Photon structure function in supersymmetric QCD revisited

We investigate the virtual photon structure function in the supersymmetric QCD (SQCD), where we have squarks and gluinos in addition to the quarks and gluons. Taking into account the heavy particle mass effects to the leading order in QCD and SQCD we evaluate the photon structure function and numerically study its behavior for the QCD and SQCD cases.     

Supersymmetric three-jets in electron-positron annihilation

The bremsstrahlung of gluons and gluinos off quarks and squarks is studied in e⁺e^? annihilation for longitudinally polarized beams. The contribution of a given supersymmetric state is found to be 11–27% of the conventional gluon bremsstrahlung. With all supersymmetric channels open this adds up to 90–100% of the q$\text{q}$g contribution. Dalitz-plot and angular distributions are investigated. A pronounced forward-backward asymmetry is found for gluino bremsstrahlung. Characteristic features are also exhibited by the angular distribution of the normal to the event plane.     

Massive gluinos

We show how the fermionic partners of the gluons under supersymmetry (gluinos), although massless at the classical level, can acquire masses through quantum effects. This is important for the phenomenological consequences of supersymmetric theories.     

Heavy-flavor tagging and the supersymmetry reach of the CERN Large Hadron Collider

The branching fraction for the decays of gluinos to third generation quarks is expected to be enhanced in classes of supersymmetric models where either third generation squarks are lighter than other squarks, or in mixed-higgsino dark matter models constructed so as to be in concordance with the measured density of cold dark matter. In such scenarios, gluino production events at the CERN Large Hadron Collider should be rich in top and bottom quark jets. Requiring b jets in addition to E _T ^miss should, therefore, enhance the supersymmetry signal relative to Standard Model backgrounds from V + jet, VV and QCD backgrounds (V=W,Z). We quantify the increase in the supersymmetry reach of the LHC from b-tagging in a variety of well-motivated models of supersymmetry. We also explore “top tagging” at the LHC. We find that while the efficiency for this turns out to be too low to give an increase in reach beyond that obtained via b-tagging, top tagging can indeed provide a confirmatory signal if gluinos are not too heavy. We also examine c jet tagging but find that it is not useful at the LHC. Finally, we explore the prospects for detecting the direct production of third generation squarks in models with an inverted squark mass hierarchy. This is signaled by b jets + E _T ^miss events being harder than in the Standard Model, but softer than those from the production of gluinos and heavier squarks. We find that while these events can be readily separated from the SM background (for third generation squark masses ∼300–500 GeV), the contamination from the much heavier gluinos and squarks remains formidable if these are also accessible.     

Spin structure of hadrons in supersymmetric quantum chromodynamics at short distances

We study the short-distance spin structure of nucleons in supersymmetric QCD. We calculate the Altarelli-Parisi spin transition coefficients ΔP _ba and corresponding anomalous Δ γ _ab ⁿ fora, b=quarks, gluons, gluinos and squarks and present the supersymmetric relations between them. Further analysis is divided into two parts: the parity conserving case and parity violating case, both following from the mass mixing in the squark sector. Solving theQ ²-evolution equations we determine the quark, gluon, gluino and squark spin distribution at variousQ ² above the threshold for production of supersymmetric partners. We also show the analytic solutions for the first moments in the nonsinglet and singlet sector. In particular the spin carried by the valence quarks turn out to vanish asymptotically except of one particular case of squark mixing.     

SUSY QCD Residual Effects in pp→bbh Process

If all the supersymmetry particles (sparticles) except a light Higgs boson are too heavy to be directly produced at the Large Hadron Collider (LHC), a possible way to reveal evidence for supersymmetry is through their virtual effects in other processes. We examine such supersymmetric QCD effects in bottom pair production associated with a light Higgs boson at the LHC. We find that if the relevant sparticles (gluinos and squarks) are too heavy to be directly produced well above the TeV scale, they can still have sizable virtual effects in this process. For large tanβ, such residual effects can alter the production rate by over 40 percent,which should be observable in future measurements of this process at the LHC.     

Mesino-antimesino oscillations

The phenomenology of supersymmetric theories with low scale supersymmetry breaking and a squark as the lightest standard model superpartner are investigated. Such squarks hadronize with light quarks, forming sbaryons and mesinos before decaying. Production of these supersymmetric bound states at a high energy collider can lead to displaced jets with large negative impact parameters. Neutral mesino-antimesino oscillations are not forbidden by any symmetry and can occur at observable rates. Stop mesino-antimesino oscillations would give a sensitive probe of up-type sflavor violation, and can provide a discovery channel for supersymmetry through events with a same-sign top-top topology.     

