Y. Santoso

Coannihilation effects in supergravity and D-brane models

Abstract Coannihilation effects in neutralino relic density calculations are examined for a full range of supersymmetry parameters including large tanβ and large A0 for stau, chargino, stop and sbottom coannihilation with the neutralino. Supergravity models possessing grand unification with universal soft breaking (mSUGRA), models with nonuniversal soft breaking in the Higgs and third generation sparticles, and D-brane models with nonuniversal gaugino masses were analysed. Unlike low tanβ where m0 is generally small, stau coannihilation corridors with high tanβ are highly sensitive to A0, and large A0 allows m0 to become as large asxa01xa0TeV. Nonuniversal soft breaking models at high tanβ also allow the opening of a new annihilation channel through the s-channel Z pole with acceptable relic density, allowing a new wide band in the m0–m1/2 plane with m1/2≳400xa0GeV and m0 rising toxa01xa0TeV. The D-brane models considered possess stau coannihilations regions similar to mSUGRA, as well as small regions of chargino coannihilation. Neutralino–proton cross sections are analysed for all models and it is found that future detectors for halo wimps will be able to scan essentially the full parameter space with m1/2

Neutralino–proton cross sections in supergravity models

Abstract The neutralino–proton cross section is examined for supergravity models with R-parity invariance with universal and non-universal soft breaking. The region of parameter space that dark matter detectors are currently (or will be shortly) sensitive, i.e., (0.1−10)×10 −6 pb, is examined. For universal soft breaking (mSUGRA), detectors with sensitivity σ χ 1 0 −p ≥1×10 −6 pb will be able to sample parts of the parameter space for tan β≳25 . Current relic density bounds restrict m χ 1 0 ≤120 GeV for the maximum cross sections, which is below where astronomical uncertainties about the Milky Way are relevant. Nonuniversal soft breaking models can allow much larger cross sections and can sample the parameter space for tan β≳4 . In such models, m 0 can be quite large reducing the tension between proton decay bounds and dark matter analysis. We note the existence of two new domains where coannihilation effects can enter, i.e., for mSUGRA at large tan β , and for nonuniversal models with small tan β .

Muon g−2, dark matter detection and accelerator physics

Abstract We examine the recently observed deviation of the muon g −2 from the Standard Model prediction within the framework of gravity mediated SUGRA models with R-parity invariance. Universal soft breaking (mSUGRA) models, and models with nonuniversal Higgs and third generation squark/slepton masses at M G are considered. All relic density constraints from stau–neutralino co-annihilation and large tan β NLO corrections for b → sγ decay are included, and we consider two possibilities for the light Higgs: m h >114xa0GeV and m h >120xa0GeV. The combined m h , b → sγ and a μ bounds give rise to lower bounds on tan β and m 1/2 , while the lower bound on a μ gives rise to an upper bounds on m 1/2 . These bounds are sensitive to A 0 , e.g., for m h >114xa0GeV, the 95% C.L. is tan β >7(5) for A 0 =0(−4 m 1/2 ), and for m h >120 GeV, tan β >15(10). The positive sign of the a μ deviation implies μ >0, eliminating the extreme cancellations in the dark matter neutralino–proton detection cross section so that almost all the SUSY parameter space should be accessible to future planned detectors. Most of the allowed parts of parameter space occur in the co-annihilation region where m 0 is strongly correlated with m 1/2 . The lower bound on a μ then greatly reduces the allowed parameter space. Thus using 90% C.L. bounds on a μ we find for A 0 =0 that tan β ⩾10 and for tan β ⩽40 that m 1/2 =(290–550)xa0GeV and m 0 =(70–300)xa0GeV. Then the tri-lepton signal and other SUSY signals would be beyond the Tevatron Run II (except for the light Higgs), only the τ 1 and h and (and for part of the parameter space) the e 1 will be accessible to a 500xa0GeV NLC, while the LHC would be able to see the full SUSY mass spectrum.

SUSY phases, the electron electric dipole moment and the muon magnetic moment

The electron electric dipole moment (d_e) and the muon magnetic moment anomaly (a_{mu}) recently observed at BNL are analyzed within the framework of SUGRA models with CP violating phases at the GUT scale. It is seen analytically that even if d_e were zero, there can be a large Bino mass phase (ranging from 0 to 2 pi) with a corresponding large B soft breaking mass phase (of size ~ 114 GeV, b -> s gamma, etc.) and relic density constraints with all stau-neutralino co-annihilation processes are included in the analysis.

