4,062 research outputs found
Effective potential in Lorentz-breaking field theory models
We calculate explicitly the one-loop effective potential in different
Lorentz-breaking field theory models. First, we consider a Yukawa-like theory
and, then, some examples of Lorentz-violating extensions of scalar QED. We
observed, for the extended QED models, that the resulting effective potential
converges to the known result in the limit in which Lorentz-symmetry is
restored. Besides, the one-loop corrections to the effective potential in all
the cases we studied depend on the background tensors responsible for the
Lorentz symmetry violation. This have consequences in physical quantities like,
for example, in the induced mass due to Coleman-Weinberg mechanism.Comment: Version accepted for publication in EPJ
Optimized Effective Potentials in Finite Basis Sets
The finite basis optimized effective potential (OEP) method within density
functional theory is examined as an ill-posed problem. It is shown that the
generation of nonphysical potentials is a controllable manifestation of the use
of unbalanced, and thus unsuitable, basis sets. A modified functional
incorporating a regularizing smoothness measure of the OEP is introduced. This
provides a condition on balanced basis sets for the potential, as well as a
method to determine the most appropriate OEP potential and energy from
calculations performed with any finite basis set.Comment: 23 pages, 28 figure
Constraining multi-Higgs flavour models
To study a flavour model with a non-minimal Higgs sector one must first
define the symmetries of the fields; then identify what types of vacua exist
and how they may break the symmetries; and finally determine whether the
remnant symmetries are compatible with the experimental data. Here we address
all these issues in the context of flavour models with any number of Higgs
doublets. We stress the importance of analysing the Higgs vacuum expectation
values that are pseudo-invariant under the generators of all subgroups. It is
shown that the only way of obtaining a physical CKM mixing matrix and,
simultaneously, non-degenerate and non-zero quark masses is requiring the
vacuum expectation values of the Higgs fields to break completely the full
flavour group, except possibly for some symmetry belonging to baryon number.
The application of this technique to some illustrative examples, such as the
flavour groups Delta(27), A4 and S3, is also presented.Comment: 13 pages, 3 figures, title and abstract changed, comments and
references added; matches version to appear in The European Physical Journal
q-Supersymmetric Generalization of von Neumann's Theorem
Assuming that there exist operators which form an irreducible representation
of the q-superoscillator algebra, it is proved that any two such
representations are equivalent, related by a uniquely determined superunitary
transformation. This provides with a q-supersymmetric generalization of the
well-known uniqueness theorem of von Neumann for any finite number of degrees
of freedom.Comment: 10 pages, Latex, HU-TFT-93-2
The full Lorentz-violating vacuum polarization tensor: low and high energy limits
We compute the full vacuum polarization tensor in the fermion sector of
Lorentz-violating QED. Even if we assume momentum routing invariance of the
Feynman diagrams, it is not possible to fix all surface terms and find an
unambiguity free vacuum polarization tensor. The high and low energy limits of
this tensor is presented. In the high energy limit, only
coeffcients contribute. In the low energy limit, we fnd that Lorentz-violating
induced terms depend only on , and
coeffcients and they are suppressed by powers of . This
limit allows to obtain implications for condensed matter systems, explicitly,
for the Hall effect in Weyl semimetals.Comment: 11 pages, 4 figure
Advances towards the systematization of calculations with Implicit Regularization
There is currently a high demand for theoretical predictions for processes at
next-to-next-to-leading order (NNLO) and beyond, mainly due to the large amount
of data which has already been collected at LHC. This requires practical
methods that meet the physical requirements of the models under study. We
develop a new procedure for applying Constrained Implicit Regularization which
simplifies the calculation of amplitudes, including finite parts. The algebraic
identities to separate the divergent parts free from the external momenta are
used after the Feynman parametrization. These algebraic identities establish a
set of scale relations which are always the same and do not need to be
calculated in each situation. This procedure unifies the calculations in
massive and non-massive models in an unique procedure. We establish a
systematization of the calculation of one-loop amplitudes and extend the
procedure for higher-loop orders.Comment: 25 pages, 4 figure
Chirally symmetric quark description of low energy \pi-\pi scattering
Weinberg's theorem for \pi-\pi scattering, including the Adler zero at
threshold in the chiral limit, is analytically proved for microscopic quark
models that preserve chiral symmetry. Implementing Ward-Takahashi identities,
the isospin 0 and 2 scattering lengths are derived in exact agreement with
Weinberg's low energy results. Our proof applies to alternative quark
formulations including the Hamiltonian and Euclidean space Dyson-Schwinger
approaches. Finally, the threshold \pi-\pi scattering amplitudes are calculated
using the Dyson-Schwinger equations in the rainbow-ladder truncation,
confirming the formal derivation.Comment: 10 pages, 7 figures, Revtex
Stability window and mass-radius relation for magnetized strange quark stars
The stability of magnetized strange quark matter (MSQM) is investigated
within the phenomenological MIT bag model, taking into account the variation of
the relevant input parameters, namely, the strange quark mass, baryon density,
magnetic field and bag parameter. We obtain that the energy per baryon
decreases as the magnetic field increases, and its minimum value at vanishing
pressure is lower than the value found for SQM. This implies that MSQM is more
stable than non-magnetized SQM. Furthermore, the stability window of MSQM is
found to be wider than the corresponding one of SQM. The mass-radius relation
for magnetized strange quark stars is also derived in this framework.Comment: 12 pages, 6 figures, 3 table
GoCo: planning expressive commitment protocols
Acknowledgements We gratefully thank those who shared their code with us. Special thanks to Ugur Kuter. We thank the anonymous reviewers, and also acknowledge with gratitude the reviewers at ProMASâ11, AAMASâ13, AAAIâ13, and AAMASâ15, where preliminary parts of this work appeared. FM thanks the Conselho Nacional de Desenvolvimento CientĂfico e TecnolĂłgico (CNPq) for the support within process numbers 306864/2013-4 under the PQ fellowship and 482156/2013-9 under the Universal project programs. NYS acknowledges support of the AUB University Research Board Grant Number 102853 and the OSB Grant OFFER_C1_2013_2014.Peer reviewe
Higher-order one-loop contributions in Lorentz-breaking QED
We calculate higher-order quantum contributions in different
Lorentz-violating parameters to the gauge sector of the extended QED. As a
result of this one-loop calculation, some terms which do not produce
first-order corrections, contribute with nontrivial gauge-invariant
second-order quantum inductions.Comment: 10 page
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