N=2 (Z3-graded) paragrassmann supersymmetry with slq(2) symmetry

N=2 Z₃-graded SUSY is discussed by introducing two Z₃-graded variables which are q-commutative. The action for an N=2 Z₃-graded superfield is obtained so that it has Z₃-SUSY and sl_q(2) symmetry.     

The Higgs mass beyond the CMSSM

The recent discovery of a new boson at the LHC, which resembles a SM-like Higgs boson with m _h =125 GeV, is starting to provide strong guidelines into SUSY model building. For instance, the identification of such a state with the lightest CP-even Higgs boson of the MSSM (h ⁰), requires large values of tanβ and/or heavy sfermions. One outcome of this result is the possibility to solve the SUSY flavor and CP problems by decoupling, which points towards some realization of Split-inspired SUSY scenarios, in which scalars are much heavier than gauginos and higgsinos. However, we argue here that the remaining Higgs bosons of the MSSM (H ⁰, A ⁰, H ^±) do not have to be as heavy as the sfermions, and having them with masses near the EW scale does not pose any conflict with current MSSM constraints. We discuss then some SUSY scenarios with heavy sfermions, from a bottom-up approach, which contain the full Higgs sector, as well as a possible dark matter candidate, with masses near the EW scale, and identify distinctive signals from these scenarios that could be searched at the LHC.     

The Higgs-photon-Z boson coupling revisited

We analyze the coupling of CP-even and CP-odd Higgs bosons to a photon and a Z boson in extensions, of the Standard Model. In particular, we study in detail the effect of charged Higgs bosons in two-Higgs doublet models;. and the contribution of SUSY particle loops in the minimal supersymmetric extension of the Standard Model: The Higgs-γZ coupling can be measured in the decayZ → γ+Higgs ate ⁺ e ^? colliders running on theZ resonance, or in the reverse process Higgs →Zγ with the Higgs boson produced at LHC. We show that a measurement of this coupling with a precision at the percent level, which could be the case at futuree ⁺ e ^? colliders, would allow to distinguish between the lightest SUSY and standard Higgs bosons in large areas of the parameter space.     

Replication of lepton and quark fields and stability of the proton in N = 2 SUSY GUTs

We show that in N = 2 SUSY GUTs, leptons and quarks tend to combine with their mirror partners and to acquire very large masses proportional to the grand-unification mass. We solve this problem by means of a replication of lepton and quark fields. Grand-unification now associates light leptons and quarks with heavy ones of masses ? m_X or 2m_X. The latter carry a non-vanishing value of the central charge 〈Z〉 = ± m_X or ± 2m_X (which may be viewed as the fifth or sixth component of the covariant momentum). The exchanges of the grand-unification gauge bosons do not induce proton decay, and the proton is stable, in minimal N = 2 SUSY GUTs. Moreover the grand-unification mass does not get renormalized.     

Radiative corrections toe + e −→Zh 0 andZ→γh 0 in the minimal supersymmetric theory

The Higgs sector of the minimal supersymmetric extension of the standard model (MSSM) becomes phenomenologically hard to distinguish from the standard model (SM) in the limit that the CP-odd scalar,A ⁰, is much heavier than theZ boson. If, in addition, all the superpartners lie outside the kinematic reach of present-day (or near-future) colliders the only experimental evidence for supersymmetry (SUSY) might be through internal loops involving superpartners. We have calculated sfermion-induced radiative corrections toe ⁺ e ^?→Zh ⁰ andZ→γh ⁰ in the MSSM, which are enhanced for highm _t .     

Optical and x-ray diffraction investigations of the symmetry of distorted phases of the (NH4)2KGaF6 crystal

Powders and single-crystal plates of different sections of an (NH₄)₂KGaF₆ crystal are investigated using polarized light microscopy and x-ray diffraction over a wide temperature range, including the phase transition temperatures. It is established that the sequence of symmetry changes in the crystal under investigation is as follows: O _h ⁵ ?Fm3m (Z = 4) ? C _4h ⁵ ?I114/m (Z = 2) ? C _2h ⁵ ?P112₁/n (Z = 2).     

Constraints on the MSSM from the Higgs sector

We discuss the constraints on supersymmetry in the Higgs sector arising from LHC searches, rare B decays and dark matter direct detection experiments. We show that constraints derived on the mass of the lightest h ⁰ and the CP-odd A ⁰ bosons from these searches are covering a larger fraction of the SUSY parameter space compared to searches for strongly interacting supersymmetric particle partners. We discuss the implications of a mass determination for the lightest Higgs boson in the range 123<M _h <127?GeV, inspired by the intriguing hints reported by the ATLAS and CMS Collaborations, as well as those of a non-observation of the lightest Higgs boson for MSSM scenarios not excluded at the end of 2012 by LHC and direct dark matter searches and their implications on LHC SUSY searches.     

