Search

Baryonic states are sufficiently complex to reveal physics that is hidden in the mesonic bound states. Using gauge/gravity correspondence we study analytically and numerically baryons in theories with space-dependent $\theta$-term, or theories under strong magnetic fields. Such holographic studies on baryons are accommodated in a generic analytic framework we develop for anisotropic theories, where their qualitative features are common irrespective of the source that triggers the anisotropy. We find that the distribution of the quarks forming the state, depends on the angle between the baryon and the anisotropic direction. Its shape is increasingly elliptic with respect to the strength of the field sourcing the anisotropy, counterbalancing the broken rotational invariance on the gluonic degrees of freedom. Strikingly, the baryons dissociate in stages with a process that depends on the proximity of the quarks to the anisotropic direction, where certain quark pairs abandon the bound state first, followed by the closest pairs to them as the temperature increases. This observation may also serve as a way to identify the nature of certain exotic states. Finally, we investigate holographic baryons with decreased number of quarks and explain why in theories under consideration the presence of anisotropy does not modify the universal stability condition in contrast to the usual trend., Comment: 37 pages, 12 figures; v2 minor improvements, references added

Possibilities to test the Lorentz invariance of the weak interaction in muon decay are considered. We derive the direction-dependent muon-decay rate with a general Lorentz-violating addition to the W-boson propagator. We discuss measurements of the directional and boost dependence of the Michel parameters and of the muon lifetime as a function of absolute velocity. The total muon-decay rate in the Lorentz-violating standard model extension is addressed. Suggestions are made for dedicated (re) analyses of the pertinent data and for future experiments. Dutch Stichting voor Fundamenteel Onderzoek der Materie (FOM) under Programmes 104 and 114 and project 08PR2636

We present a study of $U(1)$ gauged modification of the $2+1$-dimensional planar Skyrme model with a particular choice of the symmetry breaking potential term which combines a short-range repulsion and a long-range attraction. In the absence of the gauge interaction, the multisolitons of the model are aloof, as they consist of the individual constituents which are well separated. A peculiar feature of the model is that there are usually several different stable static multisoliton solutions of rather similar energy in a topological sector of given degree. We investigate the pattern of the solutions and find new previously unknown local minima. It is shown that coupling of the aloof planar multi-Skyrmions to the magnetic field strongly affects the pattern of interaction between the constituents. We analyze the dependency of the structure of the solutions, their energies, and magnetic fluxes on the strength of the gauge coupling. It is found that, generically, in the strong coupling limit, the coupling to the gauge field results in effective recovery of the rotational invariance of the configuration.

We show that inflationary models with broken rotational invariance generate testable off-diagonal signatures in the correlation between the $\mu$-type distortion and temperature fluctuations of the cosmic microwave background. More precisely, scenarios with a quadrupolar bispectrum asymmetry, usually generated by fluctuations of primordial vector fields, produce a nonvanishing $\mu$-$T$ correlation when $|\ell_1-\ell_2|=2$. Since spectral distortions are sensitive to primordial fluctuations up to very small scales, a cosmic variance limited spectral distortion experiment can detect such effects with a high signal-to-noise ratio., Comment: 9 pages, 3 figures. Accepted for publication in PRD

In this work, we study the radiative generation of the Lorentz-violating Euler-Heisenberg action, in the weak field approximation. For this, we first consider a nonperturbative calculation in the coefficient $c_{\mu\nu}$, however, by assuming rotational invariance. Within this approach, we also obtain the results of the amplitude for the photon triple splitting. In the following, we take into account the perturbative approach, where $c_{\mu\nu}$ is treated as a insertion in the propagator and a new vertex. The partial results are in fact an expansion up to first order in $c_{\mu\nu}$ of the nonperturbative ones, with $c_{00}=\kappa$ and $c_{0i}=c_{ij}=0$. This suggest that the complete results obtained in the nonperturbative approach can be used in both treatments., Comment: 15 pages, 5 figures, accepted for publication in Phys. Rev. D

A new test of Lorentz invariance in the weak interactions has been made by searching for variations in the decay rate of spin-polarized 20Na nuclei. This test is unique to Gamow-Teller transitions, as was shown in the framework of a recently developed theory that assumes a Lorentz symmetry breaking background field of tensor nature. The nuclear spins were polarized in the up and down direction, putting a limit on the amplitude of sidereal variations of the form |(\Gamma_{up} - \Gamma_{down})| / (\Gamma_{up} + \Gamma_{down}) < 3 * 10^{-3}. This measurement shows a possible route toward a more detailed testing of Lorentz symmetry in weak interactions., Comment: 11 pages, 6 figures

