Focus Point Region Research Articles

REFINEMENTS IN EFFECTIVE POTENTIAL CALCULATIONS IN THE MSSM

The one-loop effective potential is a powerful tool in studying the electroweak symmetry breaking of supersymmetric theories, whose precise calculation may have important phenomenological consequences. In this work, we are correctly treating the contribution of the Higgs sector to the effective potential and refine the radiative corrections to the Higgs mixing parameter μ, which is known to affect greatly the supersymmetric spectrum. Working at the average stop scale to minimize the effect of the stop sector, we find additional corrections which can play a dominant role in the focus point region of the parameter space of the MSSM. The comparison of our results with those of the literature is discussed. We also discuss the gauge dependence of the effective potential and its effect on the μ parameter in analyses where this is determined from the one-loop minimization conditions of the effective potential.

Collider searches and cosmology in the MSSM with heavy scalars

In a variety of supersymmetric extensions of the standard model, the scalar partners of the quarks and leptons are predicted to be very heavy and beyond the reach of next-generation colliders. For instance, the realization of electroweak baryogenesis in supersymmetry requires new sources of $CP$ violation, which can only be naturally accommodated with electric dipole moment constraints if the first- and second-generation scalar fermions are beyond the TeV scale. Also, in focus-point supersymmetry and split supersymmetry the scalar fermions are very heavy. In this work, the phenomenology of scenarios with electroweak baryogenesis and in the focus-point region at the CERN LHC and ILC is studied, which becomes challenging due to the presence of heavy scalar fermions. Implications for the analysis of baryogenesis and dark matter are deduced. It is found that precision measurements of superpartner properties allow an accurate determination of the dark matter relic density in both scenarios, while important but only incomplete information about the baryogenesis mechanism can be obtained.

Model independent approach to focus point supersymmetry: from dark matter to collider searches

The focus point region of supersymmetric models is compelling in that it simultaneously features low fine-tuning, provides a decoupling solution to the SUSY flavor and CP problems, suppresses proton decay rates and can accommodate the WMAP measured cold dark matter (DM) relic density through a mixed bino-higgsino dark matter particle. We present the focus point region in terms of a weak scale parameterization, which allows for a relatively model independent compilation of phenomenological constraints and prospects. We present direct and indirect neutralino dark matter detection rates for two different halo density profiles, and show that prospects for direct DM detection and indirect detection via neutrino telescopes such as IceCube and anti-deuteron searches by GAPS are especially promising. We also present LHC reach prospects via gluino and squark cascade decay searches, and also via clean trilepton signatures arising from chargino-neutralino production. Both methods provide a reach out to m ∼ 1.7 TeV. At a TeV-scale linear e+e− collider (LC), the maximal reach is attained in the 12 or 13 channels. In the DM allowed region of parameter space, a (s)1/2 = 0.5 TeV LC has a reach which is comparable to that of the LHC. However, the reach of a 1 TeV LC extends out to m ∼ 3.5 TeV.

Likelihood analysis of the constrained minimal supersymmetric standard model parameter space

We present a likelihood analysis of the parameter space of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the input scalar masses m_0 and fermion masses m_{1/2} are each assumed to be universal. We include the full experimental likelihood function from the LEP Higgs search as well as the likelihood from a global precision electroweak fit. We also include the likelihoods for b to s gamma decay and (optionally) g_mu - 2. For each of these inputs, both the experimental and theoretical errors are treated. We include the systematic errors stemming from the uncertainties in m_t and m_b, which are important for delineating the allowed CMSSM parameter space as well as calculating the relic density of supersymmetric particles. We assume that these dominate the cold dark matter density, with a density in the range favoured by WMAP. We display the global likelihood function along cuts in the (m_{1/2}, m_0) planes for tan beta = 10 and both signs of mu, tan beta = 35, mu < 0 and tan beta = 50, mu > 0, which illustrate the relevance of g_mu - 2 and the uncertainty in m_t. We also display likelihood contours in the (m_{1/2}, m_0) planes for these values of tan beta. The likelihood function is generally larger for mu > 0 than for mu < 0, and smaller in the focus-point region than in the bulk and coannihilation regions, but none of these possibilities can yet be excluded.

WMAP constraints, supersymmetric dark matter, and implications for the direct detection of supersymmetry

Recently WMAP has measured the cosmological parameters to a much greater accuracy. We analyze the implications of this more precise measurement for supersymmetric dark matter and for the direct detection of supersymmetry at accelerators. We consider MSUGRA including also the hyperbolic branch (HB) in the radiative breaking of the electroweak symmetry. On the part of the hyperbolic branch where the lightest neutralino is dominantly a Higgsino rather than being mostly a B-ino, the relic density constraints are satisfied by coannihilation with the next lightest neutralino and the light chargino. Including this branch the lightest neutralino mass satisfies ${m}_{{\ensuremath{\chi}}_{1}^{0}}l~1200\mathrm{GeV}$ for $\mathrm{tan}\ensuremath{\beta}l~50.$ Constraints of $\stackrel{\ensuremath{\rightarrow}}{b}s+\ensuremath{\gamma},$ of ${g}_{\ensuremath{\mu}}\ensuremath{-}2,$ and of ${B}_{s}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ are also analyzed. It is shown that the neutralino-proton cross section in each case will fall within the reach of dark matter experiments. The possibility for the direct detection of supersymmetry is discussed in the allowed regions of the parameter space consistent with WMAP constraints. A brief discussion of the hyperbolic branch and focus point region (HB/FP) is also given.

Naturalness reach of the large hadron collider in minimal supergravity

We re-analyse the prospects of discovering supersymmetry at the LHC, in order to re-express coverage in terms of a fine-tuning parameter and to extend the analysis to scalar masses (m_0) above 2 TeV. We use minimal supergravity (mSUGRA) unification assumptions for the SUSY breaking parameters. The discovery reach at high m_0 is of renewed interest because this region has recently been found to have a focus point, leading to relatively low fine-tuning, and because it remains uncertain how much of the region can be ruled out due to lack of radiative electroweak symmetry breaking. The best fine tuning reach is found in a mono-leptonic channel, where for mu>0, A_0=0 and tan beta=10 (within the focus point region), and a top mass of 174 GeV, all points in mSUGRA with m_0 < 4000 GeV, with a fine tuning measure up to 210 (500) are covered by the search, where the definition of fine-tuning excludes (includes) the contribution from the top Yukawa coupling. Even for arbitrarily high m_0, mSUGRA can be discovered through gaugino events, provided the gaugino mass parameter M_1/2 < 460 GeV. In this region, the mono-leptonic channel still provides the best reach.