<Emphasis Type="Italic">Z</Emphasis><Superscript>0</Superscript>-boson decays in a strong electromagnetic field

The probability of Z ⁰-boson decay to a pair of charged fermions in a strong electromagnetic field, Z ⁰ → \(\bar f\) f, is calculated. On the basis of a method that employs exact solutions to relativistic wave equations for charged particles, an analytic expression for the partial decay width Γ(?) = Γ(Z ⁰ → \(\bar f\) f) is obtained at an arbitrary value of the parameter ? = \(eM_Z^{ - 3} \sqrt { - (F_{\mu \nu } q^\nu )^2 } \), which characterizes the external-field strength. The total Z ⁰-boson decay width in an intense electromagnetic field, Γ _Z (?), is calculated by summing these results over all known generations of charged leptons and quarks. It is found that, in the region of relatively weak fields (? < 0.06), the field-induced corrections to the standard Z ⁰-boson decay width in a vacuum do not exceed 2%. As ? increases, the total decay width Γ _Z (?) develops oscillations against the background of its gradual decrease to the absolute-minimum point. At ?_min = 0.445, the total Z ⁰-boson decay width reaches the minimum value of Γ _Z (?_min) = 2.164 GeV, which is smaller than the Z ⁰-boson decay width in a vacuum by more than 10%. In the region of superstrong fields (? > 1), Γ _Z (?) grows monotonically with increasing external-field strength. In the region ? > 5, the t-quark-production process Z ⁰ → \(\bar t\) t, which is forbidden in the absence of an external field, begins contributing significantly to the total decay width of the Z ⁰ boson.     

Optical and x-ray diffraction studies of the symmetry of distorted phases of the (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>ZrF<Subscript>7</Subscript> crystal

(NH₄)₃ZrF₇ single crystals were grown, and polarization-optical and x-ray diffraction studies were performed on powders and crystalline plates of various cuts over a wide temperature range. Phase transitions are revealed at temperatures T _1↑ = 280 K, T _2↑ = 279.6 K, T _3↑ = 260–265 K, and T _4↑ = 238 K on heating and at T _1↓ = 280 K, T _2↓ = 269–270 K, T _3↓ = 246 K, and T _4↓ = 235 K on cooling. The sequence of changes in symmetry is established to be as follows: O _h ⁵ (Z = 4) ? D _2h ²⁵ (Z = 2) ? C _2h ³ (Z = 2) ? C _i ¹ (Z = 108) ? monoclinic²(Z = 216).     

Yukawa coupling structure in intersecting D-brane models

The structure of Yukawa coupling matrices is investigated in type IIA T ⁶/(Z₂ x Z₂) orientifold models with intersecting D-branes. Yukawa coupling matrices are difficult to be made realistic in conventional models in which the generation structure emerges by the multiple intersection of D-branes in the factorized T ⁶ = T ² x T ² x T ². We study the new type of flavor structure, where Yukawa couplings are dynamically generated, and show this type of models lead to non-trivial structures of Yukawa coupling matrices, which can be realistic.Received: 8 December 2004, Revised: 22 December 2004, Published online: 9 March 2005     

Anomalously interacting new extra vector bosons and their first LHC constraints

In this review phenomenological consequences of the Standard Model extension by means of new spin-1 chiral fields with the internal quantum numbers of the electroweak Higgs doublets are summarized. The prospects for resonance production and detection of the chiral vector Z* and W*^± bosons at the LHC energies are considered on the basis of quantitative simulations within the CompHEP/CalcHEP package. The Z* boson can be observed as a Breit-Wigner resonance peak in the invariant dilepton mass distributions in the same way as the well-known extra gauge Z?? bosons. However, the Z* bosons have unique signatures in transverse momentum, angular and pseudorapidity distributions of the final leptons, which allow one to distinguish them from other heavy neutral resonances. In 2010, with 40 pb^?1 of the LHC proton-proton data at the energy 7 TeV, the ATLAS detector was used to search for narrow resonances in the invariant mass spectrum of e ⁺ e ^? and ??⁺??^? final states and high-mass charged states decaying to a charged lepton and a neutrino. No statistically significant excess above the Standard Model expectation was observed. The exclusion mass limits of 1.15 and 1.35 TeV/c ² were obtained for the chiral neutral Z* and charged W* bosons, respectively. These are the first direct limits on the W* and Z* boson production. Based on the above, a novel strategy for the chiral boson search in the LHC dijet data is discussed. For almost all currently considered exotic models the relevant signal is expected in the central dijet rapidity region y _1,2 ? 0 and |y ₁ ? y ₂| ? 0. On the contrary, the chiral bosons do not contribute to this region but produce an excess of dijet events far away from it. In particular, for these bosons the appropriate kinematical restrictions lead to a dip in the centrality ratio distribution over the dijet invariant mass instead of a bump expected in the most exotic models.     