Neutralino Proton Cross Sections for Dark Matter in SUGRA and D-BRANE Models

Neutralino proton cross sections are examined for models with R-parity invariance with universal soft breaking (mSUGRA) models, nonuniversal SUGRA models, and D-brane models. The region of parameter space where current dark matter detectors are sensitive, i. e. 1 × 10−6 pb. is examined. For in SUGRA models, detectors are sampling parts of the parametr space for tanβ ≳ 25. The nonuniversal models can achieve cross sections that are a factor of 10–100 bigger or smaller then the universal one and in the former case sample regions tanβ ≳ 4. The D-brane models considered require tanβ ≳ 15. The inclusion of CP violating phases reduces the cross section by a factor of ∼ 2–3 (but also requires considerable fine tuning at the GUT scale). The expected particle spectra at accelerators are examined and seen to differ for each model. Three new regions of possible coannihilation are noted.

Prospect for searches for gluinos and squarks at the Tevatron Tripler

Abstract We examine the discovery potential for SUSY new physics at a p p collider upgrade of Tevatron with s = 5.4 TeV and luminosity L ≃4×10 32 cm −2 s −1 (the Tripler). We consider the reach for gluinos ( g ) and squarks ( q ) using the experimental signatures with large missing transverse energy ( E / T ) of jets + E / T and 1l+ jets + E / T (where l is an electron or muon) within the framework of minimal supergravity. The Triplers strongest reach for the gluino is 1060 GeV for the jets + E / T channel and 1140 GeV for the 1l+ jets + E / T channel for 30 fb−1 of integrated luminosity (approximately two years running time). This is to be compared with the Tevatron where the reach is 440 (460) GeV in the jets + E / T channel for 15 (30) fb−1 of integrated luminosity.

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, MG. 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 MG (mSUGRA), the Higgs mass and b → sγ constraints imply that the gaugino mass, m1/2, obeys m1/2>300–400 GeV, putting most of the parameter space in the coannihilation domain, where there is a relatively narrow band in the m0-m1/2 plane. For μ>0, we find that the neutralino-proton cross section is ≳10−10 pb for m1/2<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 m1/2≲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.

Dark Matter in Supergravity

We consider neutralino-proton cross sections for halo dark matter neutralinos ( left( {tilde{chi }_{1}^{0}} right) ) within the framework of supergravity models with R-parity invariance for models with universal soft breaking (mSUGRA) and models with nonuniversal soft breaking. The analysis includes the necessary corrections to treat the large tanβ region (i.e. L-R mixing in the squark and slepton mass matrices, loop corrections to the b and τ masses,etc) and includes all coannihilation phenomena. For mSUGRA, dark matter detectors with current sensitivity are seen to be probing the region where tanβ ≳25, ( {{Omega }_{{tilde{chi }_{1}^{0}}}}{{h}^{2}} < 0.1,{{m}_{{tilde{chi }_{1}^{0}}}} lesssim 90GeV ), and for the light Higgs, m h ≲ 120 GeV. Nonuniversal models can have a much larger cross section, and current detectors can probe part of the parameter space where tans ≳ 4. Minimum cross sections are generally greater than 10–9 pb to 10–10 pb for m 1/2 = 600 GeV, (and hence accessible to planned future detectors), with the exception of a region when µ < 0 where for m 1/2 ≳ 450 GeV, 4 ≲ tanβ ≲ 20, the cross section drops to a minimum of about 1 × 10–12 pb at m 1/2 = 600 GeV, tanβ ⋍ 10. In this region, the gluino and squarks lie above 1 TeV, but should still be accessible to the LHC.

MUON g − 2 AND ELECTRIC DIPOLE MOMENTS IN SUGRA MODELS

The SUSY contribution to the muon magnetic moment anomaly, a_mu^SUGRA, and the electron electric dipole moment, d_e, is discussed within the framework of a modified mSUGRA model where the magnitudes of the soft breaking masses are universal, but arbitrary phases are allowed. It is shown analytically how the cancellation mechanism can allow for large phases (i.e. theta_B <~ 0.4) and still suppress the value of d_e below its current experimental bound. The dependence of a_mu^SUGRA on the CP violating phases are analytically examined, and seen to decrease it but by at most a factor of about two. This reduction would then decrease the upper bound on m_1/2 due to the lower bound of Brookhaven data, and hence lower the SUSY mass spectrum, making it more accessible to accelerators. At the electroweak scale, the phases have to be specified to within a few percent to satisfy the experimental bound on d_e, but at the GUT scale, fine tuning below 1% is required for lower values of m_1/2. This fine tuning problem will become more serious if the bound on d_e is decreased.