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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.
LeftRightSymmmetry:all
On
Off
(
default =
off
)
Common switch for the group of implemented processes within a left-right-symmetric scenario.
LeftRightSymmmetry:ffbar2ZR
On
Off
(
default =
off
)
Scatterings
f fbar → Z_R^0
. Code 3101.
LeftRightSymmmetry:ffbar2WR
On
Off
(
default =
off
)
Scatterings
f fbar' → W_R^+
. Code 3102.
LeftRightSymmmetry:ll2HL
On
Off
(
default =
off
)
Scatterings
l_i l_j → H_L^--
. Code 3121.
LeftRightSymmmetry:lgm2HLe
On
Off
(
default =
off
)
Scatterings
l_i gamma → H_L^-- e^+
. Code 3122.
LeftRightSymmmetry:lgm2HLmu
On
Off
(
default =
off
)
Scatterings
l_i gamma → H_L^-- mu^+
. Code 3123.
LeftRightSymmmetry:lgm2HLtau
On
Off
(
default =
off
)
Scatterings
l_i gamma → H_L^-- tau^+
. Code 3124.
LeftRightSymmmetry:ff2HLff
On
Off
(
default =
off
)
Scatterings
f_1 f_2 → H_L^-- f_3 f_4
via
WW
fusion. Code 3125.
LeftRightSymmmetry:ffbar2HLHL
On
Off
(
default =
off
)
Scatterings
f fbar → H_L^++ H_L^--
. Code 3126.
LeftRightSymmmetry:ll2HR
On
Off
(
default =
off
)
Scatterings
l_i l_j → H_R^--
. Code 3141.
LeftRightSymmmetry:lgm2HRe
On
Off
(
default =
off
)
Scatterings
l_i gamma → H_R^-- e^+
. Code 3142.
LeftRightSymmmetry:lgm2HRmu
On
Off
(
default =
off
)
Scatterings
l_i gamma → H_R^-- mu^+
. Code 3143.
LeftRightSymmmetry:lgm2HRtau
On
Off
(
default =
off
)
Scatterings
l_i gamma → H_R^-- tau^+
. Code 3144.
LeftRightSymmmetry:ff2HRff
On
Off
(
default =
off
)
Scatterings
f_1 f_2 → H_R^-- f_3 f_4
via
WW
fusion. Code 3145.
LeftRightSymmmetry:ffbar2HRHR
On
Off
(
default =
off
)
Scatterings
f fbar → H_R^++ H_R^--
. Code 3146.
Parameters
The basic couplings of the model are
LeftRightSymmmetry:gL
(
default =
0.64
;
minimum = 0.0
)
lefthanded coupling
g_L = e / sin(theta)
.
LeftRightSymmmetry:gR
(
default =
0.64
;
minimum = 0.0
)
righthanded coupling
g_R
, assumed the same as
g_L
.
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.
LeftRightSymmmetry:coupHee
(
default =
0.1
;
minimum = 0.0
)
Yukawa coupling for
H^-- → e- e-
.
LeftRightSymmmetry:coupHmue
(
default =
0.01
;
minimum = 0.0
)
Yukawa coupling for
H^-- → mu- e-
.
LeftRightSymmmetry:coupHmumu
(
default =
0.1
;
minimum = 0.0
)
Yukawa coupling for
H^-- → mu- mu-
.
LeftRightSymmmetry:coupHtaue
(
default =
0.01
;
minimum = 0.0
)
Yukawa coupling for
H^-- → tau- e-
.
LeftRightSymmmetry:coupHtaumu
(
default =
0.01
;
minimum = 0.0
)
Yukawa coupling for
H^-- → tau- mu-
.
LeftRightSymmmetry:coupHtautau
(
default =
0.3
;
minimum = 0.0
)
Yukawa coupling for
H^-- → tau- tau-
.
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