductance of such a junction changes from oscillatory to a monotonically
decreasing function of $d$ beyond a critical ${\mathcal J}$ which leads to the
possible realization of magnetic switches using these junctions. For NBM
junctions with a potential barrier of width $d$ and potential $V_0$, we find
that beyond a critical ${\mathcal J}$, the criteria of conductance maxima
changes from $\chi= e V_0 d/\hbar v_F = n \pi$ to $\chi= (n+1/2)\pi$ for
integer $n$. Finally, we compute the subgap tunneling conductance of a normal
metal-magnetic film-superconductor (NMS) junctions on the surface of a
topological insulator and show that the position of the peaks of the zero-bias
tunneling conductance can be tuned using the magnetization of the ferromagnetic
film. We point out that these phenomena have no analogs in either conventional
two-dimensional materials or Dirac electrons in graphene and suggest
experiments to test our theory.Comment: 11 pages, 12 figures; v

### Tuning the conductance of Dirac fermions on the surface of a topological insulator

We study the transport properties of the Dirac fermions with Fermi velocity
$v_F$ on the surface of a topological insulator across a ferromagnetic strip
providing an exchange field ${\mathcal J}$ over a region of width $d$. We show
that the conductance of such a junction changes from oscillatory to a
monotonically decreasing function of $d$ beyond a critical ${\mathcal J}$. This
leads to the possible realization of a magnetic switch using these junctions.
We also study the conductance of these Dirac fermions across a potential
barrier of width $d$ and potential $V_0$ in the presence of such a
ferromagnetic strip and show that beyond a critical ${\mathcal J}$, the
criteria of conductance maxima changes from $\chi= e V_0 d/\hbar v_F = n \pi$
to $\chi= (n+1/2)\pi$ for integer $n$. We point out that these novel phenomena
have no analogs in graphene and suggest experiments which can probe them.Comment: v1 4 pages 5 fig

### Single-file diffusion and kinetics of template assisted assembly of colloids

We report computer simulation studies of the kinetics of ordering of a two
dimensional system of particles on a template with a one dimensional periodic
pattern. In equilibrium one obtains a re-entrant liquid-solid-liquid phase
transition as the strength of the substrate potential is varied. We show that
domains of crystalline order grow as $\sim t^{1/z}$, with $z \sim 4$ with a
possible cross-over to $z \sim 2$ at late times. We argue that the $t^{1/4}$
law originates from {\em single-file} motion and annihilation of defect pairs
of opposite topological charge along channels created by the template.Comment: 4 pages pdflatex 4 pdf figure

### Modulus stabilization of generalized Randall Sundrum model with bulk scalar field

We study the stabilization of inter-brane spacing modulus of generalized
warped brane models with a nonzero brane cosmological constant. Employing
Goldberger-Wise stabilization prescription of brane world models with a bulk
scalar field, we show that the stabilized value of the modulus generally
depends on the value of the brane cosmological constant. Our result further
reveals that the stabilized modulus value corresponding to a vanishingly small
cosmological constant can only resolve the gauge hierarchy problem
simultaneously. This in turn vindicates the original Randall-Sundrum model
where the 3-brane cosmological constant was chosen to be zero.Comment: 12 Pages, 1 figure, Revtex, Version to appear in Euro. Phys. Let

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