745 research outputs found
Non-conservation of Density of States in BiSrCaCuO: Coexistence of Pseudogap and Superconducting gap
The tunneling spectra obtained within the ab-plane of
BiSrCaCuO (Bi2212) for temperatures below and above the
critical temperature (T) are analyzed. We find that the tunneling
conductance spectra for the underdoped compound in the superconducting state do
not follow the conservation of states rule. There is a consistent loss of
states for the underdoped BI2212 implying an underlying depression in the
density of states (DOS) and hence the pseudogap near the Fermi energy (E).
Such an underlying depression can also explain the peak-dip-hump structure
observed in the spectra. Furthermore, the conservation of states is recovered
and the dip-hump structure disappears after normalizing the low temperature
spectra with that of the normal state. We argue that this is a direct evidence
for the coexistence of a pseudogap with the superconducting gap.Comment: 5 pages, 4 figure
Structure, stability and elasticity of DNA nanotube
DNA nanotubes are tubular structures composed of DNA crossover molecules. We
present a bottom up approach for construction and characterization of these
structures. Various possible topologies of nanotubes are constructed such as
6-helix, 8-helix and tri-tubes with different sequences and lengths. We have
used fully atomistic molecular dynamics simulations to study the structure,
stability and elasticity of these structures. Several nanosecond long MD
simulations give the microscopic details about DNA nanotubes. Based on the
structural analysis of simulation data, we show that 6-helix nanotubes are
stable and maintain their tubular structure; while 8-helix nanotubes are
flattened to stabilize themselves. We also comment on the sequence dependence
and effect of overhangs. These structures are approximately four times more
rigid having stretch modulus of ~4000 pN compared to the stretch modulus of
1000 pN of DNA double helix molecule of same length and sequence. The stretch
moduli of these nanotubes are also three times larger than those of PX/JX
crossover DNA molecules which have stretch modulus in the range of 1500-2000
pN. The calculated persistence length is in the range of few microns which is
close to the reported experimental results on certain class of the DNA
nanotubes.Comment: Published in Physical Chemistry Chemical Physic
Explaining the and anomalies with vector leptoquarks
Recently the factories BaBar and Belle as well as the LHCb experiment
have reported several anomalies in the semileptonic meson decays such as
and etc. We investigate these deviations by considering
the vector leptoquarks relevant for both and transitions. The leptoquark parameter space is constrained by using the
experimentally measured branching ratios of , and processes. Using the
constrained leptoquark couplings, we compute the branching ratios,
forward-backward asymmetries, and polarization parameters in the
processes. We find that the vector
leptoquarks can explain both and anomalies simultaneously.
Furthermore, we study the rare leptonic decay
processes in this model.Comment: 33 pages, 14 figures, typos correcte
Neutrino Mass Constraints on R violation and HERA anomaly
R parity violating trilinear couplings of the minimal
supersymmetric standard model (MSSM) are constrained from the limit on the
electron neutrino mass. Strong limits on these couplings follow from the
earlier neglected contribution due to sneutrino vacuum expectation values. The
limits on most of the couplings derived here are stronger than
the existing ones for a wide range in parameters of MSSM. These limits strongly
constrain the interpretation of recent HERA results in scattering in
terms of production of squarks through violating couplings. In particular,
the interpretation in terms of production off strange quark as
suggested recently is not viable for wide ranges in MSSM parameters.Comment: 15 pages with 5 figures, minor typos corrected and a new reference
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