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pSPSS
: Phenomenological symmetry protected seesaw
The motivation and implementation of the pSPSS
discussed in
- Antusch, J. Hajer, and J. Rosskopp. ‘Simulating heavy neutrino-antineutrino oscillations at colliders’ (2022).
Model description
The pSPSS
describes the interactions of a pseudo-Dirac pair of two Majorana degrees of freedom $N_1$
$N_2$
In the lepton number conserving (LNC) limit the interactions of the symmetry protected seesaw (SPSS) with the Standard Model are
$\mathcal L_\text{SPSS}^L = i \overline N_i \, \not\! \partial N_i - y_{\alpha1} \widetilde H^\dagger \bar \ell_\alpha N_1^c - \overline N_1 m_M^{} N_2^c + \text{H.c.}$
The additional lepton number violating (LNV) interactions must be small in order to generate light neutrino masses.
Additionally, they introduce a mass splitting $\Delta m$
$m_{4/5}^{} = m_M^{} + \frac12 m_M^{} |\theta|^2 \mp \frac12 \Delta m$
where $\theta = m_D / m_M$
$m_D = y_1 v$
$v\simeq174 \text{ GeV}$
The smallness of the lepton number violating interactions ensures unobservable collider effects, with the exception of heavy neutrino-antineutrino oscillations since these are a macroscopic interference effect
$P^{\text{LNC}/\text{LNV}}_\text{osc}(\tau) = (1 \pm \cos\left(\Delta m \tau \right) \exp(-\lambda))/2$
where $\lambda$
FeynRules implementation
The FeynRules model file contains as free parameter in addition to the Standard Model parameter
- Heavy neutrino Yukawa couplings
$y_1$
yvn1
,yvn2
,yvn3
- Majorana mass
$m_M$
Mmaj
- Mass splitting
$\Delta M$
deltaM
- Decoherence damping parameter
$\lambda$
damping
MadGraph patch
In order to generate events with heavy neutrino-antineutrino oscillations it is necessary to patch the ./bin/internal/common_run_interface.py
file in MadGraph using
for event in lhe: leptonnumber = 0 write_event = True for particle in event: if particle.status == 1: if particle.pid in [11, 13, 15]: leptonnumber += 1 elif particle.pid in [-11, -13, -15]: leptonnumber -= 1 for particle in event: id = particle.pid width = param_card['decay'].get((abs(id),)).value mass splitting = param_card.get_value('FRBLOCK', 1) if width: if id in [8000011, 8000012]: tau0 = random.expovariate(width / cst) if 0.5 * (1 + math.cos(mass splitting * tau0 / cst)) >= random.random(): write_event = (leptonnumber == 0) else: write_event = (leptonnumber != 0) vtim = tau0 * c else: vtim = c * random.expovariate(width / cst) if vtim > threshold: particle.vtim = vtim # write this modify event if write_event: output.write(str(event)) output.write('</LesHouchesEvents>\n') output.close()
Attachments (2)
- pSPSS.fr (27.9 KB ) - added by 10 months ago.
-
pSPSS_UFO.zip
(64.9 KB
) - added by 10 months ago.
UFO folder
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