In the light-front form of field theory, boost invariance is a manifest symmetry. On the down side, parity and rotational invariance are not manifest, leaving the possibility that approximations or incorrect renormalization might lead to violations of these symmetries for physical observables. In this paper, it is discussed how one can turn this deficiency into an advantage and utilize parity violations (or the absence thereof) in practice for constraining effective light-front Hamiltonians. More precisely, we will identify observables that are both sensitive to parity violations and easily calculable numerically in a nonperturbative framework and we will use these observables to constrain the finite part of noncovariant counterterms in effective light-front Hamiltonians. {copyright} {ital 1996 The American Physical Society.}

Rotational invariance is violated in the light-cone quantization method when the Fock space is truncated for practical calculations. To what extent the rotation symmetry is broken in the light-cone quantization approach can be quantified by calculating the explicit rotation dependence of the two-body scattering phase shifts. We analyze the scattering phase shifts in a simple scalar field model, extending the light-cone ladder approximation to the lowest order light-cone Tamm-Dancoff approximation in which the self-energy corrections are incorporated. We find that the self-energy effects significantly restore the rotation symmetry. Also, these effects make the phase shifts stabilize as the coupling constant grows. This is in a good agreement with the previous bound state results that the self-energy effects are as repulsive as relativistic kinematic corrections and retardation effects.

Without assuming rotational invariance, we derive Bogomol'nyi equations for the solitons in the abelian Chern-Simons gauge theories with the anomalous magnetic moment interaction. We also evaluate the number of zero modes around a static soliton configuration., 9 pages, Revtex, SNUTP-94/65

We study the one-component ${\ensuremath{\Phi}}^{4}$ model for four different lattice actions in the Gaussian limit and for the Ising model in the broken phase with a Monte Carlo simulation. Emphasis is put on the Euclidean invariance properties of the boson propagator. A measure of the violation of rotational symmetry is used to compare the regularization dependence of the triviality bound.

The analysis of the light-cone two-body bound-state equation is extended to the scattering problem. The rotational invariance is violated in the light-cone quantization method when the Fock space is truncated for practical calculations. Using a simple scalar field model, we investigate the explicit rotation dependence of the two-body scattering phase shifts in the light-cone quantization approach. We find the regions of coupling constant and c.m. momentum where the rotation dependence in the phase shift is negligible. We also make a connection of our analysis with the light-cone scattering formalism recently presented by Fuda

In the study of the decay of a heavy scalar particle at rest in the Yukawa model at the one- and two-loop levels, it is shown explicitly that naive light-cone quantization leads to a violation of rotational invariance. Noncovariant counterterms are constructed in detail to restore Lorentz covariance. An analysis of surface and zero-mode contributions clarifies the origin of the problem.

I have performed scaling tests using quenched spectroscopy of a family of fermion actions which have a hypercubic kinetic term, gauge connections built of smeared links, and an anomalous magnetic moment term. These actions show improved rotational invariance compared to the standard Wilson action and to the tadpole-improved clover action. Hyperfine splittings are improved compared to the standard Wilson action (at the level of a factor of three in the lattice spacing), and are about the same as for the tadpole-improved clover action., 30 pages, LaTeX, 16 figures, uses epsf

In analogy with the extension of electromagnetism by the inclusion of the Dirac monopole, the possibility of extending the Yang-Mills formalism to include two separate types of self-coupling for the vector field is examined. A local Lagrangian which lacks manifest rotational invariance is presented.

A solvable model of an apparatus for measuring a spin component of a spin-1/2 particle is considered. The model enjoys full rotational invariance and, in the limit case in which a part of the apparatus becomes infinitely massive, works according to the ideal measurement scheme. The model is applied to the study of the deviations from the ideal measurement scheme imposed by the conservation of angular momentum. The detailed analysis of the model allows one to calculate the size of the various nonideal terms in the measurement scheme and to understand the physical mechanism which gives rise to such terms.