Supersymmetric enhancement factor for the 1-jet cross-section inp - \bar p reactions

We compare the 1-jet inclusive cross-section at highp _⊥ in proton-antiproton reaction atSPS collider predicted by standard QCD and by its simplest supersymmetric extension (SQCD). We first compute the total enhancement factorK between QCD and SQCD jets as a function ofp _⊥. Then we compute the observable enhancement factor which is smaller thanK since the transverse momentum of supersymmetric particles is not fully observable. We have analyzed two cases (i)p _⊥ is small compared to the masses of squarks and only light gluinos (2 GeV) are considered (ii)p _⊥ is large compared to the masses of squarks (17 GeV in our analysis) and both gluinos and squarks are taken into account. The observable enhancement factor between QCD and SQCD is found to be small (of order 1.3 to 1.5 forp _⊥=100 GeV). Missingp _⊥ events with one ordinary jet and one jet due to the production of a supersymmetric particle are found to be non negligible with respect to those with two supersymmetric jets. We also display some interesting supersymmetric relations among parton cross-sections.     

Transverse mass for pairs of gluinos

We introduce a new observable, "gluino m_{T2}," which is an application of the Cambridge m_{T2} variable to the process where gluinos are pair produced in a proton-proton collision and each gluino subsequently decays into two quarks and one lightest supersymmetric particle, i.e., g[over ]g[over ]-->qqchi[over ]_{1};{0}qqchi[over ]_{1};{0}. We show that the gluino m_{T2} can be utilized to measure the gluino mass and the lightest neutralino mass separately and also the 1st and 2nd generation squark masses if squarks are lighter than the gluino, thereby providing a good first look at the pattern of sparticle masses experimentally.     

Phenomenological implications of <Emphasis Type="Italic">D</Emphasis>3/<Emphasis Type="Italic">D</Emphasis>7 (reversed) <Emphasis Type="Italic">μ</Emphasis>-split-like supersymmetry scenario

A phenomenological model is presented which can be obtained as a local Swiss-Cheese Calabi–Yau string-theoretic compactification with a mobile D3- and fluxed stacks of wrapped D7-branes. It provides a natural realization of (reversed) μ-split-like supersymmetry wherein the squarks, sleptons, gauginos, higgsino and one of the Higgs doublets are very heavy while with some fine tuning, it is possible to obtain another light Higgs of mass 125 GeV. We discuss the role of the heavy quarks /sleptons and the light Higgs in (i) obtaining long-lived gluinos (a natural consequence of split SUSY), (ii) verifying that the NLSP decays to the gravitino LSP respects the BBN constraints with the lifetime of the LSP (gravitino) coming out to be of the order or larger than the age of the Universe, (iii) getting gravitino relic abundance of around 0.1 and (iv) obtaining electronic EDM close to the experimental upper bounds.     

LHC (CMS) discovery potential for models with effective supersymmetry and nonuniversal gaugino masses

We investigate squark and gluino pair production at LHC (CMS) with subsequent decays into quarks, leptons, and the lightest supersymmetric particles (LSP) in models with effective supersymmetry, where the third generation of squarks is relatively light, whilst the first two generations of squarks are heavy. We consider the general case of nonuniversal gaugino masses. The visibility of a signal through an excess over Standard Model background in (n≥2) jets+(m≥0) leptons+E _T ^miss events depends rather strongly on the relation between the LSP, second-neutralino, gluino, and squark masses and decreases with increasing LSP mass. We find that, for a relatively heavy gluino, it is very difficult to detect a SUSY signal even for light third-generation squarks $(m_{\tilde q_3 } \leqslant 1TeV)$ if the LSP mass is close to the third-generation squark mass.     

The SUSY-QCD <Emphasis Type="Italic">β</Emphasis> function to three loops

A number of [` DR]\overline {\mbox {\textsc{D}R}} renormalization constants in softly broken SUSY- QCD are evaluated to three-loop level: the wave function renormalization constants for quarks, squarks, gluons, gluinos, ghosts, and ε-scalars, and the renormalization constants for the quark and gluino mass as well as for all cubic vertices. The latter allow us to derive the corresponding β functions through three loops, all of which we find to be identical to the expression for the gauge β function obtained by Jack et al. (Phys. Lett. B 386:138, 1996, ) (see also Pickering et al. in Phys. Lett. B 510, 347, 2001, ). This explicitly demonstrates the consistency of DRED with SUSY and gauge invariance, an important pre-requisite for precision calculations in supersymmetric theories.     

