Bound state models for fermion Regge poles

Trajectories of fermion Regge poles are calculated in a model in which a spin $\text{1}\text{2}$ particle is bound to a spin 0 core. The leading trajectory with parity $\text{(?1)}{}^{\mathrm{<mtext>j?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ is much like the boson trajectory generated by similar interactions. The opposite parity trajectory satisfies the constraints of MacDowell symmetry, yet is totally distinct for s>0. The model produces a trajectory which above the elastic threshold has a small negative Im α and an increasing Re α. Such a trajectory produces poles on the physical sheet of the energy plane.     

Properties of fermion mixings in intersecting D-brane models

We consider the Yukawa couplings for quarks and leptons in the context of Pati–Salam model using intersecting D-brane models where the Yukawa coupling matrices are rank one in a simple choice of family replication. The CKM mixings can be explained by perturbing the rank 1 matrix using higher order terms involving new Higgs fields available in the model. We show that the near bi-large neutrino mixing angles can be naturally explained, choosing the light neutrino mass matrix to be type II seesaw dominant. The predicted value of U_e3$U_{e3}$ is in the range ?0.05–0.15$?0.05\text{–}0.15$. In the quark sector, V_cb$V_{cb}$ is naturally close to the strange/bottom quark mass ratio and we obtain an approximate relation V_ubV_cb?(ms/mb)²V_us$V_{ub}{V}_{cb}?{(m_s/m_b)}^2{V}_{us}$. The geometrical interpretations of the neutrino mixings are also discussed.     

Goldstone fermion couplings and supersymmetry breaking in superstring models

We re-examine supersymmetry breaking in the observable sectors of superstring-inspired supergravity models by computing Goldstone fermion couplings at the one-loop level. We find that a single global U (1) phase invariance is sufficient to forbid masses for gauge non-singlet chiral scalar bosons, and that Heisenberg symmetry is not necessary.     

Path-integral formulation of chiral invariant fermion models in two dimensions

We study the Thirring and chiral-invariant Gross-Neveu (CGN) models using the functional integral method. By introducing an auxiliary vector field we disclose a relation with two-dimensional gauge theories coupled to fermions and then extend a technique based on a chiral change in the functional variables to study purely fermionic models.We obtain the exact Klaiber solution for the massless Thirring model (for spin $\text{1}\text{2}$) in a very simple way and we then extend our technique to investigate the CGN model. We show the factorization of a free fermionic part at the level of Green functions on very general grounds. We then impose certain restrictions on the behavior of the fields — which render our treatment exact only in the zero winding number sector, but allow the computation of the U(1) part of the CGN Green functions exactly, showing, in particular, its complete decoupling from the color part and the almost long-range order behaviour in the infrared region.In our approach, the non-triviality of the jacobian arising from the chiral transformation — directly related to the topological density and the axial anomaly — appears to be crucial for the functional integral treatment of these models.     

Complete double-projection of light fermion masses in supersymmetric composite models

We present some general classes of supersymmetric models in which the 't Hooft anomaly-matching conditions are precisely satisfied by quasi-Goldstone fermions (QGFs) and hence mass of all the light composite fermions is double-protected by supersymmetry and chiral symmetry. To find this kind of models in an economic way we show that the low-energy spectrum consistent with chiral symmetry is exhausted by QGFs whenever there exists a complementary Higgs picture of the QGF model.     

Hamiltonian models of interacting fermion fields in quantum field theory

We consider Hamiltonian models representing an arbitrary number of spin 1 / 2 fermion quantum fields interacting through arbitrary processes of creation or annihilation of particles. The fields may be massive or massless. The interaction form factors are supposed to satisfy some regularity conditions in both position and momentum space. Without any restriction on the strength of the interaction, we prove that the Hamiltonian identifies to a self-adjoint operator on a tensor product of antisymmetric Fock spaces and we establish the existence of a ground state. Our results rely on new interpolated \(N_\tau \) estimates. They apply to models arising from the Fermi theory of weak interactions, with ultraviolet and spatial cutoffs.

     

Galaxies as gravitational lenses: Realistic models

The gravitational lens effects associated with a transparent mass distribution are quite different from those of the well-known opaque sphere. We have shown that any spherical galaxy whose mass distribution, when projected onto the plane of the sky, decreases outward from the center of the galaxy and diverges less rapidly than 1/h ash0, must always produce an odd number of images, usually one or three, of a source located behind the galaxy. Using optical scalar techniques, the amplification of each image can readily be obtained. For a given source and galaxy, we can define a dimensionless focal length, a function of impact parameter, and a dimensionless distance factor, depending on lens parameters and source distance. The central value of the ratio of these quantities determines the multiplicity of the images. The mass distribution of the galaxy is a crucial function, and we show in some detail how this affects the various focal lengths.     

On fermion mass hirerachies in MSSM-like quiver models with stringy corrections

Using instanton effects, we discuss the problem of fermion mass hierarchies in an MSSM-like Type IIA orientifolded model with U(3) × Sp(1) × U(1) × U(1) gauge symmetry obtained from intersecting D6-branes. In the corresponding four-stack quiver, the different scales of the generated superpotential couplings offer a partial solution to fermion mass hierarchies. Using the known data with neutrino masses m_vt <~2 eVm_{v_\tau } \lesssim 2 eV, we give the magnitudes of the relevant scales.     

