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Further Couplings
In this section we collect information on the two routines for
running
and
, and on other couplings
of standard and non-standard particles found in the PYDAT1 and
PYTCSM common blocks. Although originally begun for applications
within the traditional particle sector, this section of PYDAT1
has rapidly expanded towards the non-standard aspects, and is thus more
of interest for applications to specific processes. It could therefore
equally well have been put somewhere else in this manual. Several other
couplings indeed appear in the PARP array in the PYPARS
common block, see section
, and the choice between
the two has largely been dictated by availability of space. The
improved simulation of the TechniColor Strawman Model, described
in [Lan02,Lan02a], and the resulting proliferation of model
parameters, has led to the introduction of the new PYTCSM
common block.
- Purpose:
- to calculate the running electromagnetic coupling
constant
. Expressions used are described in
ref. [Kle89]. See MSTU(101), PARU(101),
PARU(103) and PARU(104).
- Q2 :
- the momentum transfer scale
at which to evaluate
.
- Purpose:
- to calculate the running strong coupling constant
, e.g. in matrix elements and resonance decay widths.
(The function is not used in parton showers, however, where
formulae rather are written in terms of the relevant
values.) The first- and second-order expressions are given by
eqs. (
) and (
). See
MSTU(111) - MSTU(118) and PARU(111) - PARU(118) for options.
- Q2 :
- the momentum transfer scale
at which to evaluate
.
- Purpose:
- to give running masses of
,
,
,
,
and
quarks according to eq.
. For all other
particles, the PYMASS function is called by PYMRUN to give
the normal mass. Such running masses appear e.g. in couplings of
fermions to Higgs and technipion states.
- KF :
- flavour code.
- Q2 :
- the momentum transfer scale
at which to evaluate
.
- Note:
- The nominal values, valid at a reference scale
,
are stored in PARF(91)-PARF(96).
- Purpose:
- to give access to a number of status codes and
parameters which regulate the performance of the program as a whole.
Here only those related to couplings are described; the main
description is found in section
.
- MSTU(101) :
- (D=1) procedure for
evaluation in the PYALEM function.
- = 0 :
-
is taken fixed at the value
PARU(101).
- = 1 :
-
is running with the
scale,
taking into account corrections from fermion loops (
,
,
,
,
,
,
,
).
- = 2 :
-
is fixed, but with separate values at low
and high
. For
below (above) PARU(104) the value
PARU(101) (PARU(103)) is used. The former value is
then intended for real photon emission, the latter for
electroweak physics, e.g. of the
gauge bosons.
- MSTU(111) :
- (I, D=1) order of
evaluation in the
PYALPS function. Is overwritten in PYEEVT, PYONIA or
PYINIT calls with the value desired for the process under study.
- = 0 :
-
is fixed at the value PARU(111).
As extra safety,
PARU(117) is set in PYALPS so
that the first-order running
agrees with the desired fixed
for the
value used.
- = 1 :
- first-order running
is used.
- = 2 :
- second-order running
is used.
- MSTU(112) :
- (D=5) the nominal number of flavours assumed in
the
expression, with respect to which
is defined.
- MSTU(113) :
- (D=3) minimum number of flavours that may be
assumed in
expression, see MSTU(112).
- MSTU(114) :
- (D=5) maximum number of flavours that may be
assumed in
expression, see MSTU(112).
- MSTU(115) :
- (D=0) treatment of
singularity for
in PYALPS calls. (Relevant e.g. for QCD
matrix elements in the
limit, but not for showers, where
PYALPS is not called.)
- = 0 :
- allow it to diverge like
.
- = 1 :
- soften the divergence to
.
- = 2 :
- freeze
evolution below PARU(114), i.e.
the effective argument is
PARU(114)
.
- MSTU(118) :
- (I) number of flavours
found and used in
latest PYALPS call.
- PARU(101) :
- (D=0.00729735=1/137.04)
, the electromagnetic fine structure constant at
vanishing momentum transfer.
- PARU(102) :
- (D=0.232)
, the weak mixing angle of the
standard electroweak model.
- PARU(103) :
- (D=0.007764=1/128.8) typical
in
electroweak processes; used for
PARU(104) in the
option MSTU(101)=2 of PYALEM. Although it can technically
be used also at rather small
, this
value is mainly
intended for high
, primarily
and
physics.
- PARU(104) :
- (D=1 GeV
) dividing line between `low' and
`high'
values in the option MSTU(101)=2 of PYALEM.
- PARU(105) :
- (D=1.16639E-5 GeV
)
, the Fermi
constant of weak interactions.
- PARU(108) :
- (I) the
value obtained in the
latest call to the PYALEM function.
- PARU(111) :
- (D=0.20) fix
value assumed in
PYALPS when MSTU(111)=0 (and also in parton showers
when
is assumed fix there).
