Low-scale neutrino seesaw mechanism and scalar dark matter

Abstract

We discuss how two birds-the little hierarchy problem of low-scale type-I seesaw models and the search for a viable dark matter candidate-are (proverbially) killed by one stone: a new inert scalar state. MotivationsTogether with the presence of dark matter (DM), neutrino oscillations-and the small neutrino mass entailed-are the only physics beyond the standard model (SM) experimentally confirmed.The most attractive model to account for the smallness of the neutrino masses is the seesaw mechanism [1][2][3][4]. This mechanism requires right-handed (RH) neutrinos whose masses can be taken at the GUT scale or, in low-scale scenarios, at lower energies if the Yukawa couplings are taken proportionally smaller, for instance, of the order of those of the charged leptons.The inclusion of these new states within the SM induces a finite renormalization that tends to pull the Higgs boson mass (or, equivalently, the electroweak (EW) scale) toward the higher scale. This is not a problem if the new states are themselves at the EW scale and the renormalization is itself of the order of the Higgs boson mass. If instead the new states are at a larger scale, they give rise to a hierarchy problem in which in order to keep the Higgs boson mass to its experimental value we have to cancel the renormalization to the higher scale to a degree that becomes increasingly fine-tuned as the new states are taken at higher mass scales.Such a cancelation can be achieved by a redefinition of the Higgs boson bare mass but it is more appealing and practical to use the hierarchy problem in a heuristic manner to help us in the definition of whatever model of physics we assume to exist beyond the SM [5]. a e-mail: marco@sissa.itThe problem of the large contribution to the Higgs mass m H coming from the new states is best understood in terms of the renormalization group equation (RGE)where the anomalous dimension is given, at one-loop order, byin dimensional regularization and where we only wrote the dominant contributions from the Higgs boson potential (λ), the top quark (λ t ) and the gauge couplings (g 1 and g 2 ). If new states are present at a higher scale, they must be introduced as a threshold effect in order to match the low-and highscale effective theories. That these threshold corrections are larger and larger as the new states are taken to be heavier and heavier is the hierarchy problem in the framework of an effective theory. According to the proposed approach, the new stateswhen they are taken together-must enter in such a way that their overall effect on the Higgs boson mass renormalization is no larger than the EW scale, thus making the bare mass renormalization natural. In other words, using the RGE terminology, the threshold corrections must be small and if the new states are very heavy they must enter in such a way as to cancel their respective contributions.The fine-tuning, if present, is all among the new states rather than between them and the SM contributions. In this approach it is possible to keep the physics at the two ...

Towards completing the standard model: Vacuum stability, electroweak symmetry breaking, and dark matter

“…However, we feel that it is also worthwhile and necessary to study different approaches to addressing the SM problems. Recently it has been re-emphasised by several groups [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] that the physical naturalness argument [30], motivated by the apparent absence of particle threshold corrections to the cosmological constant and to the mass of the Higgs boson, allows several possibilities of formulating new physics scenarios. In this work we start with the SM and use the principle of minimality to formulate a logically consistent view on the SM and on its potential extensions.…”

Radiative neutrino mass model from a mass dimension-11 ∆L = 2 effective operator

“…The three seesaw models [17][18][19][20][21][22][23][24][25], for example, are all UV-completions of the same mass-dimension 5 effective operator, called the Weinberg operator. The seesaw models are wonderfully minimal, however the high BSM scale typically invoked makes them challenging to experimentally test [26][27][28]. We should, therefore, consider other possibilities, for this reason, as well as for the sake of completeness.…”

Transverse momentum resummation for t -channel single top quark production at the LHC

“…At the CERN Large Hadron Collider (LHC), top quarks can be produced by the electroweak gauge interaction [1][2][3][4]. Its cross section is proportional to the W tb coupling [5][6][7][8][9][10][11][12][13][14][15][16][17][18] and Cabibbo-Kobayashi-Maskawa (CKM) matrix element V tb [9,19]. Hence, it offers a promising way to constrain various W tb anomalous couplings, induced by NP, or determine V tb without assuming the generation of quarks.…”