Electric Charge Quantization

Experimentally it has been known for a long time that the electric charges of the observed particles appear to be quantized. An approach to understanding electric charge quantization that can be used for gauge theories with explicit $U(1)$ factors -- such as the standard model and its variants -- is pedagogically reviewed and discussed in this article. This approach uses the allowed invariances of the Lagrangian and their associated anomaly cancellation equations. We demonstrate that charge may be de-quantized in the three-generation standard model with massless neutrinos, because differences in family-lepton--numbers are anomaly-free. We also review the relevant experimental limits. Our approach to charge quantization suggests that the minimal standard model should be extended so that family-lepton--number differences are explicitly broken. We briefly discuss some candidate extensions (e.g. the minimal standard model augmented by Majorana right-handed neutrinos).Comment: 18 pages, LaTeX, UM-P-92/5

Sideband cooling while preserving coherences in the nuclear spin state in group-II-like atoms

We propose a method for laser cooling group-II-like atoms without changing the quantum state of their nuclear spins, thus preserving coherences that are usually destroyed by optical pumping. As group-II-like atoms have a $^1S_0$ closed-shell ground state, nuclear spin and electronic degrees of freedom are decoupled, allowing for independent manipulation. The hyperfine interaction that couples these degrees of freedom in excited states can be suppressed through the application of external magnetic fields. Our protocol employs resolved-sideband cooling on the forbidden clock transition, $^1S_0 \to {}^3P_0$, with quenching via coupling to the rapidly decaying $^1P_1$ state, deep in the Paschen-Back regime. This makes it possible to laser cool neutral atomic qubits without destroying the quantum information stored in their nuclear spins, as shown in two examples, $^{171}$Yb and $^{87}$Sr.Comment: 4 pages, 3 figures v4: minor changes in text, changes in the references, published versio

Experimental observation of the 'Tilting Mode' of an array of vortices in a dilute Bose-Einstein Condensate

We have measured the precession frequency of a vortex lattice in a Bose-Einstein condensate of 87Rb atoms. The observed mode corresponds to a collective motion in which all the vortices in the array are tilted by a small angle with respect to the z-axis (the symmetry axis of the trapping potential) and synchronously rotate about this axis. This motion corresponds to excitation of a Kelvin wave along the core of each vortex and we have verified that it has the handedness expected for such helical waves, i.e. precession in the opposite sense to the rotational flow around the vortices. The experimental method used to excite this collective mode closely resembles that used to study the scissors mode and excitation of the scissors mode for a condensate containing a vortex array was used to determine the angular momentum of the system. Indeed, the collective tilting of the array that we have observed has previously been referred to as an `anomalous' scissors mode.Comment: 5 pages, 7 figures to be published in PR

Solutions of the atmospheric, solar and LSND neutrino anomalies from TeV scale quark-lepton unification

There is a unique $SU(4) \otimes SU(2)_L \otimes SU(2)_R$ gauge model which allows quarks and leptons to be unified at the TeV scale. It is already known that the neutrino masses arise radiatively in the model and are naturally light. We study the atmospheric, solar and LSND neutrino anomalies within the framework of this model.Comment: Minor changes, 31 page

Quark-Lepton Quartification

We propose that quarks and leptons are interchangeable entities in the high-energy limit. This naturally results in the extension of [SU(3)]^3 trinification to [SU(3)]^4 quartification. In addition to the unbroken color SU(3)_q of quarks, there is now also a color SU(3)_l of leptons which reduces to an unbroken SU(2)_l. We discuss the natural occurrence of SU(2)_l doublets at the TeV energy scale, which leads remarkably to the unification of all gauge couplings without supersymmetry. Proton decay occurs through the exchange of scalar bosons, with a lifetime in the range 10^{34} - 10^{36} years.Comment: 12 pages, 4 figures. Reference adde

Active-sterile neutrino oscillations in the early Universe: asymmetry generation at low |delta m^2| and the Landau-Zener approximation

It is well established that active-sterile neutrino oscillations generate large neutrino asymmetries for very small mixing angles ($\sin^2 2\theta_0\lesssim 10^{-4}$), negative values of $\delta m^2$ and provided that $|\delta m^2|\gtrsim 10^{-4} {\rm eV^2}$. By numerically solving the quantum kinetic equations, we show that the generation still occurs at much lower values of $|\delta m^2|$. We also describe the borders of the generation at small mixing angles and show how our numerical results can be analytically understood within the framework of the Landau-Zener approximation thereby extending previous work based on the adiabatic limit. This approximate approach leads to a fair description of the MSW dominated regime of the neutrino asymmetry evolution and is also able to correctly reproduce its final value. We also briefly discuss the impact that neutrino asymmetry generation could have on big bang nucleosynthesis, CMBR and relic neutrinos.Comment: 29 pages, 8 figures; to appear on Phys. ReV. D; figure 7 added, new curves in figure 5a, new figure

Remark on the vectorlike nature of the electromagnetism and the electric charge quantization

In this work we study the structure of the electromagnetic interactions and the electric charge quantization in gauge theories of electroweak interactions based on semi-simple groups. We show that in the standard model of the electroweak interactions the structure of the electromagnetic interactions is strongly correlated to the quantization pattern of the electric charges. We examine these two questions also in all possible chiral bilepton gauge models of the electroweak interactions. In all they we can explain the vectorlike nature of the electromagnetic interactions and the electric charge quantization together demanding nonvanishing fermion masses and the anomaly cancellations.Comment: 17 pages, latex, no figure

Charginos and Neutralinos Production at 3-3-1 Supersymmetric Model in e−e−e^-e^- Scattering

The goal of this article is to derive the Feynman rules involving charginos, neutralinos, double charged gauge bosons and sleptons in a 3-3-1 supersymmetric model. Using these Feynman rules we will calculate the production of a double charged chargino with a neutralino and also the production of a pair of single charged charginos, both in an electron- electron $e^-e^-$ process.Comment: 18 pages, 8 figures, 2 table

Quasi-2D Confinement of a BEC in a Combined Optical and Magnetic Potential

We have added an optical potential to a conventional Time-averaged Orbiting Potential (TOP) trap to create a highly anisotropic hybrid trap for ultracold atoms. Axial confinement is provided by the optical potential; the maximum frequency currently obtainable in this direction is 2.2 kHz for rubidium. The radial confinement is independently controlled by the magnetic trap and can be a factor of 700 times smaller than in the axial direction. This large anisotropy is more than sufficient to confine condensates with ~10^5 atoms in a Quasi-2D (Q2D) regime, and we have verified this by measuring a change in the free expansion of the condensate; our results agree with a variational model.Comment: 11 pages, 10 figur

The Higgs Sector of the Minimal 3 3 1 Model Revisited

The mass spectrum and the eigenstates of the Higgs sector of the minimal 3 3 1 model are revisited in detail. There are discrepancies between our results and previous results by another author.Comment: 20 pages, latex, two figures. One note and one reference are adde