- PARU(112) :
- (I, D=0.25 GeV)
used in running
expression in PYALPS. Like MSTU(111), this value is
overwritten by the calling physics routines, and is therefore purely
nominal.
- PARU(113) :
- (D=1.) the flavour thresholds, for the effective
number of flavours
to use in the
expression, are
assumed to sit at
PARU(113)
, where
is the quark mass. May be overwritten from the calling
physics routine.
- PARU(114) :
- (D=4 GeV
)
value below which the
value is assumed constant for MSTU(115)=2.
- PARU(115) :
- (D=10.) maximum
value that PYALPS
will ever return; is used as a last resort to avoid singularities.
- PARU(117) :
- (I)
value (associated with
MSTU(118) effective flavours) obtained in latest PYALPS
call.
- PARU(118) :
- (I)
value obtained in latest
PYALPS call.
- PARU(121) - PARU(130) :
- couplings of a new
; for
fermion default values are given by the Standard Model
values,
assuming
. Since a generation dependence is now
allowed for the
couplings to fermions, the variables
PARU(121) - PARU(128) only refer to the first generation,
with the second generation in PARJ(180) - PARJ(187) and
the third in PARJ(188) - PARJ(195) following exactly the
same pattern. Note that e.g. the
width contains
squared couplings, and thus depends quadratically on the values below.
- PARU(121), PARU(122) :
- (D=-0.693,-1.) vector and axial
couplings of down type quarks to
.
- PARU(123), PARU(124) :
- (D=0.387,1.) vector and axial
couplings of up type quarks to
.
- PARU(125), PARU(126) :
- (D=-0.08,-1.) vector and axial
couplings of leptons to
.
- PARU(127), PARU(128) :
- (D=1.,1.) vector and axial
couplings of neutrinos to
.
- PARU(129) :
- (D=1.) the coupling
is
taken to be PARU(129)
(the Standard Model
coupling)
.
This gives a
partial width that
increases proportionately to the
mass.
- PARU(130) :
- (D=0.) in the decay chain
fermions, the angular distribution in
the
decays is supposed to be a mixture, with fraction
1-PARU(130) corresponding to the same angular distribution
between the four final fermions as in
(mixture
of transverse and longitudinal
's), and fraction PARU(130)
corresponding to
the same way (longitudinal
's).
- PARU(131) - PARU(136) :
- couplings of a new
;
for fermions default values are given by the Standard Model
values (i.e.
). Note that e.g. the
width contains squared couplings, and
thus depends quadratically on the values below.
- PARU(131), PARU(132) :
- (D=1.,-1.) vector and axial couplings
of a quark-antiquark pair to
; is further multiplied by the
ordinary CKM factors.
- PARU(133), PARU(134) :
- (D=1.,-1.) vector and axial couplings
of a lepton-neutrino pair to
.
- PARU(135) :
- (D=1.) the coupling
is taken to be PARU(135)
(the Standard Model
coupling)
.
This gives a
partial width that
increases proportionately to the
mass.
- PARU(136) :
- (D=0.) in the decay chain
fermions,
the angular distribution in the
decays is supposed to be a
mixture, with fraction 1-PARU(136) corresponding to the same
angular distribution between the four final fermions as in
(mixture of transverse and longitudinal
's), and fraction PARU(136) corresponding to
the same way (longitudinal
's).
- PARU(141) :
- (D=5.)
parameter of a two Higgs
doublet scenario, i.e. the ratio of vacuum expectation values.
This affects mass relations and couplings in the Higgs sector.
If the Supersymmetry simulation is switched on, IMSS(1)
nonvanishing, PARU(141) will be overwritten by RMSS(5)
at initialization, so it is the latter variable that should be set.
- PARU(142) :
- (D=1.) the
coupling is
taken to be PARU(142)
(the MSSM
coupling).
- PARU(143) :
- (D=1.) the
coupling is
taken to be PARU(143)
(the MSSM
coupling).
- PARU(145) :
- (D=1.) quadratically multiplicative factor in the
partial width in left-right-symmetric models,
expected to be unity (see [Coc91]).
- PARU(146) :
- (D=1.)
parameter, enters
quadratically as multiplicative factor in the
partial width in
left-right-symmetric models (see [Coc91]).
- PARU(151) :
- (D=1.) multiplicative factor in the
squared Yukawa coupling, and thereby in the
partial width and the
and other
cross sections. Specifically,
PARU(151)
, i.e. it
corresponds to the
factor of [Hew88].
