arXiv subjects
Publications and source records attributed to A. Dedes.
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.
We investigate the Higgs boson sector of the Minimal Supersymmetric Standard Model (MSSM) in the framework of the three most prominent soft SUSY-breaking scenarios, mSUGRA, MGMSB and mAMSB. For each scenario, we determine the parameters at the electroweak scale from the set of input variables at higher energy scales (depending on the specific scenario) and evaluate the Higgs boson properties. The latter are based on results obtained within the Feynman-diagrammatic approach by taking into account the complete one-loop and the dominant two-loop contributions. The maximum value of the mass of the lightest neutral CP-even MSSM Higgs boson, m_h, is determined in the three scenarios, and the behavior of the Higgs couplings to fermions and gauge bosons is investigated. Restrictions on tan beta and on the set of higher-energy scale parameters are derived from the lower limits arising from the Higgs search at LEP2. We furthermore discuss the regions of parameter space in the three scenarios compatible with interpreting the excess observed at LEP2 as a Higgs signal, with m_h = (115.0 + 1.3 - 0.9) GeV. The case where the events observed at LEP2 could originate from the production of the heavier neutral CP-even Higgs boson is also considered. The implications of a possible Higgs signal at 115 GeV for SUSY searches at future colliders are briefly discussed for each of the three scenarios.
We analyse the rare decay mode B_s -> mu^+ mu^- in the minimal supergravity scenario (mSUGRA). We find a strong correlation with the muon anomalous magnetic moment (g-2)_mu. An interpretation of the recently measured excess in (g-2)_mu in terms of mSUGRA corrections implies a substantial supersymmetric enhancement of the branching ratio Br(B_s -> mu^+ mu^-): if (g-2)_mu exceeds the Standard Model prediction by 4*10^{-9}, Br(B_s -> mu^+ mu^-) is larger by a factor of 10-100 than in the Standard Model and within reach of Run-II of the Tevatron. Thus an experimental search for B_s -> mu^+ mu^- is a stringent test of the mSUGRA GUT scale boundary conditions. If the decay B_s -> mu^+ mu^- is observed at Run-II of the Tevatron, then we predict the mass of the lightest supersymmetric Higgs boson to be less than 120 GeV. The decay B_s -> mu^+ mu^- can also significantly probe the favoured parameter range in SO(10) SUSY GUT models.
The Higgs boson sector of the Minimal Supersymmetric Standard Model (MSSM) is investigated in a uniform way in the framework of the three most prominent soft SUSY-breaking scenarios, mSUGRA, mGMSB and mAMSB, especially concerning the Higgs searches at LEP2.
A light CP-even Higgs boson with a mass of around 10 GeV could explain the recent BNL measurement of the muon anomalous magnetic moment. This observation is based on a general CP-conserving two Higgs doublet extension of the Standard Model with no tree-level flavor changing neutral current couplings. The Higgs mass is constrained by experiments at CESR and LEP to be less than twice the lightest B-meson mass and greater than (roughly) the Upsilon mass. It may be possible to exclude or discover such a Higgs boson by fully analyzing the existing LEP data.
We study the phenomenology of a new Minimally-extended Supersymmetric Standard Model (nMSSM) where a gauge singlet superfield is added to the MSSM spectrum. The superpotential of this model contains no dimensionful parameters, thus solving the mu-problem of the MSSM. A global discrete R-symmetry, forbidding the cubic singlet self-interaction, imposed on the complete theory, guarantees its stability with respect to generated higher-order tadpoles of the singlet and solves both the domain wall and Peccei-Quinn axion problems. We give the free parameters of the model and display some general constraints on them. A particular attention is devoted to the neutralino sector where a (quasi-pure) singlino appears to be always the LSP of the model, leading to additional cascades, involving the NLSP -> LSP transition, compared with the MSSM. We then present the upper bounds on the masses of the lightest and next-to-lightest -- when the lightest is an invisible singlet -- CP-even Higgs bosons, including the full one-loop and dominant two-loop corrections. These bounds are found to be much higher than the equivalent ones in the MSSM. Finally, we discuss some phenomenological implications for the Higgs sector of the nMSSM in Higgs production at future hadron colliders.
We study the compatibility of a light bottom squark M_{\tilde b}< O(10 GeV) in the unconstrained MSSM. We consider the one-loop radiative corrections which are large for a heavy gluino (> O(150 GeV)). We then consider the renormalization group flow up to the Grand Unified scale. For most regions of the parameter space with a light sbottom we find colour and charge breaking minima. Only a small window in gluino mass and tan(beta) is consistent with all bounds. This is alleviated by a light gluino, which is however only marginally experimentally allowed.
