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

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 ${1 \over 2}$. 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

Status of Chiral-Scale Perturbation Theory

Chiral-scale perturbation theory $\chi$PT$_\sigma$ has been proposed as an alternative to chiral $SU(3)_L\times SU(3)_R$ perturbation theory which explains the $\Delta I = 1/2$ rule for kaon decays. It is based on a low-energy expansion about an infrared fixed point in three-flavor QCD. In $\chi$PT$_\sigma$, quark condensation $\langle\bar q q \rangle_\mathrm{vac} \neq 0$ induces nine Nambu-Goldstone bosons: $\pi, K, \eta$ and a QCD dilaton $\sigma$ which we identify with the $f_0(500)$ resonance. Partial conservation of the dilatation and chiral currents constrains low-energy constants which enter the effective Lagrangian of $\chi$PT$_\sigma$. These constraints allow us to obtain new phenomenological bounds on the dilaton decay constant via the coupling of $\sigma/f_0$ to pions, whose value is known precisely from dispersive analyses of $\pi\pi$ scattering. Improved predictions for $\sigma \to \gamma \gamma$ and the $\sigma NN$ coupling are also noted. To test $\chi$PT$_\sigma$ for kaon decays, we revive a 1985 proposal for lattice methods to be applied to $K \to \pi$ 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

Strong CP, Up-Quark Mass, and the Randall-Sundrum Microscope

In the Randall-Sundrum model, setting the ratio of up and down quark masses $m_u/m_d << 1$, 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 $m_u$ 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

Surround-Masking Affects Visual Estimation Ability

Visual estimation of numerosity involves the discrimination of magnitude between two distributions or perceptual sets that vary in number of elements. How performance on such estimation depends on peripheral sensory stimulation is unclear, even in typically developing adults. Here, we varied the central and surround contrast of stimuli that comprised a visual estimation task in order to determine whether mechanisms involved with the removal of unessential visual input functionally contributes toward number acuity. The visual estimation judgments of typically developed adults were significantly impaired for high but not low contrast surround stimulus conditions. The center and surround contrasts of the stimuli also differentially affected the accuracy of numerosity estimation depending on whether fewer or more dots were presented. Remarkably, observers demonstrated the highest mean percentage accuracy across stimulus conditions in the discrimination of more elements when the surround contrast was low and the background luminance of the central region containing the elements was dark (black center). Conversely, accuracy was severely impaired during the discrimination of fewer elements when the surround contrast was high and the background luminance of the central region was mid level (gray center). These findings suggest that estimation ability is functionally related to the quality of low-order filtration of unessential visual information. These surround masking results may help understanding of the poor visual estimation ability commonly observed in developmental dyscalculia

Heavy-quark axial charges to non-leading order

We combine Witten's renormalization group with the matching conditions of Bernreuther and Wetzel to calculate at next-to-leading order the complete heavy-quark contribution to the neutral-current axial-charge measurable in neutrino-proton elastic scattering. Our results are manifestly renormalization group invariant.Comment: 5 pages, revtex styl