Narrow Results

We present the results of a search for charged Higgs in the decay products of at the CDF II detector at the Tevatron. The search is based on the cross section measurements of production in three exclusive decay channels: dilepton, lepton + jets and lepton + hadronic tau. Assuming the charged Higgs decays only via , and , and , limits in the MSSM (m_Higgs, tan(β)) plane are obtained at tree level. A model-independent analysis is introduced in which the results are independent of Higgs branching ratios. This analysis results in BR(t→Hb)<0.7 at 95%CL for 80 GeV<m_Higgs<150 GeV.

We present the results of a search for a neutral MSSM Higgs boson decaying to a pair of tau leptons. The analyzed data sample corresponds to integrated luminosity of approximately 200 pb^-1 of collisions at . It was collected by the CDF detector during Run 2 of the Fermilab Tevatron. We select tau pairs in which one of the taus decays hadronically and the other to e or μ and neutrinos. We see no evidence of signal and perform a fit to the (partially) reconstructed di-tau mass to set limits on the product of Higgs production cross-section and its branching fraction to taus.

We present results for the production cross section of a Higgs boson with a pair of quarks, including next-to-leading order (NLO) QCD corrections.

The present constraints from electroweak radiative corrections suggest that the low mass region will be particularly interesting in future Higgs boson searches. In this paper, the discovery potential for a search of a low mass Standard Model Higgs boson, as well as the sensitivity to the lightest Higgs boson of the MSSM (h) are presented as a function of the collected luminosity, for the ATLAS experiment at the LHC.

Various aspects of the Higgs boson phenomenology of the Minimal Supersymmetric Standard Model (MSSM) are reviewed. Emphasis is put on the effects of higher-order corrections. The masses and couplings are discussed in the MSSM with real and complex parameters. Higher-order corrections to Higgs boson production channels at a prospective e⁺e^- linear collider are investigated. Corrections to Higgs boson decays to SM fermions and their phenomenological implications for hadron and lepton colliders are explored.

The running mass of the b-quark defined in -scheme is one of the important parameters of SUSY QCD. To find its value, it should be related to some known experimental input. In this paper, the b-quark running mass defined in nonsupersymmetric QCD is chosen for determination of the corresponding parameter in SUSY QCD. The relation between these two quantities is found by considering five-flavor QCD as an effective theory obtained from its supersymmetric extension. A numerical analysis of the calculated two-loop relation and its impact on the MSSM spectrum is discussed. Since for nonsupersymmetric models -scheme is more natural than , we also propose a new procedure that allows one to calculate relations between - and -parameters. Unphysical ε-scalars that give rise to the difference between the above-mentioned schemes are assumed to be heavy and decoupled in the same way as physical degrees of freedom. By means of this method it is possible to "catch two rabbits," i.e. decouple heavy particles and turn from to , at the same time. An explicit two-loop example of transition is given in the context of QCD. The advantages and disadvantages of the method are briefly discussed.

We write explicit and self-contained asymptotic expressions for the tensorial B, C and D Passarino–Veltman functions. These include quadratic and linear logarithmic terms, as well as subleading constant terms. Only mass-suppressed contributions are neglected. We discuss the usefulness of such expressions, particularly for studying one-loop effects in 2-to-2 body processes at high energy.

Although in the framework of the Standard Model (SM) of particles, Lepton Flavor Violating (LFV) processes such as µ → eγ, µ → eee and µN → eN are strictly forbidden, in various beyond SM scenarios such as Minimal Supersymmetric Standard Model (MSSM), new sources of LFV appear that can lead to sizeable rates for these processes. There are on-going experiments that search for the LFV processes. If the rates of these processes are close to the present bound, these experiments will collect abundant amount of data which makes precision measurement of LFV parameters a close possibility. We show that by studying the polarization of the final particles, information on the CP-violating phases of the underlying theory can be also derived. We discuss the possibility to reduce the degeneracy of parameters by combining information from various experiments.

