1,668 research outputs found
Strong CP breaking and quark-antiquark repulsion in QCD, at finite theta
This work is devoted to the study of the CP-breaking dynamics in QCD, at
finite theta-angle. By working in the semi-classical limit, in which the
topology of the vacuum is clustered around instantons and anti-instantons, we
show that quantum fluctuations of the theta-vacuum generate an effective
flavor-dependent repulsion between matter and anti-matter, inside hadrons. As a
consequence, during the tunneling between the degenerate vacua, quarks and
anti-quarks in the neutron migrate in opposite directions, giving rise to an
oscillating electric dipole moment. We discuss a possible phenomenological
implication of this effect.Comment: Final version, accepted for publication on Phys. Rev. D (Rapid Comm.
Quarks and Anomalies
A nonperturbative understanding of neutral pion decay was an essential step
towards the idea that strong interactions are governed by a color gauge theory
for quarks. Some aspects of this work and related problems are still important.Comment: 18 pages, 2 figures. Contribution to "50 Years of Quarks", ed. H.
Fritzsch and M. Gell-Mann, World Scientific (to be published
The Bosonic Structure of Fermions
We bosonize fermions by identifying their occupation numbers as the binary
digits of a Bose occupation number. Unlike other schemes, our method allows
infinitely many fermionic oscillators to be constructed from just one bosonic
oscillator.Comment: 7pages, ADP-94-13/T15
Status of Chiral-Scale Perturbation Theory
Chiral-scale perturbation theory PT has been proposed as an
alternative to chiral perturbation theory which
explains the rule for kaon decays. It is based on a low-energy
expansion about an infrared fixed point in three-flavor QCD. In
PT, quark condensation induces nine Nambu-Goldstone bosons: and a QCD dilaton
which we identify with the resonance. Partial conservation
of the dilatation and chiral currents constrains low-energy constants which
enter the effective Lagrangian of PT. These constraints allow us
to obtain new phenomenological bounds on the dilaton decay constant via the
coupling of to pions, whose value is known precisely from
dispersive analyses of scattering. Improved predictions for and the coupling are also noted. To test
PT for kaon decays, we revive a 1985 proposal for lattice
methods to be applied to on-shell.Comment: 10 pages, 1 figure. Presented at the 8th International Workshop on
Chiral Dynamics, 29 June 2015 - 03 July 2015, Pisa, Italy. Revision:
references and comment adde
Greater magnocellular saccadic suppression in high versus low autistic tendency suggests a causal path to local perceptual style.
Saccadic suppression-the reduction of visual sensitivity during rapid eye movements-has previously been proposed to reflect a specific suppression of the magnocellular visual system, with the initial neural site of that suppression at or prior to afferent visual information reaching striate cortex. Dysfunction in the magnocellular visual pathway has also been associated with perceptual and physiological anomalies in individuals with autism spectrum disorder or high autistic tendency, leading us to question whether saccadic suppression is altered in the broader autism phenotype. Here we show that individuals with high autistic tendency show greater saccadic suppression of low versus high spatial frequency gratings while those with low autistic tendency do not. In addition, those with high but not low autism spectrum quotient (AQ) demonstrated pre-cortical (35-45 ms) evoked potential differences (saccade versus fixation) to a large, low contrast, pseudo-randomly flashing bar. Both AQ groups showed similar differential visual evoked potential effects in later epochs (80-160 ms) at high contrast. Thus, the magnocellular theory of saccadic suppression appears untenable as a general description for the typically developing population. Our results also suggest that the bias towards local perceptual style reported in autism may be due to selective suppression of low spatial frequency information accompanying every saccadic eye movement
Electromagnetic Contributions to the Schiff Moment
The Schiff moment, \smij, is a parity and time reversal violating
fermion-fermion coupling. The nucleus-electron Schiff moment generically gives
the most important contribution to the electric dipole moments of atoms and
molecules with zero net intrinsic electronic spin and nuclear spin . Here, the electromagnetic contribution to the Schiff moment, \emij, is
considered. For a nucleon, the leading chirally violating contribution to this
interaction is calculable in the chiral limit in terms of the parity and time
reversal violating pion-nucleon coupling. For the Schiff moment of heavy
nuclei, this chiral contribution is somewhat smaller than the finite size
effect discussed previously in the literature.Comment: 7 pages, 1 figure (not included), Tex file, requires phyzzx, preprint
SCIPP 93/4
Strong CP, Up-Quark Mass, and the Randall-Sundrum Microscope
In the Randall-Sundrum model, setting the ratio of up and down quark masses
, relevant to the strong CP problem, does not require chiral
symmetry or fine-tuning, due to exponential bulk fermion profiles. We point out
that such geometric suppression of the mass of a fermion magnifies the masses
of its corresponding Kaluza-Klein (KK) states. In this sense, these KK states
act as "microscopes" for probing light quark and lepton masses. In simple
realizations, this hypothesis can be testable at future colliders, like the
LHC, by measuring the spectrum of level-1 KK fermions. The microscope can then
provide an experimental test for the vanishing of in the ultraviolet,
independently of non-perturbative determinations, by lattice simulations or
other means, at hadronic scales. We also briefly comment on application of our
microscope idea to other fermions, such as the electron and neutrinos.Comment: 7 pages. New discussions and references added. Main previous
conclusions unchange
Chiral perturbation theory in a theta vacuum
We consider chiral perturbation theory (ChPT) with a non-zero theta term. Due
to the CP violating term, the vacuum of chiral fields is shifted to a
non-trivial element on the SU(N_f) group manifold. The CP violation also
provides mixing of different CP eigenstates, between scalar and pseudoscalar,
or vector and axialvector operators. We investigate upto O(theta^2) effects on
the mesonic two point correlators of ChPT to the one-loop order. We also
address the effects of fixing topology, by using saddle point integration in
the Fourier transform with respect to theta.Comment: 31 pages, references added, minor corrections, version published in
PR
The electric dipole form factor of the nucleon
The electric dipole form factor of the nucleon stemming from the QCD
term is calculated in chiral perturbation theory in leading
order. To this order, the form factor originates from the pion cloud. Its
momentum-dependence is proportional to a non-derivative time-reversal-violating
pion-nucleon coupling, and the scale for momentum variation--appearing, in
particular, in the radius of the form factor--is the pion mass.Comment: 8 pages, 2 figure
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