Dark Matter Processes

  1. Scalar Mediator
  2. Vector Mediator Z'
  3. Drell-Yan production of charged co-annihilation partners
This page contains the production of Dirac fermion Dark Matter via new s-channel mediators. A summary of the physics scenarios and parameters involved can be found in [Des18]. Examples how these processes can be run are found in main75.cc and main76.cc.

The particles in the scenarios considered here are a mix of established PDG ones (51 - 55) and extensions thereof ( 56 - 59), as follows:
51Scalar DM (currently unused);
52Fermionic DM (chi_1);
53Vector DM (currently unused);
54Scalar (or pseudoscalar) mediator (S);
55Vector (or axial vector) mediator (Z');
56Charged scalar partner (l^~);
57Singly charged partner (chi^+);
58Neutral partner (chi_2);
59Doubly charged partner (chi^++).

Scalar Mediator

flag  DM:gg2S2XX   (default = off)
Scattering g g → S → X Xbar. Code 6011. S is assumed to be on-shell.

flag  DM:gg2S2XXj   (default = off)
Scattering g g →S → X Xbar j. Code 6012. S is assumed to be on-shell. (Not yet available.)

Fermion couplings to scalar S are assumed to be proportional to mass of the fermion and couplings are the factor multiplying SM Higgs coupling (i.e. sin(mixing) in case of portal models).

parm  Sdm:vf   (default = 0.1)
Scalar coupling of SM fermions.

parm  Sdm:af   (default = 0)
Pseudo-scalar coupling of SM fermions.

parm  Sdm:vX   (default = 1.0)
Scalar coupling of DM fermion.

parm  Sdm:aX   (default = 0)
Pseudo-scalar coupling of DM fermion.

Vector Mediator Z'

The Vector mediator model assumes a simplified U(1) model with couplings to fermionic Dark Matter. Both vector and axial couplings are possible. Interference with gamma/Z is currently not implemented, therefore this should mainly be used when Z' → X Xbar. However, a quick check of dijet or dilepton cross sections can be made by setting the mode Zp:decayMode.

mode  Zp:decayMode   (default = 0; minimum = 0; maximum = 3)
Switch to change decay of the Z'.
option 0 : X Xbar
option 1 : q qbar (dijets)
option 2 : l lbar (charged dileptons)
option 3 : nu nubar + X Xbar (invisible)

flag  DM:ffbar2Zp2XX   (default = off)
Scattering f fbar →Z'^0 → X Xbar. Code 6001. Z' is assumed to be on-shell.

flag  DM:ffbar2ZpH   (default = off)
Scattering f fbar →Z'^0 H . Code 6004. Z' is assumed to be on-shell. The coupling of the Z' to the SM Higgs is given by the parameter Zp:coupH. Interference with gamma/Z currently not implemented therefore this is only suitable when Z' → X Xbar. This can be ensured using
55:onMode = off
55:onIfAny = 52

flag  DM:ffbar2Zp2XXj   (default = off)
Scattering f fbar →Z'^0 j → X Xbar j. Code 6002. Z' is assumed to be on-shell. (Not yet available.)

flag  DM:qg2Zp2XXj   (default = off)
Scattering q g →Z'^0 j → X Xbar j. Code 6003. Z' is assumed to be on-shell. (Not yet available.)

The vector and axial couplings of fermionic DM to the Z'^0 can be set freely. The couplings of quarks and leptons can either be chosen freely for a new U(1) or be given by kinetic mixing with the SM U(1)_Y. The SM fermion couplings are assumed to be universal, i.e. generation-independent. The choice of fixed axial and vector couplings implies a resonance width that increases linearly with the Z' mass. Also some overall coupling strengths can be chosen freely.

parm  Zp:vX   (default = 1.)
Vector coupling of DM fermion.

parm  Zp:aX   (default = 0.)
Axial coupling of DM fermion.

