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Register a new userNatural Supersymmetry: Status and Prospects
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Xerxes Tata
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The realization that supersymmetry (SUSY), if softly broken at the weak scale, can stabilize the Higgs sector led many authors to explore the role it may play in particle physics. It was widely anticipated that superpartners would reveal themselves once the TeV scale was probed in high energy collisions. Experiments at the LHC have not yet revealed any sign for direct production of superpartners, or for any other physics beyond the Standard Model. This has led to some authors to question whether weak scale SUSY has a role to play in stabilizing the Higgs sector. We show that SUSY models with just the minimal particle content may well be consistent with data and simultaneously serve to stabilize the Higgs sector, if model parameters generally regarded as independent turn out to be appropriately correlated. In our view, it would be premature to ignore this possibility, given that we do not understand the underlying mechanism of SUSY breaking. We advocate using the electroweak scale quantity, $delew$, to determine whether a given SUSY spectrum might arise from a theory with low fine-tuning, even when the parameters correlations mentioned above are present. We find that all such models contain light higgsinos and that this leads to the possibility of new strategies for searching for SUSY. We discuss phenomenological implications of these models for SUSY searches at the LHC and its luminosity and energy upgrades, as well as at future electron-positron colliders. We conclude that natural SUSY, defined as no worse than a part in 30 fine-tuning, will not escape detection at a $pp$ collider operating at 27~TeV and an integrated luminosity of 15~ab$^{-1}$, or at an electron-positron collider with a centre-of-mass energy of 600~GeV.
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Insight into the electroweak (EW) and Higgs sectors can be achieved through measurements of vector boson scattering (VBS) processes. The scattering of EW bosons are rare processes that are precisely predicted in the Standard Model (SM) and are closely related to the Higgs mechanism. Modifications to VBS processes are also predicted in models of physics beyond the SM (BSM), for example through changes to the Higgs boson couplings to gauge bosons and the resonant production of new particles. In this review, experimental results and theoretical developments of VBS at the Large Hadron Collider, its high luminosity upgrade, and future colliders are presented.
In the context of supersymmetry, the two-loop Barr-Zee diagrams which induce CP-violating electric dipole moment of electron due to superpartners simultaneously yield CP-conserving magnetic dipole moment of muon. In this paper, we derive the coherence between the electric and magnetic dipole moments at two-loop level due to stops, charginos or neutralinos-charginos. We also use the coherence to constrain superpartner masses and their CP-violating phases, in the light of recent ACME limit on the electric dipole moment of electron and future experiments about magnetic dipole moment of muon such as Fermilab E989 experiment.
Gluinos that result in classic large missing transverse momentum signatures at the LHC have been excluded by 2011 searches if they are lighter than around 800 GeV. This adds to the tension between experiment and supersymmetric solutions of the naturalness problem, since the gluino is required to be light if the electroweak scale is to be natural. Here, we examine natural scenarios where supersymmetry is present, but was hidden from 2011 searches due to violation of R-parity and the absence of a large missing transverse momentum signature. Naturalness suggests that third generation states should dominate gluino decays and we argue that this leads to a generic signature in the form of same-sign, flavour-ambivalent leptons, without large missing transverse momentum. As a result, searches in this channel are able to cover a broad range of scenarios with some generality and one should seek gluinos that decay in this way with masses below a TeV. We encourage the LHC experiments to tailor a search for supersymmetry in this form. We consider a specific case that is good at hiding: baryon number violation, and estimate that the most constraining existing search from 2011 data implies a lower bound on the gluino mass of 550 GeV.
ANAIS (Annual modulation with NAI Scintillators) experiment aims to look for dark matter annual modulation with 250 kg of ultrapure NaI(Tl) scintillators at the Canfranc Underground Laboratory (LSC), in order to confirm the DAMA/LIBRA positive signal in a model-independent way. The detector will consist in an array of close-packed single modules, each of them coupled to two high efficiency Hamamatsu photomultipliers. Two 12.5 kg each NaI(Tl) crystals provided by Alpha Spectra are currently taking data at the LSC. These modules have shown an outstanding light collection efficiency (12-16 phe/keV), about the double of that from DAMA/LIBRA phase 1 detectors, which could enable reducing the energy threshold down to 1 keVee. ANAIS crystal radiopurity goals are fulfilled for 232Th and 238U chains, assuming equilibrium, and in the case of 40K, present crystals activity (although not at the required 20 ppb level) could be acceptable. However, a 210Pb contamination out-of-equilibrium has been identified and its origin traced back, so we expect it will be avoided in next prototypes. Finally, current status and prospects of the experiment considering several exposure and background scenarios are presented.
Maximally Natural Supersymmetry, an unusual weak-scale supersymmetric extension of the Standard Model based upon the inherently higher-dimensional mechanism of Scherk-Schwarz supersymmetry breaking (SSSB), possesses remarkably good fine tuning given present LHC limits. Here we construct a version with precision $SU(2)_{rm L} times U(1)_{rm Y} $ unification: $sin^2 theta_W(M_Z) simeq 0.231$ is predicted to $pm 2%$ by unifying $SU(2)_{rm L} times U(1)_{rm Y} $ into a 5D $SU(3)_{rm EW}$ theory at a Kaluza-Klein scale of $1/R_5 sim 4.4,{rm TeV}$, where SSSB is simultaneously realised. Full unification with $SU(3)_{rm C}$ is accommodated by extending the 5D theory to a $N=4$ supersymmetric $SU(6)$ gauge theory on a 6D rectangular orbifold at $1/R_6 sim 40 ,{rm TeV}$. TeV-scale states beyond the SM include exotic charged fermions implied by $SU(3)_{rm EW}$ with masses lighter than $sim 1.2,{rm TeV}$, and squarks in the mass range $1.4,{rm TeV} - 2.3,{rm TeV}$, providing distinct signatures and discovery opportunities for LHC run II.
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