Higgs Mechanism with Type-II Nambu-Goldstone Bosons at Finite Chemical Potential

When the spontaneous symmetry breaking occurs for systems without Lorentz covariance, there arises possible mismatch, $N_{\rm NG} < N_{\rm BG}$, between numbers of Nambu-Goldstone (NG) bosons ($N_{\rm NG}$) and the numbers of broken generators ($N_{\rm BG}$. In such a situation, so-called type-II NG bosons emerge. We study how the gauge bosons acquire masses through the Higgs mechanism under this mismatch by employing gauge theories with complex scalar field at finite chemical potential and by enforcing "charge" neutrality. To separate the physical spectra from unphysical ones, the $R_{\xi}$ gauge is adopted. Not only massless NG bosons but also massive scalar bosons generated by the chemical potential are absorbed into spatial components of the gauge bosons. Although the chemical potential induces a non-trivial mixings among the scalar bosons and temporal components of the gauge bosons, it does not affect the structure of the physical spectra, so that the total number of physical modes is not modified even for $N_{\rm NG} < N_{\rm BG}$.Comment: 7 pages, 2 figure

Search for non-SM Higgses at LEP

The four LEP experiments, ALEPH, DELPHI, L3 and OPAL, have searched for Higgs bosons predicted by a large number of extensions of the Standard Model. Flavor independent searches are presented for the h$^{0}$Z$^{0}$ process in which the h$^{0}$ decays hadronically. Search results are also presented for fermiophobic Higgs bosons, invisibly decaying Higgs bosons, charged Higgs bosons and the neutral Higgs bosons in the MSSM.Comment: 4 pages, 4 figures, to be published in the Proceedings of XXXVI Rencontres de Moriond: QCD, March 200

Remarks on nonrelativistic Goldstone bosons

We discuss excitations in nonrelativistic field theories with spontaneous breaking of a continuous global symmetry. It is known that in such systems there are two types of Goldstone bosons (Type A and Type B) whose dispersion law is generically linear or quadratic, respectively. We show that Type B Goldstone bosons may have gapped partners which we call almost-Goldstone bosons. With some nondegeneracy assumption about the low-energy effective action, the total number of Goldstone and almost-Goldstone bosons adds up to the number of broken symmetry generators. We propose that deviations of the dispersion law of Goldstone bosons from linearity at small momenta may serve as a signature of small breaking of time-reversal symmetry

Low Energy Theorems in N=1 Supersymmetric Theory

In N=1 supersymmetric theories, quasi Nambu-Goldstone (QNG) bosons appear in addition to ordinary Nambu-Goldstone (NG) bosons when the global symmetry G breaks down spontaneously. We investigate two-body scattering amplitudes of these bosons in the low-energy effective Lagrangian formalism. They are expressed by the curvature of Kahler manifold. The scattering amplitudes of QNG bosons are shown to coincide with those of NG bosons though the effective Lagrangian contains an arbitrary function, and those with odd number of QNG bosons all vanish.Comment: LaTeX, 18 pages, 3 figures, typos corrected, references adde

Bound states of three and four resonantly interacting particles

We present an exact diagrammatic approach for the problem of dimer-dimer scattering in 3D for dimers being a resonant bound state of two fermions in a spin-singlet state, with corresponding scattering length $a_F$. Applying this approach to the calculation of the dimer-dimer scattering length $a_B$, we recover exactly the already known result $a_B=0.60 a_F$. We use the developed approach to obtain new results in 2D for fermions as well as for bosons. Namely, we calculate bound state energies for three $bbb$ and four $bbbb$ resonantly interacting bosons in 2D. For the case of resonant interaction between fermions and bosons we calculate exactly bound state energies of the following complexes: two bosons plus one fermion $bbf$, two bosons plus two fermions $bf_{\uparrow}bf_{\downarrow}$, and three bosons plus one fermion $bbbf$.Comment: 10 pages, 9 figure