Tuesday, March 26, 2019

A New Scenario For Matter Creation (updated March 27, 2019)

There are very strict experimental bounds on proton decay and neutrinoless double beta decay. These bound mean that these processes can't account for the lepton number and baryon number of the Universe, in a pure energy Big Bang that has zero lepton and baryon number at t=0 scenario, without new physics at much greater than LHC high energies. But, three unit lepton number violation isn't nearly as well studied and might fill gaps that the other processes do not (although I doubt that they will).

The body text notes that: "it is conceivable that lepton number can only be changed in multiples of 3, in which case the signals to look for are different. In fact, this is what happens in the Standard Model since non-perturbative effects can change the net lepton and baryon numbers by 3 units only."

Violation of lepton number in 3 units

The number of leptons may or may not be a conserved quantity. The Standard Model predicts that it is (in perturbative processes), but there is the well known possibility that new physics violates lepton number in one or two units. The first case (
) is associated to proton decay into mesons plus a lepton or an anti-lepton, while the second one (ΔL=2
) is usually associated to Majorana neutrino masses and neutrinoless double beta decay. It is also conceivable that leptons can only be created or destroyed in groups of three (ΔL=3
). Colliders and proton decay experiments can explore this possibility.
Comments:Contribution to the proceedings of the 6th Symposium on Prospects in the Physics of Discrete Symmetries (DISCRETE 2018), Vienna, Austria, 26-30 November 2018
Subjects:High Energy Physics - Phenomenology (hep-ph)
Cite as:arXiv:1903.09675 [hep-ph]
(or arXiv:1903.09675v1 [hep-ph] for this version.
Similar ideas with a body text quotation:

Model-independent upper limits on lepton number violating states from neutrino mass

We propose a model-independent framework to classify and study neutrino mass models and their phenomenology. The idea is to introduce one particle beyond the Standard Model which couples to leptons and carries lepton number together with the lowest-dimensional operator which violates lepton number by two units and contains this particle. The resulting contribution to neutrino masses can be translated to a robust upper bound on the mass of the new particle. We compare it to the stronger but less robust upper bounds from Higgs naturalness and discuss several lower bounds.
Comments:6 pages, 1 table, 1 figure
Subjects:High Energy Physics - Phenomenology (hep-ph)
Report number:SISSA 07/2019/FISI
Cite as:arXiv:1903.10552 [hep-ph]
(or arXiv:1903.10552v1 [hep-ph] for this version)
"We have derived general robust upper bounds on the mass of new particles contributing to neutrino masses. Our main results are summarized in Fig. 1. We have also compared our limits with those from Higgs naturalness, which are much stronger, but less robust. The lower bounds are generally model-dependent. Among these nucleon decays provide the most stringent limits. If V2, V˜ 2, or U1 correspond to SU(5)/SO(10) gauge bosons, they can not be the dominant source of neutrino masses. The most promising particles to search for are new doublycharged scalars which have masses below O(106 ) GeV, if they contribute to neutrino masses. This work is intended to serve not only as an indication of the most promising particles to directly search for at colliders, but also as a simple way of organizing the plethora of neutrino mass models."
And then this:

Two-component Dark Matter with co-genesis of Baryon Asymmetry of the Universe

We discuss the possibility of realising a two-component dark matter (DM) scenario where the two DM candidates differ from each other by virtue of their production mechanism in the early universe. One of the DM candidates is thermally generated in a way similar to the weakly interacting massive particle (WIMP) paradigm where the DM abundance is governed by its freeze-out while the other candidate is produced only from non-thermal contributions similar to freeze-in mechanism. We discuss this in a minimal extension of the standard model where light neutrino masses arise radiatively in a way similar to the scotogenic models with DM particles going inside the loop. The lepton asymmetry is generated at the same time from WIMP DM annihilations as well as partially from the mother particle for non-thermal DM. This can be achieved while satisfying the relevant experimental bounds, and keeping the scale of leptogenesis or the thermal DM mass as low as 3 TeV, well within present experimental reach. In contrast to the TeV scale thermal DM mass, the non-thermal DM can be as low as a few keV, giving rise to the possibility of a sub-dominant warm dark matter (WDM) component that can have interesting consequences on structure formation. The model also has tantalizing prospects of being detected at ongoing direct detection experiments as well as the ones looking for charged lepton flavour violating process like μeγ.
Comments:28 pages, 10 figures
Subjects:High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Cite as:arXiv:1903.10516 [hep-ph]
 (or arXiv:1903.10516v1 [hep-ph] for this version)

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