Dirac Gauginos in Supersymmetry -- Suppressed Jets + MET Signals: A Snowmass Whitepaper

We consider the modifications to squark production in the presence of a naturally heavier Dirac gluino. First generation squark production is highly suppressed, providing an interesting but challenging signal find or rule out. No dedicated searches for supersymmetry with a Dirac gluino have been performed, however a reinterpretation of a "decoupled gluino" simplified model suggests the bounds on a common first and second generation squark mass is much smaller than in the MSSM: \lsim 850 GeV for a massless LSP, and no bound for an LSP heavier than about 300 GeV. We compare and contrast the squark production cross sections between a model with a Dirac gluino and one with a Majorana gluino, updating earlier results in the literature to a $pp$ collider operating at $\sqrt{s} = 14$ and 33 TeV. Associated production of squark+gluino is likely very small at $\sqrt{s} = 14$ TeV, while is a challenging but important signal at even higher energy $pp$ colliders. Several other salient implications of Dirac gauginos are mentioned, with some thought-provoking discussion as it regards the importance of the various experiments planned or proposed.Comment: 10 pages, 6 figures; this Snowmass Whitepaper has been submitted to arXiv at the request of the Snowmass convener

CP violation and mixing in technicolor models

Vacuum alignment in technicolor models provides an attractive origin for the quarks' CP violation and, possibly, a natural solution for the strong-CP problem of QCD. We discuss these topics in this paper. Then we apply them to determine plausible mixing matrices for left and right-handed quarks. These matrices determine the Cabibbo-Kobayashi-Maskawa matrix as well as new mixing angles and phases that are observable in extended technicolor (ETC) and topcolor (TC2) interactions. We determine the contributions of these new interactions to CP-violating and mixing observables in the K0, Bd and Bs systems. Consistency with mixing and CP violation in the K0 system requires assuming that ETC interactions are electroweak generation-conserving even if technicolor has a walking gauge coupling. Large ETC gauge boson masses and small intergenerational mixing then result in negligibly small ETC contributions to B-meson mixing and CP violation and to Re(ϵ′/ϵ). We confirm our earlier strong lower bounds on TC2 gauge boson masses from Bd–¯¯¯Bd mixing. We then pay special attention to the possibility that current experiments indicate a deviation from standard model expectations of the values of sin2β measured in Bd→J/ψKS, ϕKS, η′KS, and πKS, studying the ability of TC2 to account for these. We also determine the TC2 contribution to ΔMBs and to Re(ϵ′/ϵ), and find them to be appreciable.First author draf

Insights Into the Carboxyltransferase Reaction of Pyruvate Carboxylase From the Structures of Bound Product and Intermediate Analogs

Pyruvate carboxylase (PC) is a biotin-dependent enzyme that catalyzes the MgATP- and bicarbonate-dependent carboxylation of pyruvate to oxaloacetate, an important anaplerotic reaction in central metabolism. The carboxyltransferase (CT) domain of PC catalyzes the transfer of a carboxyl group from carboxybiotin to the accepting substrate, pyruvate. It has been hypothesized that the reactive enolpyruvate intermediate is stabilized through a bidentate interaction with the metal ion in the CT domain active site. Whereas bidentate ligands are commonly observed in enzymes catalyzing reactions proceeding through an enolpyruvate intermediate, no bidentate interaction has yet been observed in the CT domain of PC. Here, we report three X-ray crystal structures of the Rhizobium etli PC CT domain with the bound inhibitors oxalate, 3-hydroxypyruvate, and 3-bromopyruvate. Oxalate, a stereoelectronic mimic of the enolpyruvate intermediate, does not interact directly with the metal ion. Instead, oxalate is buried in a pocket formed by several positively charged amino acid residues and the metal ion. Furthermore, both 3-hydroxypyruvate and 3-bromopyruvate, analogs of the reaction product oxaloacetate, bind in an identical manner to oxalate suggesting that the substrate maintains its orientation in the active site throughout catalysis. Together, these structures indicate that the substrates, products and intermediates in the PC-catalyzed reaction are not oriented in the active site as previously assumed. The absence of a bidentate interaction with the active site metal appears to be a unique mechanistic feature among the small group of biotin-dependent enzymes that act on α-keto acid substrates

