Developments in Supergravity Unified Models
A review is given of developments in supergravity unified models proposed in 1982 and their implications for current and future experiment are discussed.
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arXiv subjects
Richard Arnowitt
Publications and source records attributed to Richard Arnowitt.
Determining the Dark Matter Relic Density in the Minimal Supergravity Stau-Neutralino Coannihilation Region at the Large Hadron Collider
We examine the stau-neutralino coannihilation (CA) mechanism of the early universe. We use the minimal supergravity (mSUGRA) model and show that from measurements at the Large Hadron Collider one can predict the dark matter relic density with an uncertainty of 6% with 30 fb-1 of data, which is comparable to the direct measurement by Wilkinson Microwave Anisotropy Probe. This is done by measuring four mSUGRA parameters m0, m1/2, A0 and tan(beta) without requiring direct measurements of the top squark and bottom squark masses. We also provide precision measurements of the gaugino, squark, and lighter stau masses in this CA region without assuming gaugino universality.
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Cosmology and Dark Matter at the LHC
We examine the question of whether neutralinos produced at the LHC can be shown to be the particles making up the astronomically observed dark matter. If the WIMP alllowed region lies in the SUGRA coannihilation region, then a strong signal for this would be the unexpected near degeneracy of the stau and neutralino i.e., a mass difference ΔM\simeq (5-15) GeV. For the mSUGRA model we show such a small mass difference can be measured at the LHC using the signal 3τ+jet+E_T^{\rm miss}. Two observables, opposite sign minus like sign pairs and the peak of the ττmass distribution allows the simultaneous determination of ΔM to 15% and the gluino mass M_{\tilde g} to be 6% at the benchmark point of M_{\tilde g}=850 GeV, A_0=0, μ>0 with 30 fb^{-1}. With 10 fb^{-1}, ΔM can be determined to 22% and one can probe the parameter space up to m_{1/2}=700 GeV with 100 fb^{-1}.
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$B_s - \bar B_s$ Mixing and Its Implication for $b \to s$ Transitions in Supersymmetry
We investigate the effect of the current measurement of the neutral $B_s$ meson mass difference, $ΔM_{B_s}$, on SUGRA models which have non-zero values of the soft breaking terms $(m^2_{LL,RR})_{23}$ and $A^{u,d}_{23}$ at the GUT scale. We use non-zero values of these parameter to explain the $B\to Kπ$ puzzle and find that even after satisfying the experimental result on $ΔM_{B_s}$ and the branching ratio (BR) of $b\to sγ$ we still can explain the puzzle. Further we show that in this parameter space it is possible to accommodate the large BR of $B\to η' K$ and the current experimental data for CP asymmetries of $B\to η' K^0$ and $B\to ϕK^0$. The predicted value of $\sin (2β^{\rm eff})_{η' K^0}$ is about $0.52-0.67$.
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Detection of SUSY in the Stau-Neutralino Coannihilation Region at the LHC
We study the feasibility of detecting the stau neutralino (stau_1-neutralino_1)coannihilation region at the LHC using tau leptons. The signal is characterized by multiple low energy tau leptons from neutralino_2-->tau stau_1-->tau tau neutralino_1 decays, where the stau_1 and neutralino_1 mass difference (Delta M) is constrained to be 5-15 GeV by current experimental bounds including the bound on the amount of neutralino cold dark matter. Within the framework of minimal supergravity models, we show that if hadronically decaying tau's can be identified with 50% efficiency for visible pt >20 GeV the observation of such signals is possible in the final state of two tau leptons plus large missing energy and two jets. With a gluino mass of 830 GeV the signal can be observed with as few as 3-10 fb^-1 of data (depending on the size of Delta M). Using a mass measurement of the tau pairs with 10 fb^-1 we can determine dM with a statistical uncertainty of 12% for Delta M = 10 GeV and an additional systematic uncertainty of 14% if the gluino mass has an uncertainty of 5%.
