Very light dilaton and naturally light Higgs boson

Abstract

We study very light dilaton, arising from a scale-invariant ultraviolet theory of the Higgs sector in the standard model of particle physics. Imposing the scale symmetry below the ultraviolet scale of the Higgs sector, we alleviate the fine-tuning problem associated with the Higgs mass. When the electroweak symmetry is spontaneously broken radiativelyà la Coleman-Weinberg, the dilaton develops a vacuum expectation value away from the origin to give an extra contribution to the Higgs potential so that the Higgs mass becomes naturally around the electroweak scale. The ultraviolet scale of the Higgs sector can be therefore much higher than the electroweak scale, as the dilaton drives the Higgs mass to the electroweak scale. We also show that the light dilaton in this scenario is a good candidate for dark matter of mass m D ∼ 1 eV − 10 keV, if the ultraviolet scale is about 10−100 TeV. Finally we propose a dilaton-assisted composite Higgs model to realize our scenario. In addition to the light dilaton the model predicts a heavy U(1) axial vector boson and two massive, oppositely charged, pseudo Nambu-Goldstone bosons, which might be accessible at LHC.

Sp (4) gauge theories on the lattice: Nf = 2 dynamical fundamental fermions

“…Particular attention has been devoted to models and dynamical theories characterised by the SU (4)/Sp(4) coset (see for instance Refs. [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59]). The low-energy EFT Lagrangian contains, in this case, five scalar fields, that describe the long-distance dynamics of the five pNGBs.…”

Into the conformal window: Multirepresentation gauge theories

“…The other common non-trivial features of near-conformal gauge theories are the emergence of a light scalar resonance. Such a new degree of freedom at low energy may be identified as a dilaton arising from the spontaneous breaking of scale symmetry, and can be used to extend the Higgs sector of the standard model of particle physics [31][32][33][34][35][36][37][38][39][40][41]. Interestingly, recent lattice studies of SU (3) gauge theories with 8 fundamental Dirac fermions [42][43][44][45], as well as 2 two-index symmetric Dirac fermions [46][47][48][49][50], performed with moderate sizes of the fermion mass found a relatively light scalar in the spectrum.…”

Holographic light dilaton at the conformal edge

“…The background solution should not cross the nodes of the sine function in z UV ≤ z ≤ z IR for smoothness and stability of the solution. 1 Thus we may parametrize…”

“…The action W (1) is UV divergent, and holographic renormalization is required. It is well known how generic Einstein-scalar actions are renormalized (see [35] for a thorough discussion).…”

“…Why the Higgs mass is so light compared to the fundamental scale of elementary particles, like the Planck or GUT scales, has been one of the driving questions for physics beyond the standard model, as the Higgs mass in the standard model is seemingly extremely fine-tuned. Much of interest on naturally light Higgs has been focused recently on dynamically generating Higgs mass from quantum criticality or conformal edge, at which the BSM physics enjoys the scale invariance at high energies (UV) [1,2]. This approach of explaining Higgs mass from conformal edge turns out to be quite attractive in view of current experimental status of not finding any hint of new particles around the weak scale, Λ ew ∼ 1 TeV, that has been explored vigorously at current energy frontiers.…”