12,569 research outputs found
An Effective Cutoff for the Isolalated Lepton Background from Bottom Decay --
There is a strong correlation between the and isolation of the lepton
coming from decay. Consequently the isolated lepton background from
decay goes down rapidly with increasing lepton ; and there is a
cutoff beyond which it effectively vanishes. For the isolation cut of GeV, appropriate for LHC, the lepton cutoff is 80 GeV. This can be
exploited to effectively eliminate the background from the like sign
dilepton channel apropriate for Majorana particle searches, as well as the
unlike sign dilepton and the single lepton channels appropriate for the top
quark search. We illustrate this with a detailed analysis of the background
in these channels along with the signals at LHC energy using both parton level
MC and ISAJET programs.Comment: TIFR/TH/93-23 (LATEX, 20 pages, 7 figures available on request
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
on the surface of a topological insulator across a ferromagnetic strip
providing an exchange field over a region of width . We show
that the conductance of such a junction changes from oscillatory to a
monotonically decreasing function of beyond a critical . 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 and potential in the presence of such a
ferromagnetic strip and show that beyond a critical , the
criteria of conductance maxima changes from
to for integer . 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
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 , the transport can be controlled using the exchange field
of a ferromagnetic film over a region of width . The
conductance of such a junction changes from oscillatory to a monotonically
decreasing function of beyond a critical which leads to the
possible realization of magnetic switches using these junctions. For NBM
junctions with a potential barrier of width and potential , we find
that beyond a critical , the criteria of conductance maxima
changes from to for
integer . 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
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 , with with a
possible cross-over to at late times. We argue that the
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
Relating transverse structure of various parton distributions
We present the results of T-even TMDs in a light front quark-diquark model of
nucleons with the wave functions constructed from the soft-wall AdS/QCD
prediction. The relations amongst TMDs are discussed. The dependence
of the TMDs are compared with the -dependence of the GPDs. AdS/QCD wave
function provides an explanation behind the approximate and
factorization observed in lattice TMD calculations.Comment: 11 pages, 8 figures, modified extensively, added new results and
discusssion
On Upward Drawings of Trees on a Given Grid
Computing a minimum-area planar straight-line drawing of a graph is known to
be NP-hard for planar graphs, even when restricted to outerplanar graphs.
However, the complexity question is open for trees. Only a few hardness results
are known for straight-line drawings of trees under various restrictions such
as edge length or slope constraints. On the other hand, there exist
polynomial-time algorithms for computing minimum-width (resp., minimum-height)
upward drawings of trees, where the height (resp., width) is unbounded.
In this paper we take a major step in understanding the complexity of the
area minimization problem for strictly-upward drawings of trees, which is one
of the most common styles for drawing rooted trees. We prove that given a
rooted tree and a grid, it is NP-hard to decide whether
admits a strictly-upward (unordered) drawing in the given grid.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
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