flag  Zp:kineticMixing   (default = off)
Flag for the two main options to set the couplings of the Z' to SM quarks and leptons. In the default off option the overall coupling strength of the new U(1) gauge group is given by Zp:gZp and the separate fermion couplings by Zp:vu through Zp:av. In the alternative, with kinetic mixing on, the coupling to the DM is still given by Zp:gZp, but the mixing parameter Zp:epsilon now specifies how the separate fermion couplings are related to their U(1)_Y values.

parm  Zp:gZp   (default = 0.1)
Gauge coupling of a new U(1). This parameter also sets the coupling of the DM to the Z', whether kinetic mixing is on or not.

parm  Zp:vu   (default = 1.)
Vector coupling of up-type quarks.

parm  Zp:au   (default = 0.)
Axial coupling of up-type quarks.

parm  Zp:vd   (default = 1.)
Vector coupling of down-type quarks.

parm  Zp:ad   (default = 0.)
Axial coupling of down-type quarks.

parm  Zp:vl   (default = 1.)
Vector coupling of charged leptons.

parm  Zp:al   (default = 0.)
Axial coupling of charged leptons.

parm  Zp:vv   (default = 1.)
Vector coupling of neutrinos.

parm  Zp:av   (default = 0.)
Axial coupling of neutrinos.

parm  Zp:epsilon   (default = 0.1)
Kinetic mixing parameter between the dark U(1) and the SM hypercharge U(1). In the implemented case the Z'^0 mass is larger than the SM Z^0 one. The fermionic current for Z'^0 is described in [Cli184].

parm  Zp:coupH   (default = 0.1)
Coupling to the SM higgs when kinetic mixing is off. When on the coupling is instead set by Zp:epsilon.

Drell-Yan production of charged co-annihilation partners

We implement two models of co-annihilating Dark Matter where the co-annihilation partner carries EW charge and therefore can be produced via Drell-Yan production. The underlying model and production process can be selected by choosing the parameter DM:DYtype.

The first model consists of co-annihilation with a scalar with leptonic quantum numbers and which couples to a right-handed SM lepton and a Dirac fermion Dark Matter via Yukawa couplings. It is possible to choose lepton flavour violating couplings.

The next model is a generalisation of the mixed gaugino sector of Supersymmetry parametrised by one SM singlet and one SU(2) N-plet which mix to form Dark matter. N = 2, 3 and 5 are supported by the code. The main motivation for this choice is to provide a fully flexible implementation to calculate production of long-lived particles at the LHC. The resultant spectrum consists of one neutral partner, one singly charged partner, and one doubly charged partner (in the case of the 5-plet). The only free parameters are masses of the singlet and N-plet and the mixing suppression scale. This determines both production and decay of the particles and can cover a range of signatures including displaced leptons and vertices, long-lived, kinked or disappearing tracks.

flag  DM:qqbar2DY   (default = off)
Scattering q qbar → X_i Xbar_i . Code 6020.

mode  DM:DYtype   (default = 1; minimum = 1; maximum = 4)
Select the co-annihilation partner to produce via Drell-Yan production.
option 1 : Scalar lepton production. Coupling to electrons, muons and taus can be fixed by DM:yuk1, DM:yuk2, and DM:yuk3 respectively.
option 2 : Production of charged partners (i.e. "charginos").
option 3 : Production of doubly charged partners.
option 4 : Production of neutral and singly-charged partners.

The Yukawa couplings can be set using

parm  DM:yuk1  
Electron-DM Yukawa.

parm  DM:yuk2  
Muon-DM Yukawa.

parm  DM:yuk3  
Tau-DM Yukawa.

The parameters for the singlet-N-plet model can be set via the following:

mode  DM:Nplet   (default = 2; minimum = 1; maximum = 3)

option 1 : Doublet
option 2 : Triplet
option 3 : Quintuplet

parm  DM:M1  
Mass of the DM singlet state.

parm  DM:M2  
Mass of the DM N-plet state.

parm  DM:Lambda  
The suppression scale of the mixing. The Wilson co-efficient is absorbed into the suppression scale as there is no independent measurement to disentangle it from the scale.