Electric dipole moments of charged leptons in the split fermion scenario in the two Higgs doublet model

We predict the charged lepton electric dipole moments in the split fermion scenario in the framework of the two Higgs doublet model. We observe that the numerical value of the muon (tau) electric dipole moment is of the order of the magnitude of 10^-22 e cm (10^-20 e cm) and there is an enhancement in the case of two extra dimensions, especially for the tau lepton electric dipole moment. Received: 15 July 2005, Published online: 6 October 2005     

Gauge coupling and fermion mass relations in low string scale brane models

We analyze the gauge coupling evolution in brane inspired models with U(3) x U(2) x U(1)^N symmetry at the string scale. We restrict our work to the case of brane configurations with two and three abelian factors (N = 2,3) and where only one Higgs doublet is coupled to down quarks and leptons and only one to the up quarks. We find that the correct hypercharge assignment of the standard model particles is reproduced for six viable models distinguished by different brane configurations. We investigate the third generation fermion mass relations and find that the correct low energy m_b/m_τ ratio can be obtained for b-τ Yukawa coupling equality at a string scale as low as M_S~10³ TeV. Received: 30 August 2005, Published online: 16 November 2005 PACS: 11.25.Wx, 11.25.Uv, 12.10.Kt     

Regularization of the fermion stress-energy tensor in isotropic models of the universe

Regularization of the stress-energy tensor of fermions created in isotropic cosmological models, equivalent to renormalization of the gravitational constant is performed. Energy density and pressure of created pairs are calculated for various stages of evolution and various expansion laws.     

Group theory approach to scattering III. Realistic models

We discuss how to construct a class of solvable S-matrices in arbitrary space dimensions starting from a dynamic group G and using the technique of Euclidean connection. We construct explicitly the S-matrices corresponding to the dynamic groups SO(2, 1), SO(2, 2), and SO(2, 3). The latter provides a realistic model for studying heavy-ion collisions.     

On the one-dimensional spin-1/2-Chain and its related fermion models

We study the linear anisotropic spin-1/2-Heisenberg model with periodic as well as antiperiodic boundary conditions. Using two assumptions about the eigenvalues of the related fermion models it is shown, how the exactly known energy spectrum of the periodic Heisenberg model is altered in the antiperiodic case. This investigation provides basis for a subsequent test of a Hartree-Fock approximation. It gives fairly good results for the groundstate energy and the energy dispersion of low-lying excitations. Hartree-Fock solutions with gapless excitations yield a qualitatively correct picture of the phase diagram of the Heisenberg model.     

Tevatron constraints on the Higgs boson mass in the fourth-generation fermion models revisited

Recent Tevatron exclusion interval of the masses of Higgs boson considerably reduces in case of the light quasistable fourth generation neutral lepton.     

A note on fermion and gauge couplings in field theory models for tachyon condensation

We study soliton solutions in supersymmetric scalar field theory with a class of potentials. We study both bosonic and fermionic zero-modes around the soliton solution. We study two possible couplings of gauge fields to these models. While the Born–Infeld like coupling has one normalizable mode (the zero mode), the other kind of coupling has no normalizable modes. We show that quantum mechanical problem which determines the spectrum of fluctuation modes of the scalar, fermion and the gauge field is identical. We also show that only the lowest lying mode, i.e., the zero mode, is normalizable and the rest of the spectrum is continuous.     

Heavy fermion materials

The heavy-fermion ground state occurs in a few select metallic compounds as a result of interactions between felectron and conduction-electron spins. A characteristically large electronic heat capacity at low temperature indicates that the effective electron mass of these materials is more than two orders of magnitude greater than that expected for a free-electron metal. This heavy-fermion ground state can become superconducting or antiferromagnetic, exhibiting very unusual properties. We will briefly discuss these materials, and the role of muon spin rotation in their study.     

Heavy fermion superconductivity

The phenomenon of Heavy Fermion Superconductivity in Kondo lattice systems is investigated via renormalized perturbation theory for the Anderson lattice model with inclusion of phonons. It is demonstrated how the conventional theory of superconductivity can be modified to take into account the coupling mediated by breathing of Rare Earth ions and the effect of strong local Coulomb correlations on these ions. The results give support to a recent theory of Razafimandimby, Fulde and Keller, which is based on an intermediate Fermi liquid picture.     

Heavy fermion superconductivity

The quest for a precise identification of the symmetry of the order parameter in heavy fermion systems has really started with the discovery of the complex superconducting phase diagram in UPt₃. About 10 years latter, despite numerous experiments and theoretical efforts, this is still not achieved, and we will quickly review the present status of knowledge and the main open question. Actually, the more forsaken issue of the nature of the pairing mechanism has been recently tackled by different groups with macroscopic or microscopic measurement, and significant progress have been obtained. We will discuss the results emerging from these recent studies which all support non-phonon-mediated mechanisms.     

Algebraic fermion bosonization

By exploiting the construction of charged field algebras as canonical extensions of CCR current algebras in 1+1 dimensions and nonregular representations of extended algebras, we provide an algebraic construction of local Fermi fields as ultrastrong limits of bosonic variables in all representations which are locally Fock with respect to the ground-state representation of the massless scalar field.