The new look pMSSM with neutralino and gravitino LSPs

The pMSSM provides a broad perspective on SUSY phenomenology. In this paper we generate two new, very large, sets of pMSSM models with sparticle masses extending up to 4?TeV, where the lightest supersymmetric particle (LSP) is either a neutralino or gravitino. The existence of a gravitino LSP necessitates a detailed study of its cosmological effects and we find that Big Bang Nucleosynthesis places strong constraints on this scenario. Both sets are subjected to a global set of theoretical, observational and experimental constraints resulting in a sample of ??225k viable models for each LSP type. The characteristics of these two model sets are briefly compared. We confront the neutralino LSP model set with searches for SUSY at the 7?TeV LHC using both the missing (MET) and non-missing E _T ATLAS analyses. In the MET case, we employ Monte Carlo estimates of the ratios of the SM backgrounds at?7 and?8?TeV to rescale the 7?TeV data-driven ATLAS backgrounds to 8?TeV. This allows us to determine the pMSSM parameter space coverage for this collision energy. We find that an integrated luminosity of ??5?C20?fb^?1 at 8?TeV would yield a substantial increase in this coverage compared to that at 7?TeV and can probe roughly half of the model set. If the pMSSM is not discovered during the 8?TeV run, then our model set will be essentially void of gluinos and lightest first and second generation squarks that are ?700?C800?GeV, which is much less than the analogous mSUGRA bound. Finally, we demonstrate that non-MET SUSY searches continue to play an important role in exploring the pMSSM parameter space. These two pMSSM model sets can be used as the basis for investigations for years to come.     

Can “Two-” and “One-Dimensional” Multielectron Atoms Exist?

The quasi-classical Thomas–Fermi method is applied to 2D and 1D multielectron atoms. In terms of this method, such atoms are shown not to exist because of the fact that the physical boundary conditions that are analogous to the 3D version of the theory, where boundary conditions are met, cannot be fulfilled. Our theoretical results can be experimentally tested. Atomic number Z_{1, 2max} (~10²?) is assumed to exist in terms of this method. At Z > Z_{1, 2max}, low-dimensional multielectron atoms cannot exist, in contrast to oneor two-electron atoms and, e.g., an experimentally detected Bose condensate of low-dimensional atoms with Z ~ 10 (Na).     

Electroweak corrections to monojet production at the Tevatron and the LHC

The first LHC results seem to disfavor, from the point of view of naturalness, any constrained MSSM realization with universal conditions at the SUSY-breaking scale. A more motivated scenario is given by split-family SUSY, in which the first two generations of squarks are heavy, compatible with a U(2)³ flavor symmetry. We consider this flavor symmetry to be broken at a very high scale and study the consequences at low energies through its RGE evolution. Initial conditions compatible with a split scenario are found, and the preservation of correlations from minimal U(2)³ breaking are checked. The various chiral operators in ΔF=2 processes are analyzed, and we show that, due to LHC gluino bounds, the (LL)(RR) operators cannot always be neglected. Finally, we also study a possible extension of the U(2)³ model compatible with the lepton sector.     

Hadronic contributions to (g−2) of the leptons and to the effective fine structure constant α(M Z 2 )

The new experiment planned at Brookhaven to measure the anomalous magnetic moment of the muona _μ≡(g _μ?2)/2 will improve the present accuracy of 7 ppm by about a factor of 20. This requires a careful reconsideration of the theoretical uncertainties of theg?2 predictions, which are dominated by the error of the contribution from the light quarks to the photon vacuum polarization. This issue is cruicial also for the precise determination of the running fine structure constant at theZ-peak as LEP/SLC experiments continue to increase their precision. In this paper we present an updated analysis of the hadronic vacuum polarization using all presently availablee ⁺e^? data. This seems to be justified because previous work on the subject was based to some extent on preliminary or incomplete experimental data. Contributions from different energy ranges are presented separately forg?2 of the muon and the τ-lepton and for α(M _Z ² ). We obtain the resultsa _μ ^had* =(725±16)×10^?10 anda _τ ^had* =(351±10)×10^?8, where the asterisk indicates the dressed (renormalization group improved) value. For the effective fine structure constant atM _Z=91.1888 GeV we obtainΔα _had ⁽⁵⁾ =0.0280±0.0007 and α(M _Z ² )^?1=128.896±0.090. Further improvement in the accuracy of theoretical predictions which depend on the hadronic vacuum polarization requires more precise measurements ofe ⁺e^? cross-sections at energies below about 12 GeV in future experiments.     