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The $B \to Kπ$ Puzzle and Supersymmetric Models
In the light of new experimental results on $B \to Kπ$ decays, we study the decay processes $B \to K π$ in the framework of both R-parity conserving (SUGRA) and R-parity violating supersymmetric models. We find that any possible deviations from the Standard Model indicated by the current data for the branching ratios and the direct CP asymmetries of $B \to Kπ$ can be explained in both R-parity conserving SUGRA and R-parity violating SUSY models. However, there is a difference between the predictions of both models to the time-dependent CP asymmetry observable $S_{K_{_S} π^0}$ whose current experimental results include large uncertainties. We demonstrate that this difference can be useful for testing both models with more accurate data for $S_{K_{S} π^0}$ and $A_{CP}^{+-}$ in the near future.
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The Stau Neutralino Co-annihilation Region at an International Linear Collider
We probe the stau-neutralino co-annihilation domain of the parameter space allowed by the current experimental bounds on the light Higgs mass, the b-> s γdecay, and the amount of neutralino cold dark matter within the framework of minimal SUGRA models at a 500 GeV e+e- linear collider. The most favorable signals of SUSY are stau pair production and neutralino pair production where the small mass difference between the lighter stau and the lightest neutralino in the co-annihilation region is ~5-15 GeV and hence generates low-energy tau leptons in the final state. This small mass difference would be a striking signal of many SUGRA models. We find that a calorimeter covering down to 1^o from the beams is crucial to reduce the two-photon background and the mass difference could be measured at a level of 10% with 500 fb^-1 of data where an invariant mass of two-tau jets and missing energy is used as a discriminator.
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Landau Pole Effects and the Parameter Space of the Minimal Supergravity Model
It is shown that analyses at the electroweak scale can be significantly affected due to Landau pole effects in certain regions of the parameter space. This phenomenon arises due to a large magnification of errors of the input parameters $m_t$, $α_G$ which have currently a 10 percent uncertainty in their determination. The influence of the Landau pole on the constraint that the scalar SUSY spectrum be free of tachyons is also investigated.It is found that this constraint is very strong and eliminates a large portion of the parameter space.Under the above constraint the trilinear soft SUSY breaking term at the electroweak scale is found to lie in a restricted domain.
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Constraints on the minimal supergravity model from the b->s+γdecay
The constraints on the minimal supergravity model from the b->s+γdecay are studied. A large domain in the parameter space for the model satisfies the CLEO bound, BR(b->s+γ)<5.4X10^{-4}. However, the allowed domain is expected to diminish significantly with an improved bound on this decay. The dependence of the b->s+γbranching ratio on various parameters is studied in detail. It is found that, for A_t<0 and the top quark mass within the vicinity of the center of the CDF value, m_t^{pole}=174\pm17 GeV, there exists only a small allowed domain because the light stop is tachyonic for most of the parameter space. A similar phenomenon exists for a lighter top and A_t negative when the GUT coupling constant is slightly reduced. For A_t>0, however, the branching ratio is much less sensitive to small changes in m_t, and α_G.
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Very Large Intermediate Breaking Scale In The Gepner Three Generation Model
A detailed study of the intermediate symmetry breaking scale, via the renormalization group equations, for a three generation heterotic string model arising from the N=2 superconformal construction is reported. The numerical study shows that the model admits a very large intermediate breaking scale $\op{>}{\sim}1.0\times10^{16}$ GeV. The role of the gauge singlets in this model is studied, and it is found that these fields play a crucial role in determining the directions and the scale of the intermediate symmetry breaking. The importance of the mixing in generation space is also studied. The generation mixing terms are found to have special effects in the intermediate symmetry breaking. Remarkably these terms can produce some {\it new} Yukawa couplings (not present at the Planck scale) through loops. These couplings are in general very small compared to the ones with non-vanishing tree level values and thus offer a {\it new} mechanism to solve the lepton/quark mass hierarchy problem.
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\cl{\bf $τ\rightarrowμμ{\barμ}$ and $τ\rightarrowμe{\bar e}$ Decays in String Models with $\e6$ Symmetry
A detailed analysis on the rare $τ$ decay {\it via} $\taumue$ and $\taumus$ in the string models with $\e6$ symmetry is reported. It is found that $Γ(\taumue)\sim(6-7)Γ(\taumus)$ and these rates are in general about 1000 times less than that of $Γ(μ\rightarrow eγ)$. It is also found that the out-going muon in $\taumue$ is almost 100\% right-handed polarized and the out-going electrons would be predominately parallel to each other. These decay processes may be accessible at the SSC.
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