36,378 research outputs found
Thermodynamic properties of Holstein polarons and the effects of disorder
The ground state and finite temperature properties of polarons are studied
considering a two-site and a four-site Holstein model by exact diagonalization
of the Hamiltonian. The kinetic energy, Drude weight, correlation functions
involving charge and lattice deformations, and the specific heat have been
evaluated as a function of electron-phonon (e-ph) coupling strength and
temperature. The effects of site diagonal disorder on the above properties have
been investigated. The disorder is found to suppress the kinetic energy and the
Drude weight, reduces the spatial extension of the polaron, and makes the
large-to-small polaron crossover smoother. Increasing temperature also plays
similar role. For strong coupling the kinetic energy arises mainly from the
incoherent hopping processes owing to the motion of electrons within the
polaron and is almost independent of the disorder strength. From the coherent
and incoherent contributions to the kinetic energy, the temperature above which
the incoherent part dominates is determined as a function of e-ph coupling
strength.Comment: 17 pages. 17 figure
Radio Observations of AGN in Low Surface Brightness Galaxies
We present preliminary results of a study of the low frequency radio
continuum emission from the nuclei of Giant Low Surface Brightness (LSB)
galaxies. We have mapped the emission and searched for extended features such
as radio lobes/jets associated with AGN activity. LSB galaxies are poor in star
formation and generally less evolved compared to nearby bright spirals. This
paper presents low frequency observations of 3 galaxies; PGC 045080 at 1.4 GHz,
610 MHz, 325MHz, UGC 1922 at 610 MHz and UGC 6614 at 610 MHz. The observations
were done with the GMRT. Radio cores as well as extended structures were
detected and mapped in all three galaxies; the extended emission may be
assocated with jets/lobes associated with AGN activity. Our results indicate
that although these galaxies are optically dim, their nuclei can host AGN that
are bright in the radio domain.Comment: To appear in proceedings IAU Symp 244, 'Dark Galaxies and Lost
Baryons', June 2007, 2 pages including 1 figur
Scalar sector properties of two-Higgs-doublet models with a global U(1) symmetry
We analyze the scalar sector properties of a general class of
two-Higgs-doublet models which has a global U(1) symmetry in the quartic terms.
We find constraints on the parameters of the potential from the considerations
of unitarity of scattering amplitudes, the global stability of the potential
and the -parameter. We concentrate on the spectrum of the non-standard
scalar masses in the decoupling limit which is preferred by the Higgs data at
the LHC. We exhibit charged-Higgs induced contributions to the diphoton decay
width of the 125\,GeV Higgs boson and its correlation with the corresponding
width.Comment: 12 pages, 15 eps figure files; minor modifications made and a few
references adde
Radio Observations of the AGN and Gas in Low Surface Brightness Galaxies
LSB galaxies have low metallicities, diffuse stellar disks, and massive HI
disks. We have detected molecular gas in two giant LSB galaxies, UGC 6614 and
F568-6. A millimeter continuum source has been detected in UGC 6614 as well. At
centimeter wavelengths we have detected and mapped the continuum emission from
the giant LSB galaxy 1300+0144. The emission is extended about the nucleus and
is most likely originating from the AGN in the galaxy. The HI gas distribution
and velocity field in 1300+0144 was also mapped. The HI disk extends well
beyond the optical disk and appears lopsided in the intensity maps.Comment: one page; submitted to proceedings of IAU Symposium 235: Galaxy
Evolution across the Hubble Tim
Controlled Flow of Spin-Entangled Electrons via Adiabatic Quantum Pumping
We propose a method to dynamically generate and control the flow of
spin-entangled electrons, each belonging to a spin-singlet, by means of
adiabatic quantum pumping. The pumping cycle functions by periodic time
variation of localized two-body interactions. We develop a generalized approach
to adiabatic quantum pumping as traditional methods based on scattering matrix
in one dimension cannot be applied here. We specifically compute the flow of
spin-entangled electrons within a Hubbard-like model of quantum dots, and
discuss possible implementations and identify parameters that can be used to
control the singlet flow.Comment: 4 pages, 3 figure
Hamiltonian Analysis of Non-Linear Sigma Model on Supercoset Target
This paper is devoted to the study of the Hamiltonian formulation of
non-linear sigma models on supercoset targets. We calculate the Poisson
brackets of left-invariant currents. Then we introduce the Hamiltonian of the
system and determine the equations of motion for left-invariant currents. We
also determine the charge corresponding to the invariance of the action under
global left multiplication.Comment: 17. pages,v2: references added, v3: references added, minor
correction
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