The default antenna functions used in VINCIA largely resemble those used by Gehrmann, de-Ridder, and Glover (GGG, see below), but also, e.g., the ones used by ARIADNE and a few more are provided as alternatives. Yet others can be defined by the user.
To use an alternative set of antennae (i.e., non-default), for instance to estimate uncertainties, a convenient way of specifying a collection of non-default parameters is to use
word
VinciaShower:antennaFile
(default = none
)antennae/
(see below).
More user-defined antennae can be added and stored in the same
directory, if desired. To use them with a program that
runs in your main VINCIA directory (default), include the following
command in your main program or command file:
VinciaShower:antennaFile = antennae/antennae-GGG.cmnd
(Here we used the "GGG" antennae for illustration.)
To use a user-defined antenna set with a program that does not run in your
VINCIA main directory, or if the antennae you want to use are not stored
in the antennae/
directory, give the full path- and filename instead, as in
Vincia:antennaFile = /Users/skands/vincia/antennae/antennae-GGG.cmnd
Note that the format of the antenna files is the same as that of ordinary PYTHIA 8 command files, hence any combination of VINCIA and PYTHIA 8 commands could in principle be included to define an antenna set, but in general we advise to keep only specific antenna-related parameters in the antenna definition files, to avoid confusions/conflicts between your main command file(s) and the antenna file.
The default antennae have been chosen to be close to the GGG ones
and have been verified to give a good average agreement with Z→n
matrix elements. The following two examples, included with the
VINCIA package in the antennae/
subdirectory, have been defined so as to try to span a
reasonable min-max uncertainty range:
Mass corrections are implemented systematically in VINCIA. The following switches control which quarks and leptons are treated as massive during the event evolution.
flag
VinciaShower:isMassiveS
(default = false
)flag
VinciaShower:isMassiveC
(default = true
)flag
VinciaShower:isMassiveB
(default = true
)flag
VinciaShower:isMassiveTau
(default = true
)Note: new-physics particles will generally be treated as massive if their masses are larger than the lightest quark for which mass corrections are switched on.
The number of quark flavours allowed in gluon splittings, phase space permitting, is given by
mode
VinciaShower:nGluonToQuark
(default = 5
; minimum = 0
; maximum = 5
)The 2→3 (LL) VINCIA antennae have names such as
Vincia:qQ:emit
(for gluon emission off a qqbar
antenna), Vincia:qg:split
(for gluon splitting to a
quark-antiquark pair inside a qg antenna).Vincia:AB:x
, where A
and B
are
the "mothers" and x
is either emit
or
split
, depending on whether the process is gluon emission
or gluon splitting.
The radiating (parent) antenna is interpreted as
spanned between the Les Houches colour tag of
A
and the anti-colour tag of B
, see
illustration to the right.
The functional form of the antennae are specified by giving the
coefficients of a double Laurent series in the two branching
invariants (the third invariant, specifying a
rotation around the dipole axis, is chosen uniformly).
The Laurent expansion starts at power (-1,-1)
corresponding to the double singularity.
For so-called "global" antennae (the default in VINCIA),
each antenna is fully specified by giving the
coefficients LaurentC(i,j)
of the following expansion:
A(y_ar,y_rb;s_AB) = 1/s_AB 4 pi
alpha_s chargeFactor LaurentC(i,j) pow(y_ar,i) pow(y_rb,j);
where i
and
j
are implicitly summed over,
s_AB
is the mass of the mother antenna,
chargeFactor
should be normalized to tend to NC
raised to the number of new color lines created in
the splitting in
the large-NC limit (i.e., the limiting value should be 3 for gluon
emission and 1 for gluon splitting), and y_ar,y_rb
are the
branching invariants scaled by the mass of the mother antenna,
y_ij = s_ij/s_AB
.
The coefficients with negative i
or j
indices are universal and should not be
changed by the user. Strictly for theoretical testing purposes, we
provide a possibility to switch off all but the Eikonal terms (i.e.,
removing the additional collinear-singular terms from the antenna
functions), using the following switch
flag
VinciaShower:useCollinearTerms
(default = on
)on
for normal runs. Setting it to off
will
set all collinear-singular non-Eikonal term coefficients to zero.