We propose a new scenario that solves the slepton negative mass squared problem of the minimal supersymmetric standard model with anomaly mediated supersymmetry breaking. The solution is achieved by including three trilinear R-parity violating operators in the superpotential. The soft supersymmetry breaking terms satisfy renormalisation group invariant relations in terms of supersymmetric couplings and the overall supersymmetry breaking mass scale. Flavour changing neutral currents can be naturally highly suppressed. A specific model predicts tan beta=4.2+/-1.0. Excluding sleptons, the supersymmetric particle spectrum then depends upon two remaining free parameters. In the case of the R-parity violating couplings set at their quasi-fixed points at a supersymmetric GUT scale, the whole sparticle spectrum approximately depends upon only one free parameter. Imposing experimental limits leads to a constrained and distinctive phenomenology. The lightest CP-even Higgs of mass m_h=118 GeV would be seen at the Tevatron. All sparticles and heavy Higgs would evade detection except for the lightest charginos and neutralinos, whose distinctive leptonic decays would be seen at the LHC.
We consider the embedding of the Standard Model fields in a $(4+d)$-dimensional theory while gravitons may propagate in $d'$ extra, compact dimensions. We study the modification of strengths of the gravitational and gauge interactions and, for various values of $d$ and $d'$, we determine the energy scale at which these strengths are unified. Special cases where the unification of strengths is characterized by the absence of any hierarchy problem are also presented.
We present an outlook for possible discovery of supersymmetry with broken R-parity at Run II of the Tevatron. We first present a review of the literature and an update of the experimental bounds. In turn we then discuss the following processes: 1. Resonant slepton production followed by R-parity violating decay, (a) via $LQD^c$ and (b) via $LLE^c$. 2. How to distinguish resonant slepton production from $Z'$ or $W'$ production. 3. Resonant slepton production followed by the decay to neutralino LSP, which decays via $LQD^c$. 4. Resonant stop production followed by the decay to a chargino, which cascades to the neutralino LSP. 5. Gluino pair production followed by the cascade decay to charm squarks which decay directly via $L_1Q_2D^c_1$. 6. Squark pair production followed by the cascade decay to the neutralino LSP which decays via $L_1Q_2D^c_1$. 7. MSSM pair production followed by the cascade decay to the LSP which decays (a) via $LLE^c$, (b) via $LQD^c$, and (c) via $U^cD^cD^c$, respectively. 8. Top quark and top squark decays in spontaneous R-parity violation.
The Beyond the Standard Model Working Group discussed a variety of topics relating to exotic searches at current and future colliders, and the phenomenology of current models beyond the Standard Model. For example, various supersymmetric (SUSY) and extra dimensions search possibilities and constraints are presented. Fine-tuning implications of SUSY searches are derived. The implications of Higgs (non)-discovery are discussed, as well as the program HDECAY. The individual contributions are included seperately. Much of the enclosed work is original, although some is reviewed.
If the soft Supersymmetry (SUSY) breaking masses and couplings are complex, then the associated CP-violating phases can in principle modify the known phenomenological pattern of the Minimal Supersymmetric Standard Model (MSSM). We investigate here their effects on Higgs boson production in the gluon-gluon fusion mode at the Tevatron and the Large Hadron Collider (LHC), by taking into account all experimental bounds available at present. The by far most stringent ones are those derived from the measurements of the Electric Dipole Moments (EDMs) of fermions. However, it has recently been suggested that, over a sizable portion of the MSSM parameter space, cancellations among the SUSY contributions to the EDMs can take place, so that the CP-violating phases can evade those limits. We find a strong dependence of the production rates of any neutral Higgs state upon the complex masses and couplings over such parts of the MSSM parameter space. We show these effects relatively to the ordinary MSSM rates as well as illustrate them at absolute cross section level at both colliders
We show that in the MSSM without R-parity symmetry there are no new contributions to electron and neutron electric dipole moments (EDMs) at 1-loop induced by the R-parity violating Yukawa couplings. Non-zero EDMs for the electron and neutron first arise at the 2-loop level. As an example we estimate the contribution of a two-loop graph which induces electron EDMs. On the other hand, we show that the (Majorana) neutrino electric and magnetic transition moments are non-zero even at the 1-loop level. Constraints on the R-parity violating couplings are derived from the existing bounds on the neutrino dipole moments.
