Michael Savoy

Upper bounds on sparticle masses from naturalness or how to disprove weak scale supersymmetry

While it is often stated that the notion of electroweak (EW) naturalness in supersymmetric models is subjective, fuzzy and model-dependent, here we argue the contrary: electroweak naturalness can be elevated to a {\it principle} which is both objective and predictive. We demonstrate visually when too much fine-tuning sets in at the electroweak scale which corresponds numerically to the measure \Delta_{BG}~\Delta_{EW}> 30. While many constrained SUSY models are already excluded by this value, we derive updated upper bounds on sparticle masses within the two-extra parameter non-universal Higgs model (NUHM2). We confirm the classic Barbieri-Giudice (BG) result that \Delta_{BG}<30 implies mu <350 GeV. However, by combining dependent soft terms which appear as multiples of m_{3/2} in supergravity models, then we obtain m(gluino)< 4 TeV as opposed to the BG result that m(gluino)<350 GeV. We compare the NUHM2 results to a similar scan in the pMSSM with 19 weak scale parameters. In the pMSSM with complete one-loop scalar potential plus dominant two-loop terms, then a m(gluino)<7 TeV bound is found. Our tabulation of upper bounds provides a target for experimenters seeking to discover or else falsify the existence of weak scale supersymmetry. In an Appendix, we show contributions to the naturalness measure from one-loop contributions to the weak scale scalar potential.

Supergravity gauge theories strike back: There is no crisis for SUSY but a new collider may be required for discovery

More than 30 years ago, Arnowitt-Chamseddine-Nath (ACN) and others established the compelling framework of supergravity gauge theories (SUGRA) as a picture for the next step in beyond the Standard Model physics. We review the current SUGRA scenario in light of recent data from LHC8 collider searches and the Higgs boson discovery. While many SUSY and non-SUSY scenarios are highly disfavored or even excluded by LHC, the essential SUGRA scenario remains intact and as compelling as ever. For naturalness, some non-universality between matter and Higgs sector soft terms is required along with substantial trilinear soft terms. SUSY models with radiatively-driven naturalness (RNS) are found with high scale ne-tuning at a modest 10%. In this case, natural SUSY might be discovered at LHC13 but could also easily elude sparticle search endeavors. A linear e + e collider with p s > 2m(higgsino) is needed to provide the denitive search for the required light higgsino states which are the hallmark of natural SUSY. In the most conservative scenario, we advocate inclusion of a Peccei-Quinn sector so that dark matter is composed of a WIMP/axion admixture i.e. two dark matter particles.

Supersymmetry with Radiatively-Driven Naturalness: Implications for WIMP and Axion Searches

By insisting on naturalness in both the electroweak and quantum chromodynamics (QCD) sectors of the minimal supersymmetric standard model (MSSM), the portrait for dark matter production is seriously modified from the usual weakly interacting massive particle (WIMP) miracle picture. In supersymmetry (SUSY) models with radiatively-driven naturalness (radiative natural SUSY or radiative natural SUSY (RNS)) which include a Dine–Fischler–Srednicki–Zhitnitsky (DFSZ)-like solution to the strong charge-conjugation-parity (CP) and SUSY \(\mu\) problems, dark matter is expected to be an admixture of both axions and higgsino-like WIMPs. The WIMP/axion abundance calculation requires simultaneous solution of a set of coupled Boltzmann equations which describe quasi-stable axinos and saxions. In most of parameter space, axions make up the dominant contribution of dark matter although regions of WIMP dominance also occur. We show the allowed range of Peccei-Quinn (PQ) scale \(f_a\) and compare to the values expected to be probed by the axion dark matter search experiment (ADMX) axion detector in the near future. We also show WIMP detection rates, which are suppressed from usual expectations, because now WIMPs comprise only a fraction of the total dark matter. Nonetheless, ton-scale noble liquid detectors should be able to probe the entirety of RNS parameter space. Indirect WIMP detection rates are less propitious since they are reduced by the square of the depleted WIMP abundance.

What hadron collider is required to discover or falsify natural supersymmetry

Abstract Weak scale supersymmetry (SUSY) remains a compelling extension of the Standard Model because it stabilizes the quantum corrections to the Higgs and W , Z boson masses. In natural SUSY models these corrections are, by definition, never much larger than the corresponding masses. Natural SUSY models all have an upper limit on the gluino mass, too high to lead to observable signals even at the high luminosity LHC. However, in models with gaugino mass unification, the wino is sufficiently light that supersymmetry discovery is possible in other channels over the entire natural SUSY parameter space with no worse than 3% fine-tuning. Here, we examine the SUSY reach in more general models with and without gaugino mass unification (specifically, natural generalized mirage mediation), and show that the high energy LHC (HE-LHC), a pp collider with s = 33 TeV, will be able to detect the SUSY signal over the entire allowed mass range. Thus, HE-LHC would either discover or conclusively falsify natural SUSY with better than 3% fine-tuning using a conservative measure that allows for correlations among the model parameters.

Multichannel assault on natural supersymmetry at the high luminosity LHC

Recent clarifications of naturalness in supersymmetry robustly require the presence of four light higgsinos with mass ~100-300 GeV while gluinos and (top)-squarks may lie in the multi-TeV range, possibly out of LHC reach. We project the high luminosity (300-3000 fb^{-1}) reach of LHC14 via gluino cascade decays and via same-sign diboson production. We compare these to the reach for neutralino pair production \tz_1\tz_2 followed by \tz_2\to\tz_1\ell^+\ell^- decay to soft dileptons which recoil against a hard jet. It appears that 3000 fb^{-1} is just about sufficient integrated luminosity to probe naturalness with up to 3\% fine-tuning at the 5-sigma level, thus either discovering natural supersymmetry or else ruling it out.

Superparticle phenomenology from the natural mini-landscape

A bstractThe methodology of the heterotic mini-landscape attempts to zero in on phenomenologically viable corners of the string landscape where the effective low energy theory is the Minimal Supersymmetric Standard Model with localized grand unification. The gaugino mass pattern is that of mirage-mediation. The magnitudes of various SM Yukawa couplings point to a picture where scalar soft SUSY breaking terms are related to the geography of fields in the compactified dimensions. Higgs fields and third generation scalars extend to the bulk and occur in split multiplets with TeV scale soft masses. First and second generation scalars, localized at orbifold fixed points or tori with enhanced symmetry, occur in complete GUT multiplets and have much larger masses. This picture can be matched onto the parameter space of generalized mirage mediation. Naturalness considerations, the requirement of the observed electroweak symmetry breaking pattern, and LHC bounds on mg together limit the gravitino mass to the m3/2 ∼ 5-60 TeV range. The mirage unification scale is bounded from below with the limit depending on the ratio of squark to gravitino masses. We show that while natural SUSY in this realization may escape detection even at the high luminosity LHC, the high energy LHC with s=33

Generalized focus point and mass spectra comparison of highly natural SUGRA GUT models

\sqrt{s}=33

Gluino reach and mass extraction at the LHC in radiatively-driven natural SUSY

TeV could unequivocally confirm or exclude this scenario. It should be possible to detect the expected light higgsinos at the ILC if these are kinematically accessible, and possibly also discriminate the expected compression of gaugino masses in the natural mini-landscape picture from the mass pattern expected in models with gaugino mass unification. The thermal WIMP signal should be accessible via direct detection searches at the multi-ton noble liquid detectors such as XENONnT or LZ.