Masses of heavy Standard Model (SM) fermions (top-quark, bottom-quark and tau-lepton) play an important role in the analysis of theories beyond the SM. They serve as low-energy input and reduce the parameter space of such theories. In this paper Minimal supersymmetric extension of the SM is considered and two-loop relations between known SM values of fermion masses and running parameters of the MSSM are studied within the effective theory approach. Both b-quark and τ-lepton have the same quantum numbers with respect to SU(2) group and in the MSSM acquire their masses due to interactions with the same Higgs doublet. As a consequence, for large values of tan β parameter corresponding Yukawa couplings also become large and together with tan β can significantly enhance radiative corrections. In the case of b-quark two-loop contribution to the relation between running bottom-quark mass in QCD and MSSM is known in literature. This paper is devoted to calculation of the NNLO corrections proportional to Yukawa couplings. For the τ-lepton obtained contribution can be considered as a good approximation to the full two-loop result. For the b-quark numerical analysis given in the paper shows that only the sum of strong and Yukawa corrections can play such a role.

We present a complete and minimal catalogue of MSSM gauge invariant monomials. That is, the catalogue of Gherghetta, Kolda and Martin is elaborated to include generational structure for all monomials. Any gauge invariant operator can be built as a linear combination of elements of the catalogue lifted to nonnegative integer powers. And the removal of any one of the monomials would deprive the catalogue of this feature. It contains 712 monomials, plus 3 generations of right-handed neutrinos if one extends the model to the νMSSM. We note that νMSSM flat directions can all be lifted by the sixth-order superpotential compared to the ninth-order needed in MSSM.

We expand the superpotential of νMSSM to sixth order. This is the order at which all flat directions can be lifted. All 5179 (complex) couplings are independent, i.e. the superpotential cannot be zero for all fields, without all couplings being zero. Likewise, any gauge invariant potential to the sixth order can be made by fixing the constants. A specific and well-defined choice of normalization has been adopted. The case for investigating this potential, rather than looking at one or several generalized flat directions is made.

The matter spectrum of the MSSM, including three right-handed neutrino supermultiplets and one pair of Higgs–Higgs conjugate superfields, can be obtained by compactifying the E₈ ×E₈ heterotic string and M-theory on Calabi–Yau manifolds with specific SU(4) vector bundles. These theories have the standard model gauge group augmented by an additional gauged U(1)_B-L. Their minimal content requires that the B-L gauge symmetry be spontaneously broken by a vacuum expectation value of at least one right-handed sneutrino. In previous papers, we presented the results of a quasianalytic renormalization group analysis showing that B-L gauge symmetry is indeed radiatively broken with an appropriate B-L/electroweak hierarchy. In this paper, we extend these results by (1) enlarging the initial parameter space and (2) explicitly calculating the renormalization group equations numerically. The regions of the initial parameter space leading to realistic vacua are presented and the B-L/electroweak hierarchy computed over these regimes. At representative points, the mass spectrum for all sparticles and Higgs fields is calculated and shown to be consistent with present experimental bounds. Some fundamental phenomenological signatures of a nonzero right-handed sneutrino expectation value are discussed, particularly the cosmology and proton lifetime arising from induced lepton and baryon number violating interactions.

We construct supersymmetric Pati–Salam flux vacua in AdS from intersecting D6-branes on T⁶/(ℤ₂ × ℤ′₂). The models constructed have three generations of MSSM matter plus right-handed neutrinos. Because the cycles wrapped by the D-branes are rigid there are no extra massless fields in the adjoint representation, arising as open-string moduli. However, we find that it is problematic to break the Pati–Salam gauge symmetry to the Standard Model (SM) while keeping the SM hypercharge massless.

We study the cross-section of heavy Higgs production at the LHC within the framework of the constrained MSSM. It is not only enhanced by tan²β but sometimes is also enhanced by the squark contribution. First, we consider the universal scenario within mSUGRA and find out that to get the desired enhancement one needs large negative values of A₀, which seems to be incompatible with the b → sγ decay rate. To improve the situation, we release the unification requirement in the Higgs sector. Then it becomes possible to satisfy all requirements simultaneously and enhance the squark contribution. The latter can gain a factor of several units increasing the overall cross-section which, however, is still smaller than the cross-section of the associated production. We consider also some other consequences of the chosen benchmark point.

Flavor violating processes in the quark and lepton sectors are investigated within a realistic supersymmetric SO(10)×A₄ grand unification model. By employing exotic heavy fermion fields, this model successfully describes various features of the fermion masses and mixings including large neutrino mixings accompanied by small quark mixings. In this model the flavor violation is induced at GUT scale, at which A₄ flavor symmetry is broken, as a consequence of the large mixings of the light fermion fields with these exotic heavy fields. The stringent experimental constraint from μ→eγ decay rate necessitates a high degree of degeneracy of the supersymmetry breaking soft scalar masses of the exotic heavy fields and supersymmetric scalar partners of the light fermion fields. The choice of slepton masses of order 1 TeV is found to be consistent with the constraints from branching ratio of μ→eγ and with all other flavor changing neutral current processes being sufficiently suppressed.

