Left-Right-Symmetry Processes
At current energies, the world is left-handed, i.e. the Standard Model
contains an SU(2)_L group. Left-right symmetry at some larger
scale implies the need for an SU(2)_R group. Thus the particle
content is expanded by right-handed Z_R^0 and W_R^+-
and right-handed neutrinos. The Higgs fields have to be in a triplet
representation, leading to doubly-charged Higgs particles, one set for
each of the two SU(2) groups. Also the number of neutral and
singly-charged Higgs states is increased relative to the Standard Model,
but a search for the lowest-lying states of this kind is no different
from e.g. the freedom already accorded by the MSSM Higgs scenarios.
PYTHIA implements the scenario of [Hui97].
The W_R^+- has been implemented as a simple copy of the
ordinary W^+-, with the exception that it couples to
right-handed neutrinos instead of the ordinary left-handed ones.
Thus the standard CKM matrix is used in the quark sector, and the
same vector and axial coupling strengths, leaving only the mass as
free parameter. The Z_R^0 implementation (without interference
with the photon or the ordinary Z^0) allows decays both to
left- and right-handed neutrinos, as well as other fermions, according
to one specific model ansatz. Obviously both the W_R^+-
and the Z_R^0 descriptions are likely to be simplifications,
but provide a starting point.
For the doubly-charged Higgs bosons, the main decay modes implemented are
H_L^++ → W_L^+ W_L^+, l_i^+ l_j^+ (i, j generation
indices) and H_R^++ → W_R^+ W_R^+, l_i^+ l_j^+.
The right-handed neutrinos can be allowed to decay further. Assuming them
to have a mass below that of W_R^+-, they decay to three-body
states via a virtual W_R^+-, nu_Rl → l+- f fbar',
where both lepton charges are allowed owing to the Majorana character
of the neutrinos. If there is a significant mass splitting, also
sequential decays nu_Rl → l+- l'-+ nu'_Rl are allowed.
Currently the decays are isotropic in phase space. If the neutrino
masses are close to or above the W_R^ ones, this description
has to be substituted by a sequential decay via a real W_R^
(not implemented, but actually simpler to do than the one here).
Production processes
A few different production processes have been implemented, which normally
would not overlap and therefore could be run together.
flag LeftRightSymmmetry:all
(default = off)
Common switch for the group of implemented processes within a
left-right-symmetric scenario.
flag LeftRightSymmmetry:ffbar2ZR
(default = off)
Scatterings f fbar → Z_R^0.
Code 3101.
flag LeftRightSymmmetry:ffbar2WR
(default = off)
Scatterings f fbar' → W_R^+.
Code 3102.
flag LeftRightSymmmetry:ll2HL
(default = off)
Scatterings l_i l_j → H_L^--.
Code 3121.
flag LeftRightSymmmetry:lgm2HLe
(default = off)
Scatterings l_i gamma → H_L^-- e^+.
Code 3122.
flag LeftRightSymmmetry:lgm2HLmu
(default = off)
Scatterings l_i gamma → H_L^-- mu^+.
Code 3123.
flag LeftRightSymmmetry:lgm2HLtau
(default = off)
Scatterings l_i gamma → H_L^-- tau^+.
Code 3124.
flag LeftRightSymmmetry:ff2HLff
(default = off)
Scatterings f_1 f_2 → H_L^-- f_3 f_4 via WW fusion.
Code 3125.
flag LeftRightSymmmetry:ffbar2HLHL
(default = off)
Scatterings f fbar → H_L^++ H_L^--.
Code 3126.
flag LeftRightSymmmetry:ll2HR
(default = off)
Scatterings l_i l_j → H_R^--.
Code 3141.
flag LeftRightSymmmetry:lgm2HRe
(default = off)
Scatterings l_i gamma → H_R^-- e^+.
Code 3142.
flag LeftRightSymmmetry:lgm2HRmu
(default = off)
Scatterings l_i gamma → H_R^-- mu^+.
Code 3143.
flag LeftRightSymmmetry:lgm2HRtau
(default = off)
Scatterings l_i gamma → H_R^-- tau^+.
Code 3144.
flag LeftRightSymmmetry:ff2HRff
(default = off)
Scatterings f_1 f_2 → H_R^-- f_3 f_4 via WW fusion.
Code 3145.
flag LeftRightSymmmetry:ffbar2HRHR
(default = off)
Scatterings f fbar → H_R^++ H_R^--.
Code 3146.
Parameters
The basic couplings of the model are
parm LeftRightSymmmetry:gL
(default = 0.64; minimum = 0.0)
lefthanded coupling g_L = e / sin(theta).
parm LeftRightSymmmetry:gR
(default = 0.64; minimum = 0.0)
righthanded coupling g_R, assumed the same as g_L.
parm LeftRightSymmmetry:vL
(default = 5.; minimum = 0.0)
vacuum expectation value v_L (in GeV) for the left-triplet.
The corresponding vacuum expectation value v_R is assumed
given by v_R = sqrt(2) M_WR / g_R and is not stored explicitly.
The Yukawa couplings of a lepton pair to a H^--, assumed the
same for H_L^-- and H_R^--, is described by a symmetric
3-by-3 matrix. The default matrix is dominated by the diagonal elements
and especially by the tau tau one.
parm LeftRightSymmmetry:coupHee
(default = 0.1; minimum = 0.0)
Yukawa coupling for H^-- → e- e-.
parm LeftRightSymmmetry:coupHmue
(default = 0.01; minimum = 0.0)
Yukawa coupling for H^-- → mu- e-.
parm LeftRightSymmmetry:coupHmumu
(default = 0.1; minimum = 0.0)
Yukawa coupling for H^-- → mu- mu-.
parm LeftRightSymmmetry:coupHtaue
(default = 0.01; minimum = 0.0)
Yukawa coupling for H^-- → tau- e-.
parm LeftRightSymmmetry:coupHtaumu
(default = 0.01; minimum = 0.0)
Yukawa coupling for H^-- → tau- mu-.
parm LeftRightSymmmetry:coupHtautau
(default = 0.3; minimum = 0.0)
Yukawa coupling for H^-- → tau- tau-.