A Substrate-induced Biotin Binding Pocket in the Carboxyltransferase Domain of Pyruvate Carboxylase

Biotin-dependent enzymes catalyze carboxyl transfer reactions by efficiently coordinating multiple reactions between spatially distinct active sites. Pyruvate carboxylase (PC), a multifunctional biotin-dependent enzyme, catalyzes the bicarbonate- and MgATP-dependent carboxylation of pyruvate to oxaloacetate, an important anaplerotic reaction in mammalian tissues. To complete the overall reaction, the tethered biotin prosthetic group must first gain access to the biotin carboxylase domain and become carboxylated and then translocate to the carboxyltransferase domain, where the carboxyl group is transferred from biotin to pyruvate. Here, we report structural and kinetic evidence for the formation of a substrate-induced biotin binding pocket in the carboxyltransferase domain of PC from Rhizobium etli. Structures of the carboxyltransferase domain reveal that R. etli PC occupies a symmetrical conformation in the absence of the biotin carboxylase domain and that the carboxyltransferase domain active site is conformationally rearranged upon pyruvate binding. This conformational change is stabilized by the interaction of the conserved residues Asp590 and Tyr628 and results in the formation of the biotin binding pocket. Site-directed mutations at these residues reduce the rate of biotin-dependent reactions but have no effect on the rate of biotin-independent oxaloacetate decarboxylation. Given the conservation with carboxyltransferase domains in oxaloacetate decarboxylase and transcarboxylase, the structure-based mechanism described for PC may be applicable to the larger family of biotin-dependent enzymes

Natural Supersymmetry and Implications for Higgs physics

We re-analyze the LHC bounds on light third generation squarks in Natural Supersymmetry, where the sparticles have masses inversely proportional to their leading-log contributions to the electroweak symmetry breaking scale. Higgsinos are the lightest supersymmetric particles; top and bottom squarks are the next-to-lightest sparticles that decay into both neutral and charged Higgsinos with well-defined branching ratios determined by Yukawa couplings and kinematics. The Higgsinos are nearly degenerate in mass, once the bino and wino masses are taken to their natural (heavy) values. We consider three scenarios for the stop and sbottom masses: (I) $\tilde{t}_R$ is light, (II) $\tilde{t}_L$ and $\tilde{b}_L$ are light, and (III) $\tilde{t}_R$, $\tilde{t}_L$, and $\tilde{b}_L$ are light. Dedicated stop searches are currently sensitive to Scenarios II and III, but not Scenario I. Sbottom-motivated searches ($2 b + \rm{MET}$) impact both squark flavors due to \tilde{t} \ra b \charp_1 as well as \tilde{b} \ra b \neut_{1,2}, constraining Scenarios I and III with somewhat weaker constraints on Scenario II. The totality of these searches yield relatively strong constraints on Natural Supersymmetry. Two regions that remain are: (1) the "compressed wedge", where $(m_{\tilde{q}} - |\mu|)/m_{\tilde{q}} \ll 1$, and (2) the "kinematic limit" region, where m_{\tilde{q}} \gsim 600-750 GeV, at the kinematic limit of the LHC searches. We calculate the correlated predictions for Higgs physics, demonstrating that these regions lead to distinct predictions for the lightest Higgs couplings that are separable with \simeq 10% measurements. We show that these conclusions remain largely unchanged once the MSSM is extended to the NMSSM in order to naturally obtain a large enough mass for the lightest Higgs boson consistent with LHC data.Comment: 18 pages, 8 figure

Semileptonic decays of the Higgs boson at the Tevatron

We examine the prospects for extending the Tevatron reach for a Standard Model Higgs boson by including the semileptonic Higgs boson decays h --> WW --> l nu jj for M_h >~ 2 M_W, and h --> W jj --> l nu jj for M_h <~ 2 M_W, where j is a hadronic jet. We employ a realistic simulation of the signal and backgrounds using the Sherpa Monte Carlo event generator. We find kinematic selections that enhance the signal over the dominant W+jets background. The resulting sensitivity could be an important addition to ongoing searches, especially in the mass range 120 <~ M_h <~ 150 GeV. The techniques described can be extended to Higgs boson searches at the Large Hadron Collider.Comment: 68 pages, 19 figure