A survey of the mSUGRA/CMSSM parameter space is presented. The viable regions of the parameter space which satisfy standard experimental constraints are identified and discussed. These constraints include a 124–127 GeV mass for the lightest CP-even Higgs and the correct relic density for cold dark matter. The superpartner spectra corresponding to these regions fall within the well-known hyperbolic branch and are found to possess sub-TeV neutralinos and charginos, with mixed Bino/Higgsino LSP's with 200–800 GeV masses. In addition, the models possess ~3–4 TeV gluino masses and heavy squarks and sleptons with masses . Spectra with a Higgs mass m_h ≅125 GeV and a relic density 0.105 ≤ Ω_χ⁰ h² ≤ 0.123 are found to require EWFT at around the one-percent level, while those spectra with a much lower relic density require EWFT of only a few percent. Moreover, the spin-independent neutralino–proton direct detection cross-sections are found to be below or within the XENON100 2σ limit and should be experimentally accessible now or in the near future. Finally, it is pointed out that the supersymmetry breaking soft terms corresponding to these regions of the mSUGRA/CMSSM parameter space (m₀ ∝ m_1/2 with and A₀ = -m_1/2) may be obtained from general flux-induced soft terms in Type IIB flux compactifications with D3 branes.

While the existence of a Higgs boson with a mass near 125 GeV has been clearly established, the detailed structure of the entire Higgs sector is yet unclear. Besides the Standard Model interpretation, various possibilities for extended Higgs sectors are being considered. The minimal supersymmetric extension (MSSM) features two Higgs doublets resulting in five physical Higgs bosons, which are subject to direct searches. Alternatively, more generic Two-Higgs Doublet models (2HDM) are used for the interpretation of results. The Next-to-Minimal Supersymmetric Model (NMSSM) has a more complex Higgs sector with seven physical states. Also exotic Higgs bosons decaying to invisible final states are considered. This article summarizes recent findings based on results from collider experiments.

Recent progress is presented on higher-order calculations for the mass spectrum of Higgs particles in the CP-conserving and CP-violating MSSM, covering diagrammatic two-loop calculations for neutral and charged Higgs bosons as well as all-order resummation of large logarithms arising from the strong and Yukawa coupling sectors.

We study the rare decays D⁺→π⁺ℓ⁺ℓ^-, and D⁰→ℓ⁺ℓ^-(ℓ = e, μ) in the minimal supersymmetic standard model with and without R-parity. Using the strong constraints on relevant supersymmetric parameters from mixing and decay, we examine constrained supersymmetry contributions to relevant branching ratios, direct CP violations and ratios of and decay rates. We find that both R-parity conserving LR as well as RL mass insertions and R-parity violating squark exchange couplings have huge effects on the direct CP violations of , moreover, the constrained LR and RL mass insertions still have obvious effects on the ratios of and decay rates. The direct CP asymmetries and the ratios of and decay rates are very sensitive to both moduli and phases of relevant supersymmetric parameters. In addition, the differential direct CP asymmetries of are studied in detail.

We consider the measurement of the trilinear couplings of the neutral Higgs bosons in the minimal supersymmetric standard model (MSSM) at a high energy $e^{+}{e}^{-}$ linear collider in the light of the discovery of a Higgs boson at the CERN Large Hadron Collider (LHC). We identify the state observed at the LHC with the lightest Higgs boson $(h^0)$ of the MSSM, and impose the constraints following from this identification, as well as other experimental constraints on the MSSM parameter space. In order to measure trilinear neutral Higgs couplings, we consider different processes where the heavier Higgs boson $(H^0)$ of the MSSM is produced in electron–positron collisions, which subsequently decays into a pair of lighter Higgs boson. We identify the regions of the MSSM parameter space where it may be possible to measure the trilinear couplings of the Higgs boson at a future electron–positron collider. A measurement of the trilinear Higgs couplings is a crucial step in the construction of the Higgs potential, and hence in establishing the phenomena of spontaneous symmetry breaking in gauge theories.