- PARU(161) - PARU(168) :
- (D=5*1.,3*0.) multiplicative factors
that can be used to modify the default couplings of the
particle in PYTHIA. Note that the factors enter quadratically in the
partial widths. The default values correspond to the couplings given
in the minimal one-Higgs-doublet Standard Model, and are therefore
not realistic in a two-Higgs-doublet scenario. The default values
should be changed appropriately by you. Also the last two default
values should be changed; for these the expressions of the
minimal supersymmetric Standard Model (MSSM) are given to show
parameter normalization. Alternatively, the SUSY machinery can
generate all the couplings for IMSS(1), see MSTP(4).
- PARU(161) :
coupling to down type quarks.
- PARU(162) :
coupling to up type quarks.
- PARU(163) :
coupling to leptons.
- PARU(164) :
coupling to
.
- PARU(165) :
coupling to
.
- PARU(168) :
coupling to
in
loops, in MSSM
.
- PARU(171) - PARU(178) :
- (D=7*1.,0.) multiplicative factors
that can be used to modify the default couplings of the
particle in PYTHIA. Note that the factors enter quadratically in
partial widths. The default values for PARU(171) - PARU(175)
correspond to the couplings given to
in the minimal
one-Higgs-doublet Standard Model, and are therefore not realistic
in a two-Higgs-doublet scenario. The default values should
be changed appropriately by you. Also the last two default
values should be changed; for these the expressions of the
minimal supersymmetric Standard Model (MSSM) are given to show
parameter normalization. Alternatively, the SUSY machinery can generate
all the couplings for IMSS(1), see MSTP(4).
- PARU(171) :
coupling to down type quarks.
- PARU(172) :
coupling to up type quarks.
- PARU(173) :
coupling to leptons.
- PARU(174) :
coupling to
.
- PARU(175) :
coupling to
.
- PARU(176) :
coupling to
, in MSSM
.
- PARU(177) :
coupling to
, in MSSM
.
- PARU(178) :
coupling to
in
loops, in MSSM
.
- PARU(181) - PARU(190) :
- (D=3*1.,2*0.,2*1.,3*0.)
multiplicative factors that can be used to modify the default
couplings of the
particle in PYTHIA. Note that the factors
enter quadratically in partial widths. The default values for
PARU(181) - PARU(183) correspond
to the couplings given to
in the minimal one-Higgs-doublet
Standard Model, and are therefore not realistic in a
two-Higgs-doublet scenario. The default values should
be changed appropriately by you. PARU(184) and PARU(185)
should be vanishing at the tree level, in the absence of CP
violating phases in the Higgs sector, and are so set;
normalization of these couplings agrees with what is used for
and
. Also the other default values should be changed; for
these the expressions of the Minimal Supersymmetric Standard
Model (MSSM) are given to show parameter normalization. Alternatively,
the SUSY machinery can generate all the couplings for IMSS(1),
see MSTP(4).
- PARU(181) :
coupling to down type quarks.
- PARU(182) :
coupling to up type quarks.
- PARU(183) :
coupling to leptons.
- PARU(184) :
coupling to
.
- PARU(185) :
coupling to
.
- PARU(186) :
coupling to
(or
to
), in MSSM
.
- PARU(187) :
coupling to
(or
to
), in MSSM
.
- PARU(188) :
- As PARU(186), but coupling to
rather than
.
- PARU(189) :
- As PARU(187), but coupling to
rather than
.
- PARU(190) :
coupling to
in
loops, 0 in MSSM.
- PARU(191) - PARU(195) :
- (D=4*0.,1.) multiplicative factors
that can be used to modify the couplings of the
particle
in PYTHIA. Currently only PARU(195) is in use. See above for
related comments.
- PARU(195) :
coupling to
(or
to
), in MSSM
.
- PARU(197):
- (D=0.)
coupling to
within a two-Higgs-doublet model.
- PARU(198):
- (D=0.)
coupling to
within a two-Higgs-doublet model.
- PARJ(180) - PARJ(187) :
- couplings of the
second generation fermions to the
, following the same pattern
and with the same default values as the first one in
PARU(121) - PARU(128).
- PARJ(188) - PARJ(195) :
- couplings of the
third generation fermions to the
, following the same pattern
and with the same default values as the first one in
PARU(121) - PARU(128).
- Purpose:
- to give access to a number of switches and parameters
which regulate the simulation of the TechniColor Strawman Model
[Lan02,Lan02a], plus a few further parameters related to
the simulation of compositeness, mainly in earlier incarnations of
TechniColor.
- ITCM(1) :
- (D=4)
, number of technicolors;
fixes the relative values of
and
.
- ITCM(2) :
- (D=0) Topcolor model.
- = 0 :
- Standard Topcolor. Third generation quark couplings to
the coloron are proportional to
, see RTCM(21)
below; first two generations are proportional to
.
- = 1 :
- Flavor Universal Topcolor. All quarks couple with
strength proportional to
.