Finite terms, i.e., with both indices greater than or equal to zero, are arbitrary and in general the best choice to make will depend on the specific process considered. They are therefore not to be regarded as "tunable" parameters, but rather as an independent way of estimating the uncertainty due do uncalculated higher orders, an uncertainty which can be explicitly reduced by matrix-element matching. The default is therefore to allow these terms to be nonzero, but for special applications it may be convenient to have one global switch that switches them on and off:
flag
VinciaShower:useFiniteTerms
(default = on
)on
for normal runs. Setting it to off
will
set all finite term coefficients to zero.
parm
Vincia:CollinearGluonSplitting
(default = 0.0
; minimum = 0.0
; maximum = 1
)flag
Vincia:qQ:emit
(default = on
)parm
Vincia:qQ:emit:chargeFactor
(default = 2.66666667
)parm
Vincia:qQ:emit:LaurentC(-1,-1)
(default = 2.0
)parm
Vincia:qQ:emit:LaurentC(-1,0)
(default = -2.0
)parm
Vincia:qQ:emit:LaurentC(0,-1)
(default = -2.0
)parm
Vincia:qQ:emit:LaurentC(-1,1)
(default = 1.0
)parm
Vincia:qQ:emit:LaurentC(1,-1)
(default = 1.0
)parm
Vincia:qQ:emit:LaurentC(0,0)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentC(1,0)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentC(0,1)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentC(2,0)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentC(0,2)
(default = 0.0
)flag
Vincia:qg:emit
(default = on
)parm
Vincia:qg:emit:chargeFactor
(default = 3.0
)parm
Vincia:qg:emit:LaurentC(-1,-1)
(default = 2.0
)parm
Vincia:qg:emit:LaurentC(-1,0)
(default = -2.0
)parm
Vincia:qg:emit:LaurentC(0,-1)
(default = -2.0
)parm
Vincia:qg:emit:LaurentC(1,-1)
(default = 1.0
)parm
Vincia:qg:emit:LaurentC(-1,1)
(default = 1.0
)parm
Vincia:qg:emit:LaurentC(2,-1)
(default = -1.0
)parm
Vincia:qg:emit:LaurentC(0,0)
(default = 2.0
)parm
Vincia:qg:emit:LaurentC(1,0)
(default = 0.0
)parm
Vincia:qg:emit:LaurentC(0,1)
(default = 0.0
)flag
Vincia:gg:emit
(default = on
)parm
Vincia:gg:emit:chargeFactor
(default = 3.0
)parm
Vincia:gg:emit:LaurentC(-1,-1)
(default = 2.0
)parm
Vincia:gg:emit:LaurentC(-1,0)
(default = -2.0
)parm
Vincia:gg:emit:LaurentC(0,-1)
(default = -2.0
)parm
Vincia:gg:emit:LaurentC(-1,1)
(default = 1.0
)parm
Vincia:gg:emit:LaurentC(1,-1)
(default = 1.0
)parm
Vincia:gg:emit:LaurentC(2,-1)
(default = -1.0
)parm
Vincia:gg:emit:LaurentC(-1,2)
(default = -1.0
)parm
Vincia:gg:emit:LaurentC(0,0)
(default = 2.0
)parm
Vincia:gg:emit:LaurentC(1,0)
(default = 0.0
)parm
Vincia:gg:emit:LaurentC(0,1)
(default = 0.0
)flag
Vincia:qg:split
(default = on
)parm
Vincia:qg:split:chargeFactor
(default = 1.0
)parm
Vincia:qg:split:LaurentC(-1,-1)
(default = 0.0
)parm
Vincia:qg:split:LaurentC(-1,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentC(-1,1)
(default = 0.0
)parm
Vincia:qg:split:LaurentC(0,-1)
(default = 0.5
)parm
Vincia:qg:split:LaurentC(1,-1)
(default = -1.0
)parm
Vincia:qg:split:LaurentC(2,-1)
(default = 1.0
)parm
Vincia:qg:split:LaurentC(0,0)
(default = 0.3
)parm
Vincia:qg:split:LaurentC(1,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentC(0,1)
(default = 0.0
)flag
Vincia:gg:split
(default = on
)parm
Vincia:gg:split:chargeFactor
(default = 1.0
)parm
Vincia:gg:split:LaurentC(-1,-1)
(default = 0.0
)parm
Vincia:gg:split:LaurentC(-1,0)
(default = 0.0
)parm
Vincia:gg:split:LaurentC(-1,1)
