Relaxation of the composite Higgs little hierarchy

Abstract

We describe a composite Higgs scenario in which a cosmological relaxation mechanism naturally gives rise to a hierarchy between the weak scale and the scale of spontaneous global symmetry breaking. This is achieved through the scanning of sources of explicit global symmetry breaking by a relaxion field during an exponentially long period of inflation in the early universe. We explore this mechanism in detail in a specific composite Higgs scenario with QCD-like dynamics, based on an ultraviolet SU(N ) TC 'technicolor' confining gauge theory with three Dirac technifermion flavors. We find that we can successfully generate a hierarchy of scales ξ ≡ h 2 /F 2 π 1.2 × 10 −4 (i.e., compositeness scales F π ∼ 20 TeV) without tuning. This evades all current electroweak precision bounds on our (custodial violating) model. While directly observing the heavy composite states in this model will be challenging, a future electroweak precision measurement program can probe most of the natural parameter space for the model. We also highlight signatures of more general composite Higgs models in the cosmological relaxation framework, including some implications for flavor and dark matter.

Higgs relaxation after inflation

“…Instead, one predicts at least one very light and very weakly interacting particle. This very change of paradigm has therefore far-reaching implications for strategies to search for new physics linked to the understanding of the weak scale and has consequently triggered a large literature: On general model building concerns [2][3][4][5][6][7][8], on attempts to do this without inflation [9,10], on issues related to inflation [11][12][13][14][15][16] and reheating [17], on UV completions involving supersymmetry [15,18,19], composite Higgs [20][21][22], two-Higgs-doublet models [23], a mirror copy of the Standard Model [24], a Nelson-Barr model [25], clockwork axions [26][27][28], warped extra dimensions [29] or other constructions with multiple axions [30], on phenomenological aspects and experimental signatures [31][32][33][34], and on alternative implementations of the mechanism that do not require any barriers [35,36].…”

“…The plotted time evolution is limited to a range where numerics is under control (shortly after t c , fields are subject to a large oscillatory behaviour). This is enough to see that the relaxion slows down and φ stops growing, as soon as 20) which is when some k modes becomes tachyonic (ω 2 k+ < 0), stabilising the Higgs mass parameter, while the temporary additional contribution to the Higgs mass parameter from the gauge field production grows.…”

Fast-rolling relaxion

“…21 The other possibility corresponds to the other edge of the resonance band. 22 The signs of α 1 , β 1 and β 2 do not affect the result.…”

Relaxion and light (pseudo)scalars at the HL-LHC and lepton colliders

“…See Refs. [35][36][37] for attempts in UV completing relaxion models by supersymmetry and composite Higgs. During its evolution, the relaxion scans the Higgs mass parameter µ 2 (φ) from a large and positive cutoff energy Λ 2 down to negative values because of the slow-roll potential…”