A search was made for a departure from rotational symmetry in the angular distribution of $\ensuremath{\beta}$-decay electrons, similar to the search recently reported by Newman and Wiesner. The apparatus rotated with the earth and measured the electron counting rate as a function of $\ensuremath{\theta}$, the angle between the vernal equinox and the electrons' momentum vector. Geometry and source thickness were chosen to give small attenuations to variations of the form $cos\ensuremath{\theta}$ or $cos2\ensuremath{\theta}$. Sources used were first-forbidden $^{137}\mathrm{Cs}$ and second-forbidden $^{99}\mathrm{Tc}$, improving sensitivity to any effect violating the usual angular momentum selection rules. No departure from rotational symmetry was seen; an upper limit of 3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$ was set for the amplitude of either a $cos\ensuremath{\theta}$ or $cos2\ensuremath{\theta}$ variation for either source.

It is shown on an example that sensitive tests of the isotropy of space (i.e., of rotation invariance) in strong-interaction particle reactions are almost identical to tests of parity conservation, and hence the two can be confused without some additional experiments which we specify.

Rotations by $2\ensuremath{\pi}$ radians of spin-\textonehalf{} systems are predicted to give rise to factors of -1 in the wave function. We propose an experiment involving Fresnel diffraction of thermal neutrons to test this proposition.

We investigate magnetic-monopole-type theories, including those where the gauge field acquires a mass. The study is based on a modification of Zwanziger's local Lagrangian formulation of the usual (zero-mass) theory. The quantization is carried out by using Dirac's general method. For the mass-zero case the known results are recovered including the charge-quantization condition. The Hamiltonian and angular momentum for the massive case are derived and discussed. Further, it is shown how Nambu's static phenomenological Hamiltonian can be derived as a special case of the massive theory. Certain difficulties associated with the rotational invariance of such theories are pointed out.

We consider the possibility that the weak interaction might recognize a preferred direction in space. We report a search for anisotropy in the $\ensuremath{\beta}$ decay of unpolarized $^{90}\mathrm{Y}$ nuclei. Our result may be expressed in terms of an expansion of the angular distribution of the decay electron: $\ensuremath{\Gamma}(\ensuremath{\theta})\ensuremath{\propto}1+{\ensuremath{\epsilon}}_{1}cos\ensuremath{\theta}+{\ensuremath{\epsilon}}_{2}{cos}^{2}\ensuremath{\theta}+\ensuremath{\cdots}$, where $\ensuremath{\theta}$ is the angle between the direction of emission of the electron and any supposed asymmetry axis. We find for any axis that $|{\ensuremath{\epsilon}}_{1}|l{10}^{\ensuremath{-}6.8}$ and $|{\ensuremath{\epsilon}}_{2}|l{10}^{\ensuremath{-}5.7}$ (90% confidence limits).

We extend the previously developed one-dimensional causal theory of tachyons to three dimensions. The result is a three-dimensional theory of interacting tachyons in which coordinates in reference frames with subluminal relative velocity are related by the Lorentz transformations, and in which no paradoxes involving causal loops can arise. The resulting theory involves a preferred spatial direction and preferred velocity perpendicular to that direction, so that physical laws governing tachyons are not invariant under rotations or proper Lorentz transformations. This lack of invariance should manifest itself even in processes involving only bradyons, to the extent that coupling to virtual tachyons is important. We discuss the limits which experimental evidence on the validity of rotational invariance places on tachyon couplings in the theory and possible additional experiments for searching for lack of such invariance. In general the limits which existing evidence for rotational invariance places on tachyon couplings in our theory are much less stringent than the very low limits on tachyon coupling strengths which were obtained in a recent experimental analysis of Danburg and Kalbfleisch; we propose a possible mechanism which might allow tachyon couplings of a reasonable magnitude without producing observable effects in the experiments considered by these authors.

The hadron Hamiltonian for strong and nonleptonic weak interactions is regarded as a function of the Cabibbo angle, evolving from a primitive''initial condition'' (in which weak and strong hypercharge are identical) to its physical value by a rotation projection. Various existing determninations of the Cabibbe angle are reproduced and a new one is calculated, with good numerical results for an initial condition in which chiral SU(2) is broken only by an octet term in the electromagnetic direction. (auth)

It is shown that the photon spin is associated with the rotational invariance in a two-dimensional space spanned by the two "translation" parameters of the E(2)-like little group of the Poincar\'e group. Since the translation in the E(2)-like space is a gauge transformation, the photon spin can be associated with an orbitlike rotation with nonzero radius in the gauge space.