References - Bogoliubov Laboratory of Theoretical Physics - JINR

ASYMMETRIES AT THE ILC ENERGIES AND B-L GAUGE MODELS
E.C.F.S. Fortes, J.C. Montero, and V. Pleitez
Instituto de Física Teórica–Universidade Estadual Paulista
R. Dr. Bento Teobaldo Ferraz 271, Barra Funda
São Paulo - SP, 01140-070, Brazil
† E-mail: elaine@ift.unesp.br
Abstract
The use of polarized beams of electrons/positrons is one of the main characteristics
that can make the proposed ILC (International Linear Collider) to be able to
bring results for physics beyond the Standard Model and for unraveling the structure
of the underlying physics. In this work we study extra neutral gauge bosons
Z B−L (≡ Z ′ ) deriving from two extensions of the standard model with an extra gauge
U(1) B−L factor. Among several Z ′ proposed experiments, we study the capability
of e + e − colliders to give responses to the Z ′ existence using both, electron and
positron polarized beams. We emphasize e + e − → μ + μ − scattering through the
demonstration of graphs related to them. We analyzed left-right and polarization
asymmetries for the two models.
Most of the well motivated extensions of the standard model (SM) are those which
contain, at least, one extra neutral vector boson usually denoted by Z ′ . For instance,
left-right models [1], and grand unified theories based on SO(10) [2] or E6 [3]. For recent
review of extra neutral vector bosons see Ref. [4]. If Z and Z ′ denote the symmetry
eigenstates, then Z1 and Z2 are the mass eigenstates.
In particular we shall consider two extensions of the electroweak standard model in
which there is an extra U(1) local symmetry and their charges are B − L. Both models
are based on the gauge symmetry and its breakdown:
SU(2)L ⊗ U(1)ξ ⊗ U(1)B−L → SU(2)L ⊗ U(1)Y → U(1)em. (1)
In the first model ξ ≡ Y ′ , and it is chosen to obtain the hypercharge Y of the standard
model, given by Y = Y ′ + (B − L). Thus, in this case, the charge operator is given by
Q
e = I3 + 1
2 [Y ′ +(B − L)] . (2)
We shall call this model “flipped” model because the electric charge is partly in U(1) [5].
B−L
There are at least two models of this sort depending on the lepton number (L) attributed
to the right-handed neutrinos, see Ref. [5]. We consider here the model with 3 righthanded
neutrinos carrying L =1.
The other electroweak model has ξ ≡ Y and, the charge operator is as in the SM, i.e.,
given by [6],
Q
e = I3 + 1
Y. (3)
2
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