Improving naturalness in gauge mediation with nonunified messenger sectors

Abstract

We study models of gauge-mediated supersymmetry breaking with messengers that do not belong to complete representations of grand-unified gauge groups. We show that certain setups characterized by heavy Wino can greatly improve the fine tuning with respect to models with unified messengers, such as minimal gauge mediation. The typical models with low tuning feature multi-TeV superparticles, with the exception of the Higgsinos and possibly Bino and right-handed sleptons. As a consequence, the absence of signals for supersymmetry at the LHC is trivially accommodated in our framework. On the other hand, testing these models will be challenging at the LHC. We finally show that the gravitino can be a consistent candidate for cold dark matter, provided a rather low reheating temperature, if a standard thermal history of the universe is assumed.

Low fine-tuning in Yukawa-deflected gauge mediation

“…In [2], we found that the typical spectra of these low-tuned models with M 2 > M 3 tend to lie in the multi-TeV range (mainly because of m h ), and the only sub-TeV states are the Higgsino and possibly Bino and right-handed sleptons. The absence of signals at the LHC searches is therefore a natural consequence of the framework.…”

“…As in [2], we work in the context of the minimal supersymmetric standard model (MSSM) and we consider a Gauge Mediation setup where SUSY breaking is transmitted to the visible sector trough loops involving heavy messengers in vectorlike representations of the Standard Model (SM) gauge group, which however do not necessarily belong to complete multiplets of a grand unified group. The resulting contributions to gaugino and sfermion masses then depend on three independent parameters b M 1 , b M 2 , b M 3 , denoting the shifts induced at the messenger scale M to the 1-loop β-function coefficients of the SM gauge couplings g 1 , g 2 , g 3 .…”

“…In a previous work [2], we employed the "electro-weak FT", ∆ EW , introduced in [3,4], in order to show that models with gauge-mediated SUSY breaking [5] with messengers in incomplete representations of a grand unified gauge group can lower the FT by more than one order of magnitude with respect to mGMSB, i.e. ∆ EW 50.…”

“…In particular, solutions with a reduced FT are possible if such non-unified messenger sector gives raise to a Wino mass substantially larger than the gluino mass at the mediation scale. This in turn induces a compensation between gauge and Yukawa radiative corrections to the Higgs soft mass m 2 Hu , reducing its sensitivity to stop and gluino masses. This effect can be appreciated by inspecting the renormalization group equation (RGE) of m 2 Hu , whose one-loop expression is: t ≡ log µ M ,…”

“…the fine tuning. At the same time, the A t induced by the matter-messenger coupling should allow to obtain m h 125 GeV with a O(1) TeV stop, unlike in [2].…”