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FlexibleDecay

Creating model with decays

Whether decays are created for a given model is controled by the viariable

FSCalculateDecays = True;

in the model's FlexibleSUSY.m.in file.

By defaul this variable is initialized to False. In models distributed with FlexibleSUSY which support decays we do set it explicitly to True.

Which decays are included is controled by FSDecayParticles variable. It's possible values are Automatic or a list of scalars present in the model. By default it's set to

FSDecayParticles = Automatic;

which means CP-even and -odd neutral Higgs and charged Higgs bosons. As an example, in SARAH's THDM-II, Automatic is equivalen to setting

FSDecayParticles = {hh, Ah, Hpm};

One can also add other scalar. For example, to add squark decays in the SARAH's MSSM one would write

FSDecayParticles = {hh, Ah, Hpm, Su, Sd};

Configuration

FlexibleDecay requires FlexibleSUSY to be configured with a dedicaded loop library (currently this is COLLIER or LoopTools). See here for an instruction on how to do it.

Runtime options

SLHA input

Runtime options are set in FlexibleDecay block in the SLHA input file

Block FlexibleDecay
   0   1       # calculate decays (0 = no, 1 = yes)
   1   1e-5    # minimum BR to print
   2   4       # include higher order corrections in decays (0 = LO, 1 = NLO, 2 = NNLO, 3 = N^3LO, 4 = N^4LO )
   3   1       # use Thomson alpha(0) instead of alpha(m) in decays to γγ and γZ
   4   2       # off-shell decays into VV pair

The flags are:

  1. Turn calculation of decay on/off (default = 1).
  2. Minimal branching ratio to print (default = 1e-5).
  3. Maximal order of included higher order corrections (default = 4). Note that not all such corrections.
  4. Use α in the Thomson limit instead of a running one in decays to γγ and γZ. This should minimize higher order corrections.

Flag 4 controls treatment of Higgs decay to gauge bosons

  1. no off-shell decays
  2. on-shell decays above the VV threshold, single off-shell decays above the VV* threshold (V = W, Z), double off-shell below it
  3. double off-shell decays also between a VV* and VV thresholds

Flags 2, 3 and 4 influnce only the calculation of Higgs decays.

Finally, the loop library used by decays is controlled by flag 31 in block FlexibleSUSY. For decays the allowed vlues are 1 and 2. To compute decays one could set it for example as

31    1    # loop library (1 = COLLIER, 2 = LoopTools)

LibraryLink interface

FlexibleDecay can also be used via the LibraryLink interface (see here). The same options as in the case of SLHA input can be passed as (using CMSSM as an example)

Get["models/CMSSM/CMSSM_librarylink.m"];

(* Create a handle to a model given the input parameters.
   See Options[FSCMSSMOpenHandle] for all default options. *)
handle = FSCMSSMOpenHandle[
  fsSettings -> { precisionGoal -> 1.*^-4 },
  fsSMParameters -> { Mt -> 173.3 },
  fsModelParameters -> {
  m0 -> 125, m12 -> 500, TanBeta -> 10, SignMu -> 1, Azero -> 0 },
  fdSettings -> { minBRtoPrint -> 1*^-5, maxHigherOrderCorrections -> 4, alphaThomson -> 1, offShellVV -> 2 }
];

The meaning of symbols in fdSettings is the same as options in the FlexibleDecay block (as explained in the previous section). After computing the spectrum via

FSCMSSMCalculateSpectrum[handle];

Decays can be computed as

FSCMSSMCalculateDecays[handle];

Example output

SLHA

Block DCINFO
    1   FlexibleSUSY
    2   2.6.0
    5   SM
    9   4.14.3
DECAY        25     4.01909364E-03   # hh decays
    5.88154048E-01   2          -5         5  # BR(hh -> barFd(3) Fd(3))
    2.04644925E-01   2         -24        24  # BR(hh -> conjVWp VWp)
    8.64458085E-02   2          21        21  # BR(hh -> VG VG)
    6.21678883E-02   2         -15        15  # BR(hh -> barFe(3) Fe(3))
    2.84471939E-02   2          -4         4  # BR(hh -> barFu(2) Fu(2))
    2.59621707E-02   2          23        23  # BR(hh -> VZ VZ)
    2.25173904E-03   2          22        22  # BR(hh -> VP VP)
    1.44211112E-03   2          22        23  # BR(hh -> VP VZ)
    2.63348187E-04   2          -3         3  # BR(hh -> barFd(2) Fd(2))
    2.20054695E-04   2         -13        13  # BR(hh -> barFe(2) Fe(2))

The output conforms to the SLHA standard.

LibraryLink

{
  SM -> {
    hh -> {
      25, 0.00198076, {
        {25, {-15,15}, 0.000157635},
        {25, {23,23},  3.16863*10^-7},
        {25, {-24,24}, 1.14636*10^-6},
        {25, {-3,3},   7.44681*10^-7},
        {25, {22,22},  1.8801*10^-6},
        {25, {-13,13}, 5.58985*10^-7},
        {25, {-5,5},   0.00164052},
        {25, {-4,4},   0.0000812031},
        {25, {21,21},  0.0000967487}
      }
    }
  }
}

At the top of the block we get a PDG id of particle whose with we are computing as well as its total width. The output for every channel, e.g.

{25, {-15,15}, 0.000157635}

contains PDG identifiers for in and out particles and a partial width in GeV.