- ITCM(5) :
- (D=0) presence of anomalous couplings in standard model
processes, see subsection
for further details.
- = 0 :
- absent.
- = 1 :
- left-left isoscalar model, with only
and
quarks composite (at the probed scale).
- = 2 :
- left-left isoscalar model, with all quarks composite.
- = 3 :
- helicity-non-conserving model, with only
and
quarks composite (at the probed scale).
- = 4 :
- helicity-non-conserving model, with all quarks composite.
- = 5 :
- coloured technihadrons, affecting the standard QCD
cross sections by the exchange of Coloron or Colored Technirho,
see subsection
.
- RTCM(1) :
- (D=82 GeV)
, the Technicolor decay
constant.
- RTCM(2) :
- (D=4/3)
, charge of up-type technifermion;
the down-type technifermion has a charge
.
- RTCM(3) :
- (D=1/3)
, where
is the
mixing angle between isotriplet technipion interaction and mass
eigenstates.
- RTCM(4) :
- (D=
)
, where
is the
mixing angle between the isosinglet
interaction
and mass eigenstates.
- RTCM(5) :
- (D=1) Clebsch for technipi decays to charm. Appears
squared in decay rates.
- RTCM(6) :
- (D=1) Clebsch for technipi decays to bottom. Appears
squared in decay rates.
- RTCM(7) :
- (D=0.0182) Clebsch for technipi decays to top,
estimated to be
. Appears squared in decay rates.
- RTCM(8) :
- (D=1) Clebsch for technipi decays to
.
Appears squared in decay rates.
- RTCM(9) :
- (D=0) squared Clebsch for isotriplet technipi decays
to gluons.
- RTCM(10) :
- (D=4/3) squared Clebsch for isosinglet technipi
decays to gluons.
- RTCM(11) :
- (D=0.05) technirho-techniomega mixing parameters.
Allows for isospin violating decays of the techniomega.
- RTCM(12) :
- (D=200 GeV) vector technimeson decay parameter.
Affects the decay rates of vector technimesons into technipi plus
transverse gauge boson.
- RTCM(13) :
- (D=200 GeV) axial mass parameter for
technivector decays to transverse gauge bosons and technipions.
- RTCM(21) :
- (D=
) tangent of Topcolor mixing angle,
in the scenario with coloured technihadrons described in subsection
and switched on with ITCM(5)=5.
For ITCM(2)=0, the coupling of the
to light
quarks is suppressed by RTCM(21)
whereas the coupling to
heavy (
and
) quarks is enhanced by 1/RTCM(21)
.
For ITCM(21)=1, the coupling to quarks
is universal, and given by 1/RTCM(21)
.
- RTCM(22) :
- (D=
) sine of isosinglet technipi mixing
with Topcolor currents.
- RTCM(23) :
- (D=0) squared Clebsch for color-octet technipi decays
to charm.
- RTCM(24) :
- (D=0) squared Clebsch for color-octet technipi decays
to bottom.
- RTCM(25) :
- (D=0) squared Clebsch for color-octet technipi decays
to top.
- RTCM(26) :
- (D=5/3) squared Clebsch for color-octet technipi
decays to gluons.
- RTCM(27) :
- (D=250 GeV) color-octet technirho decay parameter for
decays to technipi plus gluon.
- RTCM(28) :
- (D=250 GeV) hard mixing parameter between
color-octet technirhos.
- RTCM(29) :
- (D=
) magnitude of
element of the
U(2) matrices that diagonalize U-type technifermion condensates.
- RTCM(30) :
- (D=0 Radians) phase for the element described above,
RTCM(29).
- RTCM(31) :
- (D=
) Magnitude of
element of the
U(2) matrices that diagonalize D-type technifermion condensates.
- RTCM(32) :
- (D=0 Radians) phase for the element described above,
RTCM(31).
- RTCM(33) :
- (D=1) if
, then
is redefined to be
.
It thus prevents the coloron from becoming wider than its mass.
- RTCM(41) :
- compositeness scale
, used in processes
involving excited fermions, and for standard model processes when
ITCM(5) is between 1 and 4.
- RTCM(42) :
- (D=1.) sign of the interference term between the
standard cross section and the compositeness term (
parameter);
should be
; used for standard model processes when ITCM(5)
is between 1 and 4.
- RTCM(43) - RTCM(45) :
- (D=3*1.) strength of the SU(2),
U(1) and SU(3) couplings, respectively, in an excited fermion
scenario; cf.
,
and
of [Bau90].
- RTCM(46) :
- (D=0.) anomalous magnetic moment of the
in process 20;
, where
(
)
is the Standard Model value.
Next: Supersymmetry Common Blocks and
Up: The Process Generation Program
Previous: The General Switches and
  Contents
Stephen Mrenna
2005-07-11