Assuming that the axion mechanism of solving the strong CP problem does not exist and the vanishing of theta at tree level is achieved by some model-building means, we study the naturalness of having large CP-violating sources in the leptonic sector. We consider the radiative mechanisms which transfer a possibly large CP-violating phase in the leptonic sector to the theta parameter. It is found that large theta cannot be induced in the models with one Higgs doublet as at least three loops are required in this case. In the models with two or more Higgs doublets the dominant source of theta is the phases in the scalar potential, induced by CP violation in leptonic sector. Thus, in the MSSM framework the imaginary part of the trilinear soft-breaking parameter A_l generates the corrections to the theta angle already at one loop. These corrections are large, excluding the possibility of large phases, unless the universality in the slepton sector is strongly violated.
The upper limit on the lightest CP-even Higgs boson mass, mh, is analyzed within the MSSM as a function of tan(beta) for fixed mtop and Msusy. The impact of recent diagrammatic two-loop results on this limit is investigated. We compare the MSSM theoretical upper bound on mh with the lower bound obtained from experimental searches at LEP. We estimate that with the LEP data taken until the end of 1999, the region mh < 108.2 GeV can be excluded at the 95% confidence level. This corresponds to an excluded region 0.6 <= tan(beta) <= 1.9 within the MSSM for mtop = 174.3 GeV and Msusy <= 1 TeV. The final exclusion sensitivity after the end of LEP, in the year 2000, is also briefly discussed. Finally, we determine the upper limit on mh within the Minimal Supergravity (M-SUGRA) scenario up to the two-loop level, consistent with radiative electroweak symmetry breaking. We find an upper bound of mh \approx 127 GeV for mtop = 174.3 GeV in this scenario, which is slightly below the bound in the unconstrained MSSM.
If the soft Supersymmetry (SUSY) breaking masses and couplings are complex and cancelations do take place in the SUSY induced contributions to the fermionic Electric Dipole Moments (EDMs), then the CP-violating soft phases can drastically modify much of the known phenomenological pattern of the Minimal Supersymmetric Standard Model (MSSM). In particular, the squark loop content of the dominant Higgs production mechanism at the Large Hadron Collider (LHC), the gluon-gluon fusion mode, could be responsible of large corrections to the known cross sections.
We study neutral and charged Higgs boson production in association with stop and sbottom squarks at the Large Hadron Collider (LHC), within the so-called M-SUGRA scenario, i.e., the Supergravity (SUGRA) inspired Minimal Supersymmetric Standard Model (MSSM). For low values of \tanβonly the cases \tilde{t}_1\tilde{t}_1^* H, \tilde{t}_1\tilde{t}_1^* h and \tilde{t}_1\tilde{t}_2^* h give detectable rates while for \tanβgreater than 30 a variety of signals involving all Higgs bosons can be accessed, at high collider luminosity. The dependence of these reactions on the M-SUGRA parameters might further allow one to pin down the actual structure of the underlying Supersymmetric (SUSY) model.
The emergence of free fermionic string models with solely the MSSM charged spectrum below the string scale provides further evidence to the assertion that the true string vacuum is connected to the Z_2 x Z_2 orbifold in the vicinity of the free fermionic point in the Narain moduli space. An important property of the Z_2 x Z_2 orbifold is the cyclic permutation symmetry between the three twisted sectors. If preserved in the three generations models the cyclic permutation symmetry results in a family universal anomalous U(1)_A, which is instrumental in explaining squark degeneracy, provided that the dominant component of supersymmetry breaking arises from the U(1)_A D-term. Interestingly, the contribution of the family--universal D_A-term to the squark masses may be intra-family non-universal, and may differ from the usual (universal) boundary conditions assumed in the MSSM. We contemplate how D_A--term spectroscopy may be instrumental in studying superstring models irrespective of our ignorance of the details of supersymmetry breaking. We examine the possible effect of the intra--family non--universality on the resulting SUSY spectrum and the values of the strong coupling, effective weak mixing angle and W-gauge boson mass, up to a two loop accuracy, in the two models (universal and non-universal). We find that non universality relaxes the constraint of color and charge breaking minima which appears in the universal case. In addition, it predicts a 3% smaller value of α_s due to different threshold masses obtained in the latter scenario. Finally, we present the experimentally allowed predictions of the two models in an M_0 and M_{1/2} parameter space.