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 i
n 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 fine-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 sqrt{s}>2m(higgsino) is needed to provide the definitive 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.
Recently, it has been argued that various measures of SUSY naturalness-- electroweak, Higgs mass and EENZ/BG-- when applied consistently concur with one another and make very specific predictions for natural supersymmetric spectra. Highly natural spe
ctra are characterized by light higgsinos with mass not too far from m_h and well-mixed but TeV-scale third generation squarks. We apply the unified naturalness measure to the case of heavy Higgs bosons A, H and H^pm. We find that their masses are bounded from above by naturalness depending on tan(beta): e.g. for 10% fine-tuning and tan(beta)~ 10, we expect m_A< 2.5 TeV whilst for 3% fine-tuning and tan(beta) as high as 50, then m_A< 8 TeV. Furthermore, the presence of light higgsinos seriously alters the heavy Higgs boson branching ratios, thus diminishing prospects for usual searches into Standard Model (SM) final states, while new discovery possibilities arise due to the supersymmetric decay modes. The heavy SUSY decay modes tend to be H, A, H^pm-> W, Z, or h+MET + soft tracks so that single heavy Higgs production is characterized by the presence of high p_T W, Z or h bosons plus missing E_T. These new heavy Higgs boson signatures seem to be challenging to extract from SM backgrounds.
Radiatively-driven natural supersymmetry (RNS) potentially reconciles the Z and Higgs boson masses close to 100 GeV with gluinos and squarks lying beyond the TeV scale. Requiring no large cancellations at the electroweak scale in constructing M_Z=91.
2 GeV while maintaining a light Higgs scalar with m_h 125 GeV implies a sparticle mass spectrum including light higgsinos with mass 100-300 GeV, electroweak gauginos in the 300-1200 GeV range, gluinos at 1-4 TeV and top/bottom squarks in the 1-4 TeV range (probably beyond LHC reach), while first/second generation matter scalars can exist in the 5-30 TeV range (far beyond LHC reach). We investigate several characteristic signals for RNS at LHC14. Gluino pair production yields a reach up to m_{tg} 1.7 TeV for 300 fb^{-1}. Wino pair production -- pptotw_2tz_4 and tw_2tw_2 -- leads to a unique same-sign diboson (SSdB) signature accompanied by modest jet activity from daughter higgsino decays; this signature provides the best reach up to m_{tg} 2.1 TeV within this framework. Wino pair production also leads to final states with (WZto 3ell)+eslt as well as 4ell+eslt which give confirmatory signals up to m_{tg} 1.4 TeV. Directly produced light higgsinos yield a clean, soft trilepton signature (due to very low visible energy release) which can be visible, but only for a not-too-small a tz_2-tz_1 mass gap. The clean SSdB signal -- as well as the distinctive mass shape of the dilepton mass distribution from tz_{2,3}totz_1ellell decays if this is accessible -- will mark the presence of light higgsinos which are necessary for natural SUSY. While an e^+e^- collider operating with sqrt{s} 600 GeV should unequivocally reveal the predicted light higgsinos, the RNS model with m_{1/2}> 1 TeV may elude all LHC14 search strategies even while maintaining a high degree of electroweak naturalness.
The International Linear Collider Technical Design Report (TDR) describes in four volumes the physics case and the design of a 500 GeV centre-of-mass energy linear electron-positron collider based on superconducting radio-frequency technology using N
iobium cavities as the accelerating structures. The accelerator can be extended to 1 TeV and also run as a Higgs factory at around 250 GeV and on the Z0 pole. A comprehensive value estimate of the accelerator is give, together with associated uncertainties. It is shown that no significant technical issues remain to be solved. Once a site is selected and the necessary site-dependent engineering is carried out, construction can begin immediately. The TDR also gives baseline documentation for two high-performance detectors that can share the ILC luminosity by being moved into and out of the beam line in a push-pull configuration. These detectors, ILD and SiD, are described in detail. They form the basis for a world-class experimental programme that promises to increase significantly our understanding of the fundamental processes that govern the evolution of the Universe.
Imposing electroweak scale naturalness constraints (low Delta_{EW}) on SUSY models leads to mass spectra characterized by light higgsinos ~100-300 GeV, highly mixed top-squarks and gluinos at the 1-5 TeV scale and allows for m_h ~125 GeV. First and s
econd generation squarks can easily live at the 5-20 TeV scale, thus providing at least a partial solution to the SUSY flavor/CP problems. For such models at the LHC, gluino pair production is followed by cascade decays to t- and b-quark rich final states along with multileptons. The reach of LHC14 with 300 fb^{-1} is computed to be around m_{tg} 1.8 TeV. However, the small magnitude of the mu-parameter-- a necessary condition for naturalness-- leads to a unique hadronically quite same-sign diboson (W^pm W^pm) signature from wino pair production. In low Delta_{EW} models with unified gaugino masses, this signature yields a somewhat higher reach up to m_{tg} 2.1 TeV. The smallness of |mu| implies that the ILC should be a higgsino factory in addition to a Higgs factory, and a complete search for SUSY naturalness seems possible for sqrt{s} 600 GeV. Since a thermal under-abundance of higgsino-like WIMP dark matter (DM) is expected, there is ample room for an axion DM contribution. A thorough search for higgsino-like WIMPs can be made by next generation WIMP detectors, such as those with ton-scale noble liquid targets.
