The basic structure of top-quarks as spin-1/2 particles is characterized by the radius Rt and the intrinsic magnetic dipole moment κt, both individually associated with gauge interactions. They are ...predicted to be zero in pointlike theories as the Standard Model. We derive upper limits of these parameters in the color sector from cross sections measured at Tevatron and LHC in top pair production pp¯/pp→tt¯, and we predict improved limits expected from LHC in the future, especially for analyses exploiting boosted top final states. An additional method for measuring the intrinsic parameters is based on tt¯+jet final states.
Higgs bosons can be searched for in the channels pp macro/pp-->tt macro H + X at the Fermilab Tevatron and the Cern Large Hadron Collider (LHC). We have calculated the QCD corrections to these ...processes in the standard model at next-to-leading order. The higher-order corrections reduce the renormalization and factorization scale dependence considerably and stabilize the theoretical predictions for the cross sections. At the central scale mu = (2m(t)+M(H))/2 the properly defined K factors are slightly below unity for the Tevatron (K approximately 0.8) and slightly above unity for the LHC (K approximately 1.2).
The color gauge hyper-multiplet in N=2 supersymmetry consists of the usual N=1 gauge vector/gaugino super-multiplet, joined with a novel gaugino/scalar super-multiplet. Large cross sections are ...predicted for the production of pairs of the color-octet scalars σ sgluons at the LHC: gg, qq¯→σσ*. Single σ production is possible at one-loop level, but the gg→σ amplitude vanishes in the limit of degenerate L and R squarks. When kinematically allowed, σ decays predominantly into two gluinos, whose cascade decays give rise to a burst of eight or more jets together with four LSP's as signature for σ pair events at the LHC. σ can also decay into a squark–antisquark pair at tree level. At one-loop level σ decays into gluons or a tt¯ pair are predicted, generating exciting resonance signatures in the final states. The corresponding partial widths are very roughly comparable to that for three body final states mediated by one virtual squark at tree level.
The Higgs sector is extended in R-symmetric supersymmetry theories by two iso-doublets Rd,u which complement the standard iso-doublets Hd,u. We have analyzed masses and interactions of these novel ...states and describe their non-standard decay modes and their production channels at the LHC and e+e− colliders.
Multiple Higgs-portal and gauge-kinetic mixings Choi, S. Y.; Englert, C.; Zerwas, P. M.
European physical journal. C, Particles and fields,
12/2013, Letnik:
73, Številka:
12
Journal Article
Recenzirano
Odprti dostop
We develop a phenomenological formalism for mixing effects between the Standard Model and hidden-sector fields, motivated by dark matter in the Universe as well as string theories. The scheme ...includes multiple Higgs-portal interactions in the scalar sector as well as multiple gauge-kinetic mixings in the abelian gauge sector. While some of the mixing effects can be cast in closed form, other elements can be controlled analytically only by means of perturbative expansions in the ratio of standard scales over large hidden scales. Higgs and vector-boson masses and mixings are illustrated numerically for characteristic processes.
The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics ...return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.
In the
N
= 1 supersymmetric extension of the Standard Model, neutralinos associated in supermultiplets with the neutral electroweak gauge and Higgs bosons are, as well as gluinos, Majorana fermions. ...They can be paired with the Majorana fermions of novel gaugino/scalar supermultiplets, as suggested by extended
N
= 2 supersymmetry, to Dirac particles. Matter fields are not extended beyond the standard
N
= 1 supermultiplets in
N
= 1/
N
= 2 hybrid supersymmetry to preserve the chiral character of the theory. Complementing earlier analyses in the color sector, central elements of such an electroweak scenario are analyzed in the present study. The decay properties of the Dirac fermions
and of the scalar bosons
σ
are worked out, and the single and pair production-channels of the new particles are described for proton collisions at the LHC, and electron/positron and
γγ
collisions at linear colliders. Special attention is paid to modifications of the Higgs sector, identified with an
N
= 2 hypermultiplet, by the mixing with the novel electroweak scalar sector.
The ”Snowmass Points and Slopes” (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present ...and future experiments. This set of benchmarks was agreed upon at the 2001 ”Snowmass Workshop on the Future of Particle Physics” as a consensus based on different existing proposals.
The Higgs boson spectrum of the next-to-minimal supersymmetric standard model is examined. The model includes a singlet Higgs field
S in addition to the two Higgs doublets of the minimal extension. ...‘Natural’ values of the parameters of the model are motivated by their renormalization group running and the vacuum stability. The qualitative features of the Higgs boson masses are dependent on how strongly the Peccei–Quinn
U(1) symmetry of the model is broken, measured by the self-coupling of the singlet field in the superpotential. We explore the Higgs boson masses and their couplings to gauge bosons for various representative scenarios.
PDF
