786 research outputs found
Perturbative Approach For Non Renormalizable Theories
Renormalization procedure is generalized to be applicable for non
renormalizable theories. It is shown that introduction of an extra expansion
parameter allows to get rid of divergences and express physical quantities as
series of finite number of interdependent expansion parameters. Suggested
method is applied to quantum (Einstein's) gravity.Comment: 14 pages (LaTEX file
Implementation of a Gauss convoluted Pandel PDF for track reconstruction in Neutrino Telescopes
A probability distribution function is presented which provides a realistic
description of the detection of scattered photons. The resulting probabilities
can be described analytically by means of a superposition of several special
functions. These exact expressions can be evaluated numerically only for small
distances and limited time residuals, due to computer accuracy limitations. In
this report we provide approximations for the exact expressions in different
regions of the distance-time residual space, defined by the detector geometry
and the space-time scale of an event. These approximations can be evaluated
numerically with a relative error with respect to the exact expression at the
boundaries of less than 0.001.Comment: 9 pages, 4 figures Revision 1 : extended content 12 pages, 4 figures
Accepted for publication in Astroparticle Physic
Insulator-metal-insulator transition and selective spectral weight transfer in a disordered strongly correlated system
We investigate the metal insulator transitions at finite temperature for the
Hubbard model with diagonal alloy disorder. We solve the dynamical mean field
theory equations with the non crossing approximation and we use the coherent
potential approximation to handle disorder. The excitation spectrum is given
for various correlation strength and disorder. Two successive metal
insulator transitions are observed at integer filling values as is
increased. An important selective transfer of spectral weight arises upon
doping. The strong influence of the temperature on the low energy dynamics is
studied in details.Comment: submitted to Phys. Rev.
Band-Insulator-Metal-Mott-Insulator transition in the half--filled ionic-Hubbard chain
We investigate the ground state phase diagram of the half-filled
repulsive Hubbard model in the presence of a staggered ionic
potential , using the continuum-limit bosonization approach. We find,
that with increasing on-site-repulsion , depending on the value of the
next-nearest-hopping amplitude , the model shows three different
versions of the ground state phase diagram. For , the ground state phase diagram consists of the following
three insulating phases: Band-Insulator at , Ferroelectric Insulator
at . For
there is only one transition from a spin gapped
metallic phase at .
Finally, for intermediate values of the next-nearest-hopping amplitude
we find that with increasing
on-site repulsion, at the model undergoes a second-order
commensurate-incommensurate type transition from a band insulator into a
metallic state and at larger there is a Kosterlitz-Thouless type
transition from a metal into a ferroelectric insulator.Comment: 9 pages 3 figure
Long-range spin chirality dimer order in the Heisenberg chain with modulated Dzyaloshinskii-Moriya interactions
The ground-state phase diagram of a spin S = 1 2 XXZ Heisenberg chain with spatially modulated Dzyaloshinskii-Moriya interaction H= n{J(Sx nSx n+1 +Sy nSy n+1 )+JzSz nSz n+1 +[D0 +(−1)nD1](Sx nSy n+1 −S y nSx n+1 )}is studied using the continuum-limit bosonization approach and extensive density-matrix renormalizationgroupcomputations.Itisshownthattheeffectivecontinuum-limitbosonizedtheoryofthemodelisgivenby the double-frequency sine-Gordon model (DSG) where the frequencies, i.e., the scaling dimensions of the two competing cosine perturbation terms, depend on the effective anisotropy parameter γ∗ =Jz/ J2 +D2 0 +D2 1. Exploring the ground-state properties of the DSG model we show that the zero-temperature phase diagram contains the following four phases: (i) the ferromagnetic phase at γ∗ −1; (ii) the gapless Luttinger-liquid (LL) phase at−1 γ∗ C2 > 1 the gapped composite (C2) phase characterized in addition to the coexisting spin dimerization and alternating chirality patterns, by the presence of LRO antiferromagnetic order. The transition from the LL to the C1 phase at γ∗ C1 belongs to the Berezinskii-Kosterlitz-Thouless universality class, while the transition at γ∗ = γ∗ C2 from C1 to C2 phase is of the Ising type.Fil: Avalishvili, N.. Ilia State University; Georgia. Andronikashvili Institute of Physics; GeorgiaFil: Japaridze, G. I.. Ilia State University; Georgia. Andronikashvili Institute of Physics; GeorgiaFil: Rossini, Gerardo Luis. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto de FÃsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FÃsica La Plata; Argentin
POSSIBILITIES OF PURIFICATION OF HEAVY METALS CONTAMINATION IN SOILS
Methods of neutralisation of different types of soils contaminated with heavy metals are studied. Certain strains of microorganisms have been selected, local microflora has been studied and identified at the genus level in laboratory conditions. Considering the conducted works, development of modified forms of humic acids, stimulation of local microorganisms and creation of geochemical barriers using local natural raw materials is recomended. Obtained results makes possible to develop comprehensive and rational model by means of inovative technologies for effective purification of soils contaminated with heavy metals.Methods of neutralisation of different types of soils contaminated with heavy metals are studied. Certain strains of microorganisms have been selected, local microflora has been studied and identified at the genus level in laboratory conditions. Considering the conducted works, development of modified forms of humic acids, stimulation of local microorganisms and creation of geochemical barriers using local natural raw materials is recomended. Obtained results makes possible to develop comprehensive and rational model by means of inovative technologies for effective purification of soils contaminated with heavy metals
Space of State Vectors in PT Symmetrical Quantum Mechanics
Space of states of PT symmetrical quantum mechanics is examined. Requirement
that eigenstates with different eigenvalues must be orthogonal leads to the
conclusion that eigenfunctions belong to the space with an indefinite metric.
The self consistent expressions for the probability amplitude and average value
of operator are suggested. Further specification of space of state vectors
yield the superselection rule, redefining notion of the superposition
principle. The expression for the probability current density, satisfying
equation of continuity and vanishing for the bound state, is proposed.Comment: Revised version, explicit expressions for average values and
probability amplitude adde
Nature of the insulating phases in the half-filled ionic Hubbard model
We investigate the ground-state phase diagram of the one-dimensional "ionic"
Hubbard model with an alternating periodic potential at half-filling by
numerical diagonalization of finite systems with the Lanczos and density matrix
renormalization group (DMRG) methods. We identify an insulator-insulator phase
transition from a band to a correlated insulator with simultaneous charge and
bond-charge order. The transition point is characterized by the vanishing of
the optical excitation gap while simultaneously the charge and spin gaps remain
finite and equal. Indications for a possible second transition into a
Mott-insulator phase are discussed.Comment: final for
Wilson Loops in N=2 Super-Yang-Mills from Matrix Model
We compute the expectation value of the circular Wilson loop in N=2
supersymmetric Yang-Mills theory with N_f=2N hypermultiplets. Our results
indicate that the string tension in the dual string theory scales as the
logarithm of the 't Hooft coupling.Comment: 37 pages, 9 figures; v2: Numerical factors corrected, simple
derivation of Wilson loop and discussion of continuation to complex lambda
added; v3: instanton partition function re-analyzed in order to take into
account a contribution of the hypermultiplet
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