Dark matter in Susy models

Direct detection experiments for neutralino dark matter in the Milky Way are examined within the framework of SUGRA models with R-parity invariance and grand unification at the GUT scale, M _G. Models of this type apply to a large number of phenomena, and all existing bounds on the SUSY parameter space due to current experimental constraints are included. For models with universal soft breaking at M _G (mSUGRA), the Higgs mass and b → sγ constraints imply that the gaugino mass, m _1/2, obeys m _1/2>300–400 GeV, putting most of the parameter space in the coannihilation domain, where there is a relatively narrow band in the m ₀-m _1/2 plane. For μ>0, we find that the neutralino-proton cross section is ?10^?10 pb for m _1/2<1 TeV, making almost all of this parameter space accessible to future planned detectors. For μ<0, however, there will be large regions of parameter space with cross sections <10^?12 pb and, hence, unaccessible experimentally. If, however, the muon magnetic moment anomaly is confirmed, then μ>0 and m _1/2?800 GeV. Models with nonuniversal soft breaking in the third generation and Higgs sector can allow for new effects arising from additional early Universe annihilation through the Z-channel pole. Here, cross sections that will be accessible in the near future to the next generation of detectors can arise, and can even rise to the large values implied by the DAMA data. Thus, dark matter detectors have the possibility of studying the post-GUT physics that control the patterns of soft breaking.     

Polarized bhabha scattering in multiboson electroweak gauge models

The general expression for the differential cross section of the reactione ⁺ e ^?→γ,Z ₁ ⁰ ,Z ₂ ⁰ , ..., →e ⁺ e ^? with an arbitrary initial polarization state is derived in the context of electroweak gauge models with more than one neutral boson. Angular distributions, azimuthal asymmetries in the case of natural polarization, and longitudinal polarization asymmetries for models of the typeSU(2)×U(1)×G (G=?(1),S?(2)) and left-right symmetric models are compared with the standard model results. For the angular distributions withe ^± having equal helicities a～10% deviation from the standard model is predicted already below 50 GeV for models of the first type withZ ₁ ⁰ masses up to 80 GeV. At energies around the firstZ ₁ ⁰ a study of azimuthal and polarization asymmetries yields the possibility of distinguishing between different models.     

Threshold effects in SUSY and non-SUSY GUTs

We discuss recent contributions on threshold effects in grand unfiied theories including minimal SUSY SU (5), non-SUSY modifications of the grand desert in SU(5) and SO(10), and SO(10) with single intermediate symmetires. Consequences of theorems on vanishing GUT-scale corrections to sin² θ_w in SO(10) with SU(2) _L XSU(2) _R XSU(4) _c (g_2l =g_2R ) intermediate symmetry are discussed and vanishing corrections on the inter-mediate scale are explicitly demonstrated where predictions are more precise. Threshold and higher dimensional operator effects in SUSY SU(5) recently derived by a number of authors are presented.     

Hierarchy of quark masses in the isotopic doublets in N=1 supergravity models

In the framework of some generic softly broken SUSY models we study the SU (2) × U(1) breaking by radiative corrections, starting with the Yukawa couplings which at the Planck scale M_P satisfy h^t = h^b. Physically acceptable solutions exist with the heirarchy of VEVs: ν₂/ν₁ ≈ m_t/m_b provided m_t ⩾ 50 GeV. When the SUSY breaking is driven only by the gaugino mass the solutions uniquely predict ν₂=O(10)ν₁ and the top mass in the range 50–65 GeV. Also, the mass ratio in the second quark generation can be accounted for.     

An improved measurement of R b using a double tagging method

This paper describes an update of the double tagging measurement of the fraction, R _b, of Z⁰ → bb? events in hadronic Z⁰ decays, with statistics improved by including the data collected in 1994. The presence of electrons or muons from semileptonic decays of bottom hadrons and the detection of bottom hadron decay vertices were used together to obtain an event sample enriched in Z⁰ → bb? decays. The efficiency of the bb? event tagging was obtained from the data by comparing the numbers of events having a bottom signature in either one or both thrust hemispheres. Efficiency correlations between opposite event hemispheres are small (< 0.5%) and well understood through comparisons between the real and simulated data samples. A value of R _b = 0.2175 ± 0.0014 ± 0.0017 was obtained, where the first error is statistical and the second systematic. The uncertainty on the decay width Γ(Z⁰ → cc?) is not included in these errors. The result depends on R _c as follows: $${? Delta R_{? b}?er R_{? b}}=-0.084{? Delta R_{? c}?er R_{? c}},$$ where ΔR _c is the deviation of R _c from the value 0.172 predicted by the Standard Model.