Split supersymmetry

Abstract

The naturalness criterion applied to the cosmological constant implies a new-physics threshold at 10 −3 eV. Either the naturalness criterion fails, or this threshold does not influence particle dynamics at higher energies. It has been suggested that the Higgs naturalness problem may follow the same fate. We investigate this possibility and, abandoning the hierarchy problem, we use unification and dark matter as the only guiding principles. The model recently proposed by Arkani-Hamed and Dimopoulos emerges as a very interesting option. We study it in detail, analysing its structure, and the conditions for obtaining unification and dark matter. the anthropic principle [1], which could be operating in presence of a large number of metastable vacua, as in string theory [2].It is conceivable to ponder whether such an explanation could also apply to the hierarchy problem, imagining a mechanism (not necessarily based on the anthropic principle) which allows to extrapolate SM calculations to energies much larger than the TeV, without the need of introducing new dynamics, besides the Higgs.At first sight, this sounds like a devastating proposal. But, if we are willing to abandon the hierarchy problem, we can try to use other clues to drive the search for the theory beyond the SM. Gauge coupling unification could be one such clue: it is motivated by a theory that addresses questions related to the fundamental structure of the SM particle content.The failure of exact unification of gauge couplings in the SM suggests the existence of new particles, belonging to incomplete GUT irreps, which mend the mismatch. It is well known that low-energy supersymmetry provides precisely the necessary particles with the appropriate quantum numbers. Recently, Arkani-Hamed and Dimopoulos [3], setting aside the hierarchy problem, have noticed that gauge-coupling unification can be achieved in a supersymmetric model where all scalars, but one Higgs doublet, are much heavier than the electroweak scale. Most of the unpleasent aspects of supersymmetry (excessive flavour

MWand sin2θeffin split SUSY: present and future expectations

“…Recently, the scenario of Split SUSY has been suggested [5][6][7]. In this scenario, the SUSY-breaking scale is much heavier than the electroweak scale, i.e.…”

“…It is already known that the strong constraints on the parameters of low-energy SUSY imposed by the lower bound on the Higgs-boson mass, m H > 114.4 GeV [17], are relaxed in Split SUSY. This is thanks to the large corrections to this mass, due to the renormalization group evolution from the scale of heavy scalars to the weak scale [6]. These effects have been taken into account in our analysis by using the renormalization group evolution as given in Ref.…”

“…These effects have been taken into account in our analysis by using the renormalization group evolution as given in Ref. [6].…”

“…The Higgs-boson mass is computed according to Ref. [6] for Split SUSY, and using the leading m t , m b tan β approximation for the MSSM [21]. The Split SUSY/MSSM contributions to ∆r are added to the ZFITTER computation, and we proceed in an iterative way to compute M W , sin 2 θ W .…”

“…The most important phenomenological consequence of Split SUSY is the presence of a long-lived gluino [5,6,25,26]. The scalar mass scale (m) lays between the EW scale (∼ 1 TeV) and the unification scale (∼ 10 16 GeV), current limits from gluino cosmology set an upper boundm 10 9 GeV [26].…”