1,405 research outputs found
Implicit self-consistent electrolyte model in plane-wave density-functional theory
The ab-initio computational treatment of electrochemical systems requires an
appropriate treatment of the solid/liquid interfaces. A fully quantum
mechanical treatment of the interface is computationally demanding due to the
large number of degrees of freedom involved. In this work, we describe a
computationally efficient model where the electrode part of the interface is
described at the density-functional theory (DFT) level, and the electrolyte
part is represented through an implicit solvation model based on the
Poisson-Boltzmann equation. We describe the implementation of the linearized
Poisson-Boltzmann equation into the Vienna Ab-initio Simulation Package (VASP),
a widely used DFT code, followed by validation and benchmarking of the method.
To demonstrate the utility of the implicit electrolyte model, we apply it to
study the surface energy of Cu crystal facets in an aqueous electrolyte as a
function of applied electric potential. We show that the applied potential
enables the control of the shape of nanocrystals from an octahedral to a
truncated octahedral morphology with increasing potential
Relating on-shell and off-shell formalism in perturbative quantum field theory
In the on-shell formalism (mostly used in perturbative quantum field theory)
the entries of the time ordered product T are on-shell fields (i.e. the basic
fields satisfy the free field equations). With that, (multi)linearity of T is
incompatible with the Action Ward identity. This can be circumvented by using
the off-shell formalism in which the entries of T are off-shell fields. To
relate on- and off-shell formalism correctly, a map sigma from on-shell fields
to off-shell fields was introduced axiomatically by Duetsch and Fredenhagen. In
that paper it was shown that, in the case of one real scalar field in N=4
dimensional Minkowski space, these axioms have a unique solution. However, this
solution was given there only recursively. We solve this recurrence relation
and give a fully explicit expression for sigma in the cases of the scalar,
Dirac and gauge fields for arbitrary values of the dimension N.Comment: The case of gauge fields was added. 16 page
Terahertz Diagnostic for the Advanced Photon Source Particle Accumulator Ring
Terahertz Diagnostic for the Advanced Photon Source Particle Accumulator Rin
Perturbative Gravity in the Causal Approach
Quantum theory of the gravitation in the causal approach is studied up to the
second order of perturbation theory. We prove gauge invariance and
renormalizability in the second order of perturbation theory for the pure
gravity system (massless and massive). Then we investigate the interaction of
massless gravity with matter (described by scalars and spinors) and massless
Yang-Mills fields. We obtain a difference with respect to the classical field
theory due to the fact that in quantum field theory one cannot enforce the
divergenceless property on the vector potential and this spoils the
divergenceless property of the usual energy-momentum tensor. To correct this
one needs a supplementary ghost term in the interaction Lagrangian.Comment: 50 pages, no figures, some changes in the last sectio
Infra-Red Asymptotic Dynamics of Gauge Invariant Charged Fields: QED versus QCD
The freedom one has in constructing locally gauge invariant charged fields in
gauge theories is analyzed in full detail and exploited to construct, in QED,
an electron field whose two-point function W(p), up to the fourth order in the
coupling constant, is normalized with on-shell normalization conditions and is,
nonetheless, infra-red finite; as a consequence the radiative corrections
vanish on the mass shell and the free field singularity is
dominant, although, in contrast to quantum field theories with mass gap, the
eigenvalue of the mass operator is not isolated. The same construction,
carried out for the quark in QCD, is not sufficient for cancellation of
infra-red divergences to take place in the fourth order. The latter
divergences, however, satisfy a simple factorization equation. We speculate on
the scenario that could be drawn about infra-red asymptotic dynamics of QCD,
should this factorization equation be true in any order of perturbation theory.Comment: 30 pages, RevTex, 8 figures included using graphic
Analytic properties of high energy production amplitudes in N=4 SUSY
We investigate analytic properties of the six point planar amplitude in N=4
SUSY at the multi-Regge kinematics for final state particles. For inelastic
processes the Steinmann relations play an important role because they give a
possibility to fix the phase structure of the Regge pole and Mandelstam cut
contributions. These contributions have the Moebius invariant form in the
transverse momentum subspace. The analyticity and factorization constraints
allow us to reproduce the two-loop correction to the 6-point BDS amplitude in
N=4 SUSY obtained earlier in the leading logarithmic approximation with the use
of the s-channel unitarity. The exponentiation hypothesis for the remainder
function in the multi-Regge kinematics is also investigated. The 6-point
amplitude in LLA can be completely reproduced from the BDS ansatz with the use
of the analyticity and Regge factorization.Comment: To appear in the proceedings of 16th International Seminar on High
Energy Physics, QUARKS-2010, Kolomna, Russia, 6-12 June, 2010. 15 page
Causal Perturbation Theory and Differential Renormalization
In Causal Perturbation Theory the process of renormalization is precisely
equivalent to the extension of time ordered distributions to coincident points.
This is achieved by a modified Taylor subtraction on the corresponding test
functions. I show that the pullback of this operation to the distributions
yields expressions known from Differential Renormalization. The subtraction is
equivalent to BPHZ subtraction in momentum space. Some examples from Euclidean
scalar field theory in flat and curved spacetime will be presented.Comment: 15 pages, AMS-LaTeX, feynm
Axiomatic formulations of nonlocal and noncommutative field theories
We analyze functional analytic aspects of axiomatic formulations of nonlocal
and noncommutative quantum field theories. In particular, we completely clarify
the relation between the asymptotic commutativity condition, which ensures the
CPT symmetry and the standard spin-statistics relation for nonlocal fields, and
the regularity properties of the retarded Green's functions in momentum space
that are required for constructing a scattering theory and deriving reduction
formulas. This result is based on a relevant Paley-Wiener-Schwartz-type theorem
for analytic functionals. We also discuss the possibility of using analytic
test functions to extend the Wightman axioms to noncommutative field theory,
where the causal structure with the light cone is replaced by that with the
light wedge. We explain some essential peculiarities of deriving the CPT and
spin-statistics theorems in this enlarged framework.Comment: LaTeX, 13 pages, no figure
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