(default = 0.0
)parm
Vincia:gg:split:LaurentC(0,-1)
(default = 0.5
)parm
Vincia:gg:split:LaurentC(1,-1)
(default = -1.0
)parm
Vincia:gg:split:LaurentC(2,-1)
(default = 1.0
)parm
Vincia:gg:split:LaurentC(0,0)
(default = 0.3
)parm
Vincia:gg:split:LaurentC(1,0)
(default = 0.0
)parm
Vincia:gg:split:LaurentC(0,1)
(default = 0.0
)flag
Vincia:qq:emit:useMassTerms
(default = on
)parm
Vincia:qQ:emit:DenominatorMassPrefactor
(default = 0.0
)parm
Vincia:qQ:emit:LaurentM(1,0,0,0)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentM(1,0,1,0)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentM(2,0,0,0)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentM(2,0,1,0)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentM(1,1,0,0)
(default = 0.0
)parm
Vincia:qQ:emit:LaurentM(1,1,1,0)
(default = 0.0
)flag
Vincia:qg:emit:useMassTerms
(default = on
)parm
Vincia:qg:emit:LaurentM(1,0,0)
(default = 0.0
)parm
Vincia:qg:emit:LaurentM(1,1,0)
(default = 0.0
)parm
Vincia:qg:emit:LaurentM(1,0,1)
(default = 0.0
)parm
Vincia:qg:emit:LaurentM(2,0,0)
(default = 0.0
)parm
Vincia:qg:emit:LaurentM(2,1,0)
(default = 0.0
)parm
Vincia:qg:emit:LaurentM(2,0,1)
(default = 0.0
)parm
Vincia:qg:emit:LaurentM(2,-1,0)
(default = 0.0
)parm
Vincia:qg:emit:LaurentM(2,-1,1)
(default = 0.0
)parm
Vincia:qg:emit:LaurentMtilde(2,-1,-1,2)
(default = 0.0
)parm
Vincia:qg:emit:LaurentMtilde(3,-1,-1,1)
(default = 0.0
)parm
Vincia:qg:emit:LaurentMtilde(4,-1,-1,1)
(default = 0.0
)flag
Vincia:gg:emit:useMassTerms
(default = on
)flag
Vincia:qg:split:useMassTerms
(default = on
)parm
Vincia:qg:split:LaurentM(1,0,0,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentM(1,0,1,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentM(1,0,0,1)
(default = 0.0
)parm
Vincia:qg:split:LaurentM(2,0,0,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentM(2,0,0,1)
(default = 0.0
)parm
Vincia:qg:split:LaurentM(2,0,1,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(0,2,0,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(0,2,0,1)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(0,2,1,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(1,0,0,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(1,0,0,1)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(1,0,1,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(2,0,0,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(2,0,0,1)
(default = 0.0
)parm
Vincia:qg:split:LaurentMtilde(2,0,1,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentCtilde(0,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentCtilde(0,1)
(default = 0.0
)parm
Vincia:qg:split:LaurentCtilde(0,2)
(default = 0.0
)parm
Vincia:qg:split:LaurentCtilde(1,0)
(default = 0.0
)parm
Vincia:qg:split:LaurentCtilde(1,1)
(default = 0.0
)parm
Vincia:qg:split:LaurentCtilde(2,0)
(default = 0.0
)flag
Vincia:gg:split:useMassTerms
(default = on
)parm
Vincia:gg:split:LaurentM(2,0,0)
(default = 0.0
)parm
Vincia:gg:split:LaurentM(2,0,1)
(default = 0.0
)parm
Vincia:gg:split:LaurentM(2,1,0)
(default = 0.0
)parm
Vincia:gg:split:LaurentCtilde(0,0)
(default = 0.0
)parm
Vincia:gg:split:LaurentCtilde(0,1)
(default = 0.0
)parm
Vincia:gg:split:LaurentCtilde(0,2)
(default = 0.0
)parm
Vincia:gg:split:LaurentCtilde(1,0)
(default = 0.0
)parm
Vincia:gg:split:LaurentCtilde(1,1)
(default = 0.0
)parm
Vincia:gg:split:LaurentCtilde(2,0)
(default = 0.0
)