10 research outputs found
Baryogenesis, Dark Matter and the Pentagon
We present a new mechanism for baryogenesis, which links the baryon asymmetry
of the universe to the dark matter density. The mechanism arises naturally in
the Pentagon model of TeV scale physics. In that context, it forces a
re-evaluation of some of the assumptions of the model, and we detail the
changes that are required in order to fit observations.Comment: JHEP3 LaTeX, 15 pages. New version corrects errors in the electroweak
baryon violating and matter radiation temperatures, which were pointed out by
the referee. Substantial quantitative but no qualitative change to our
conclusion
Effects of Squark Processes on the Axino CDM Abundance
We investigate the role of an effective dimension-4 axino-quark-squark
coupling in the thermal processes producing stable cold axino relics in the
early Universe. We find that, while the induced squark and quark scattering
processes are always negligible, squark decays become important in the case of
low reheat temperature and large gluino mass. The effect can tighten the bounds
on the scenario from the requirement that cold dark matter axinos do not
overclose the Universe.Comment: 20 pages, 9 figures, uses JHEP3.cl
Confusing the extragalactic neutrino flux limit with a neutrino propagation limit
We study the possible suppression of the extragalactic neutrino flux due to a
nonstandard interaction during its propagation. In particular, we study
neutrino interaction with an ultra-light scalar field dark matter. It is shown
that the extragalactic neutrino flux may be suppressed by such an interaction,
leading to a new mechanism to reduce the ultra-high energy neutrino flux. We
study both the cases of non-self-conjugate as well as self-conjugate dark
matter. In the first case, the suppression is independent of the neutrino and
dark matter masses. We conclude that care must be taken when explaining limits
on the neutrino flux through source acceleration mechanisms only, since there
could be other mechanisms for the reduction of the neutrino flux.Comment: 15 pages, 4 figures. Important changes implemented. Abstract
modified. Conclusions remain. To be published in JCA
Pion light-cone wave function and pion distribution amplitude in the Nambu-Jona-Lasinio model
We compute the pion light-cone wave function and the pion quark distribution
amplitude in the Nambu-Jona-Lasinio model. We use the Pauli-Villars
regularization method and as a result the distribution amplitude satisfies
proper normalization and crossing properties. In the chiral limit we obtain the
simple results, namely phi_pi(x)=1 for the pion distribution amplitude, and
= -M / f_pi^2 for the second moment of the pion light-cone
wave function, where M is the constituent quark mass and f_pi is the pion decay
constant. After the QCD Gegenbauer evolution of the pion distribution amplitude
good end-point behavior is recovered, and a satisfactory agreement with the
analysis of the experimental data from CLEO is achieved. This allows us to
determine the momentum scale corresponding to our model calculation, which is
close to the value Q_0 = 313 MeV obtained earlier from the analogous analysis
of the pion parton distribution function. The value of is, after the
QCD evolution, around (400 MeV)^2. In addition, the model predicts a linear
integral relation between the pion distribution amplitude and the parton
distribution function of the pion, which holds at the leading-order QCD
evolution.Comment: mistake in Eq.(38) correcte
Spectral quark model and low-energy hadron phenomenology
We propose a spectral quark model which can be applied to low energy hadronic
physics. The approach is based on a generalization of the Lehmann
representation of the quark propagator. We work at the one-quark-loop level.
Electromagnetic and chiral invariance are ensured with help of the gauge
technique which provides particular solutions to the Ward-Takahashi identities.
General conditions on the quark spectral function follow from natural physical
requirements. In particular, the function is normalized, its all positive
moments must vanish, while the physical observables depend on negative moments
and the so-called log-moments. As a consequence, the model is made finite,
dispersion relations hold, chiral anomalies are preserved, and the twist
expansion is free from logarithmic scaling violations, as requested of a
low-energy model. We study a variety of processes and show that the framework
is very simple and practical. Finally, incorporating the idea of vector-meson
dominance, we present an explicit construction of the quark spectral function
which satisfies all the requirements. The corresponding momentum representation
of the resulting quark propagator exhibits only cuts on the physical axis, with
no poles present anywhere in the complex momentum space. The momentum-dependent
quark mass compares very well to recent lattice calculations. A large number of
predictions and relations can be deduced from our approach for such quantities
as the pion light-cone wave function, non-local quark condensate, pion
transition form factor, pion valence parton distribution function, etc.Comment: revtex, 24 pages, 3 figure
Confinement and Chiral Symmetry Breaking via Domain-Like Structures in the QCD Vacuum
A qualitative mechanism for the emergence of domain structured background
gluon fields due to singularities in gauge field configurations is considered,
and a model displaying a type of mean field approximation to the QCD partition
function based on this mechanism is formulated. Estimation of the vacuum
parameters (gluon condensate, topological susceptibility, string constant and
quark condensate) indicates that domain-like structures lead to an area law for
the Wilson loop, nonzero topological susceptibility and spontaneous breakdown
of chiral symmetry. Gluon and ghost propagators in the presence of domains are
calculated explicitly and their analytical properties are discussed. The
Fourier transforms of the propagators are entire functions and thus describe
confined dynamical fields.Comment: RevTeX, 48 pages (32 pages + Appendices A-E), new references added
[1,2,4,5] and minor formulae corrected for typographical error
Vacuum condensates and the pion wave functions in the nonlocal chiral model
We use the simple instanton motivated Nambu Jona-Lasinio - type model to
calculate a twist 3 pseudoscalar pion light cone wave function. Using
normalisation condition for this wave function we calculate the quark
condensate and also the gluon condensate, which agree with the phenomenological
values for these quantities. Since we can compute also the k_T^2 dependence of
the light cone wave functions, we calculate k_T^2 moments of the pseudo-scalar
and axial-vector wave functions which are related to the mixed vacuum
condensates. This allows us to extract the condensates and compare them with
existing estimates.Comment: 12 pages, 7 figures; three new paragraphs added: one (in sec. IV)
discusses the relation between quark and gluon condensates, the other two (in
secs. I and VI) clarify the difference between the normalisation scale Q_0,
at which the condensates are evaluated, and the model parameter Lambda; new
references added; to be published in Phys. Rev.
Fermionic current induced by magnetic flux in compactified cosmic string spacetime
In this paper, we investigate the fermionic current densities induced by a
magnetic flux running along the idealized cosmic string in a four-dimensional
spacetime, admitting that the coordinate along the string's axis is
compactified. In order to develop this investigation we construct the complete
set of fermionic mode functions obeying a general quasiperiodicity condition
along the compactified dimension. The vacuum expectation value of the azimuthal
current density is decomposed into two parts. The first one corresponds to the
uncompactified cosmic string geometry and the second one is the correction
induced by the compactification. For the first part we provide a closed
expression which includes various special cases previously discussed in the
literature. The second part is an odd periodic function of the magnetic flux
along the string axis with the period equal to the flux quantum and it is an
even function of the magnetic flux enclosed by the string axis. The
compactification of the cosmic string axis in combination with the
quasiperiodicity condition leads to the nonzero axial current density. The
latter is an even periodic function of the magnetic flux along the string axis
and an odd periodic function of the magnetic flux enclosed by the string axis.
The axial current density vanishes for untwisted and twisted fields in the
absence of the magnetic flux enclosed by the string axis. The asymptotic
behavior of the vacuum fermionic current is investigated near the string and at
large distances from it. In particular, the topological part of the azimuthal
current and the axial current are finite on the string's axis.Comment: 22 pages, 4 figure