Gluino production in electron-positron annihilation

We discuss the pair production of gluinos in electron-positron annihilation at LEP, in a model with soft supersymmetry breaking, allowing for mixing between the squarks. In much of the parameter space of the Minimal Supersymmetric Model (MSSM) the cross section corresponds to aZ branching ratio above 10^–5, even up to 10^–4. A non-observation of gluinos at this level restricts the allowed MSSM parameter space. In particular, it leads to lower bounds on the soft mass parameters in the squark sector.     

Two-jet distributions and energy-energy correlation for spin-zero quarks ine + e − annihilation

We calculate and compare with QCD the fraction of two-jet events, the two-jet angular distribution, the full energy-energy correlation and the asymmetry cross section for spinless quarks, related or not to supersymmetry. Surprisingly enough, all angle-integrated quantities look more or less the same for quarks and squarks. Only the angular distributions are sufficiently sensitive to the spin of the quark.     

Squark and gluino production at the pp collider

We present detailed calculations of the missing energy and jet signatures for squark and gluino pair-production at the CERN $\text{p}\text{p}$ collider, incorporating three improvements over previous analyses. These include smearing in transverse momentum at production, the fragmentation of supersymmetric partons into supersymmetric hadrons, and the hadronization of their decay products as well as of the residual jets. We find that previous estimates of supersymmetric signatures are not substantially altered by the inclusion of smearing and fragmentation. We present rapidity and transverse momentum distributions for both primary and secondary jets, and discuss variations in the trigger conditions which could increase the number of two-jet events and help discriminate between different models for the monojet events. We find that gluinos give fatter jets than do squarks of the same mass, although it is not easy to understand the thinness of the observed monojets if they are due to squarks of mass O(40) GeV. We emphasize that the key feature to clarify the supersymmetric interpretation of missing p_T events is the study of secondary jet production in mono- and dijet events.     

Levi-Civita connections for a class of spectral triples

Letters in Mathematical Physics - We give a new definition of Levi-Civita connection for a noncommutative pseudo-Riemannian metric on a noncommutative manifold given by a spectral triple. We prove...     

Upper bounds on supersymmetric particle masses

Based on the “naturalness” criterion, upper bounds on all superparticle masses as functions of the top quark mass are derived. These bounds give an objective criterion to test (or disprove) the idea of low-energy supersymmetry, as implemented in supergravity models. These bounds strongly differentiate weakly interacting superparticles, like charginos or neutralinos, lighter than 100–200 GeV, from strongly interacting ones, like gluinos or squarks which can become heavier than 1 TeV.     

Supersymmetry and the cohomology of (hyper) Kähler manifolds

The cohomology of a compact Kahler (hyperKähler) manifold admits the action of the Lie algebra so(2,1) (so(4,1)). In this paper we show, following an idea of Witten, how this action follows from supersymmetry, in particular from the symmetries of certain supersymmetric sigma models. In addition, many of the fundamental identities in Hodge-Lefschetz theory are also naturally derived from supersymmetry.     

Squark pair production mechanisms in pp collisions

Through a phenomenological analysis in the transverse plane of a $\text{p}\text{p}$ collision, we study different production mechanisms of squark pairs, decaying into a quark and a photino (missing energy): excitation of squarks inside the proton, fusion of light partons into squark pairs, and decay of heavier gluinos into squarks. The rates for missing transverse momentum are calculated and confronted with the monojet events observed at the CERN collider. In the framework of “minimal” supergravity models the excitation and fusion of squark pairs are disfavoured, whereas the dominant processes involve heavier gluinos and squarks cascading into photinos through intermediate squarks. The agreement with experimental data is better if heavier squarks and gluinos decay through an intermediate b-squark. We remark that energy dissipating effects during the cascade towards the final state tend to improve the comparison between theory and experiment.     

Low-energy supersymmetry and the Tevatron bottom-quark cross section

A long-standing discrepancy between the bottom-quark production cross section and predictions of perturbative quantum chromodynamics is addressed. We show that pair production of light gluinos, of mass 12 to 16 GeV, with two-body decays into bottom quarks and light bottom squarks, yields a bottom-quark production rate in agreement with hadron collider data. We examine constraints on this scenario from low-energy data and make predictions that may be tested at the next run of the Fermilab Tevatron collider.