In supersymmetric models with light higgsinos (which are motivated by electroweak naturalness arguments), the direct production of higgsino pairs may be difficult to search for at LHC due to the low visible energy release from their decays. However,
the wino pair production reaction tw_2^pmtz_4to (W^pmtz_{1,2})+(W^pmtw_1^mp) also occurs at substantial rates and leads to final states including equally opposite-sign (OS) and same-sign (SS) diboson production. We propose a novel search channel for LHC14 based on the SS diboson plus missing E_T final state which contains only modest jet activity. Assuming gaugino mass unification, and an integrated luminosity > 100 fb^{-1}, this search channel provides a reach for SUSY well beyond that from usual gluino pair production.
In SUSY models with heavy squarks and gaugino mass unification, the gaugino pair production reaction pp-> tw_1^pmtz_2 dominates gluino pair production for m_{tg}agt 1 TeV at LHC with sqrt{s}=14 TeV (LHC14). For this mass range, the two-body decays tw
_1to Wtz_1 and tz_2to htz_1 are expected to dominate the chargino and neutralino branching fractions. By searching for ell bbar{b}+MET events from tw_1^pmtz_2 production, we show that LHC14 with 100 fb^{-1} of integrated luminosity becomes sensitive to chargino masses in the range m_{tw_1}sim 450-550 GeV corresponding to m_{tg}sim 1.5-2 TeV in models with gaugino mass unification. For 10^3 fb^{-1}, LHC14 is sensitive to the Wh channel for m_{tw_1}sim 300-800 GeV, corresponding to m_{tg}sim 1-2.8 TeV, which is comparable to the reach for gluino pair production followed by cascade decays. The Wh+MET search channel opens up a new complementary avenue for SUSY searches at LHC, and serves to point to SUSY as the origin of any new physics discovered via multijet and multilepton + MET channels.
We investigate the prospects for the discovery of a neutral Higgs boson produced in association with a $b$ quark, followed by the Higgs decay into a pair of bottom quarks, $pp to bphi^0 to b bbar{b} +X$, at the CERN Large Hadron Collider (LHC) within
the framework of unified supersymmetric models. The Higgs boson $phi^0$ can be a heavy scalar $H^0$ or a pseudoscalar $A^0$. Furthermore, this direct discovery channel is compared with the indirect Higgs searches in the rare decay $B_s to mu^+mu^-$ at hadron colliders. Promising results are found for the minimal supergravity (mSUGRA) model, the anomaly mediated supersymmetry breaking (AMSB) model, and the gauge mediated supersymmetry breaking (GMSB) model. We find that the indirect search for $B(B_s to mu^+mu^-) ge 5times 10^{-9}$ is complementary to the direct search for $bphi^0 to bbbar{b}$ with $sqrt{s} = 14$ TeV and an integrated luminosity ($L$) of 300 fb$^{-1}$. In the AMSB and GMSB models, $bphi^0 to bbbar{b}$ with $L = 300$ fb$^{-1}$ covers a larger area in the parameter space than $B(B_s to mu^+mu^-) ge 5times 10^{-9}$. In addition, we present constraints from $b to sgamma$ and muon anomalous dipole moment ($Delta a_mu$) on the parameter space.
We calculate the relic abundance of mixed axion/neutralino cold dark matter which arises in R-parity conserving supersymmetric (SUSY) models wherein the strong CP problem is solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/saxion/a
xino supermultiplet. By numerically solving the coupled Boltzmann equations, we include the combined effects of 1. thermal axino production with cascade decays to a neutralino LSP, 2. thermal saxion production and production via coherent oscillations along with cascade decays and entropy injection, 3. thermal neutralino production and re-annihilation after both axino and saxion decays, 4. gravitino production and decay and 5. axion production both thermally and via oscillations. For SUSY models with too high a standard neutralino thermal abundance, we find the combined effect of SUSY PQ particles is not enough to lower the neutralino abundance down to its measured value, while at the same time respecting bounds on late-decaying neutral particles from BBN. However, models with a standard neutralino underabundance can now be allowed with either neutralino or axion domination of dark matter, and furthermore, these models can allow the PQ breaking scale f_a to be pushed up into the 10^{14}-10^{15} GeV range, which is where it is typically expected to be in string theory models.
We consider supersymmetric (SUSY) models wherein the strong CP problem is solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/axino supermultiplet. We examine R-parity conserving models where the neutralino is the lightest SUSY partic
le, so that a mixture of neutralinos and axions serve as cold dark matter. The mixed axion/neutralino CDM scenario can match the measured dark matter abundance for SUSY models which typically give too low a value of the usual thermal neutralino abundance, such as models with wino-like or higgsino-like dark matter. The usual thermal neutralino abundance can be greatly enhanced by the decay of thermally-produced axinos to neutralinos, followed by neutralino re-annihilation at temperatures much lower than freeze-out. In this case, the relic density is usually neutralino dominated, and goes as sim (f_a/N)/m_{axino}^{3/2}. If axino decay occurs before neutralino freeze-out, then instead the neutralino abundance can be augmented by relic axions to match the measured abundance. Entropy production from late-time axino decays can diminish the axion abundance, but ultimately not the neutralino abundance. In mixed axion/neutralino CDM models, it may be possible to detect both a WIMP and an axion as dark matter relics. We also discuss possible modifications of our results due to production and decay of saxions. In the appendices, we present expressions for the Hubble expansion rate and the axion and neutralino relic densities in radiation, matter and decaying-particle dominated universes.
