SUSY Particles Research Articles

Nonperturbative effect on dark matter annihilation and gamma ray signature from the galactic center

Detection of gamma rays from dark matter annihilation in the galactic center is one of the feasible techniques to search for dark matter. We evaluate the gamma ray flux in the case that the dark matter has an electroweak SU(2)_L charge. Such dark matter is realized in the minimal supersymmetric standard model (MSSM) when the lightest SUSY particle is the Higgsino- or Wino-like neutralino. When the dark matter is heavy compared to the weak gauge bosons, the leading-order calculation of the annihilation cross sections in perturbation breaks down due to a threshold singularity. We take into account non-perturbative effects by using the non-relativistic effective theory for the two-body states of the dark matter and its SU(2)_L partner(s), and evaluate precise cross sections relevant to the gamma ray fluxes. We find that the annihilation cross sections may be enhanced by several orders of magnitude due to resonances when the dark matter mass is larger than 1 TeV. Furthermore, the annihilation cross sections in the MSSM may be changed by factors even when the mass is about 500 GeV. We also discuss sensitivities to gamma ray signals from the galactic center in the GLAST satellite detector and the large Air Cerenkov Telescope arrays.

Muon g-2 constraints on SUSY dark matter reviewed and predicted

A summary of experimental results and theoretical calculations related to the muon anomalous magnetic moment. Assuming that a discrepancy with the Standard Model is due to contributions from supersymmetric particles provides a framework which can be used to constrain the mass of the dark matter particles, assumed to be the lightest neutral supersymmetric particles. A new g-2 run in the near future, coupled with expected theoretical advances, would result in a 5 σ discrepancy if the mean Δ a μ remains the same. In this case, we would expect to see SUSY particles at the LHC and use the g-2 results to measure tan β. If, instead, the Standard Model is confirmed to this precision, gauginos must have masses higher than ∼500 GeV/c 2 and simple SUSY dark matter models will be strained.

Direct detection of the Wino and Higgsino-like neutralino dark matter at one-loop level

The neutralino-nucleon (\tilde{\chi}^0-N) scattering is an important process for direct dark matter searches. In this paper we discuss one-loop contributions to the cross section in the wino-like and Higgsino-like LSP cases. The neutralino-nucleon scattering mediated by the Higgs \tilde{\chi}^0\tilde{\chi}^0 and Z\tilde{\chi}^0\tilde{\chi}^0 couplings at tree level is suppressed by the gaugino-Higgsino mixing at tree level when the neutralino is close to a weak eigenstate. The one-loop contribution to the cross section, generated by the gauge interaction, is not suppressed by any SUSY particle mass or mixing in the wino- and Higgsino-like LSP cases. It may significantly alter the total cross section when \sigma_{\tilde{\chi}^0 N}\sim 10^{-45} cm^2 or less.

Supersymmetry production from a TeV scale black hole at CERN LHC

If the fundamental Planck scale is near a TeV, then we should expect to see TeV scale black holes at the CERN LHC. Similarly, if the scale of supersymmetry (SUSY) breaking is sufficiently low, then we might expect to see light supersymmetric particles in the next generation of colliders. If the mass of the supersymmetric particle is of order a TeV and is comparable to the temperature of a typical TeV scale black hole, then such sparticles will be copiously produced via Hawking radiation: The black hole will act as a resonance for sparticles, among other things. In this paper we compare various signatures for SUSY production at LHC, and we contrast the situation where the sparticles are produced directly via parton fusion processes with the situation where they are produced indirectly through black hole resonances. We found that black hole resonances provide a larger source for heavy mass SUSY (squark and gluino) production than the direct perturbative QCD-SUSY production via parton fusion processes depending on the values of the Planck mass and black hole mass. Hence black hole production at LHC may indirectly act as a dominant channel for SUSY production. We also found that the differential cross sectionmore » d{sigma}/dp{sub t} for SUSY production increases as a function of the p{sub t} (up to p{sub t} equal to about 1 TeV or more) of the SUSY particles (squarks and gluinos), which is in sharp contrast with the pQCD predictions where the differential cross section d{sigma}/dp{sub t} decreases as p{sub t} increases for high p{sub t} about 1 TeV or higher. This is a feature for any particle emission from a TeV scale black hole as long as the temperature of the black hole is very high ({approx}TeV). Hence the measurement of increase of d{sigma}/dp{sub t} with p{sub t} for p{sub t} up to about 1 TeV or higher for final state particles might be a useful signature for black hole production at LHC.« less

PARTICLE SPECTRUM OF THE SUPERSYMMETRIC STANDARD MODEL FROM THE MASSLESS EXCITATIONS OF A FOUR-DIMENSIONAL SUPERSTRING

A superstring action is quantised with Neveu–Schwarz (NS) and Ramond (R) boundary conditions. The zero mass states of the NS sector are classified as the vector gluons, W-mesons, Bμ-mesons and scalars containing Higgs. 15 zero mass fermions are obtained from the Ramond sector. A spacetime supersymmetric Hamiltonian of the Standard Model is presented without any conventional SUSY particles.

Two Photon Background and the Reach of a Linear Collider for Supersymmetry in WMAP Favoured Coannihilation Regions

A neutralino relic density in accord with WMAP measurements can be found in the minimal supergravity (mSUGRA) model in several regions of parameter space: the stau co-annihilation corridor at low m_0 and the hyperbolic branch/focus point (HB/FP) region at large m_0 at the edges of parameter space, and the bulk and Higgs boson funnel regions within. In the regions at the edge, the mass gap between the next-to-lightest SUSY particle (NLSP) and the lightest SUSY particle (LSP) becomes small, and backgrounds from $\gamma\gamma\to f\bar{f}$ ($f$ is a SM fermion) become important for NLSP detection at an $e^+e^-$ linear collider. We evaluate these backgrounds from bremsstrahlung and beamstrahlung photons, and demonstrate that these do not preclude the observability of the signal for the cases where either the stau or the chargino is the NLSP. We also delineate the additional portion of the stau coannihilation region, beyond what can be accessed via a search for selectrons and smuons, that can be probed by a search for di-tau-jet events plus missing energy. The reach of a LC for SUSY in the HB/FP region is shown for an updated value of $m_t\simeq 180$ GeV as recently measured by the $D\O$ experiment.

Gluino annihilations and neutralino dark matter

We consider supersymmetric (SUSY) scenarios, compatible with all cosmological and phenomenological requirements, where the lightest SUSY particles (LSPs) are the neutralino and a quasidegenerate gluino. We study the neutralino relic abundance, focusing on gluino (co)annihilation effects. In case the neutralino is B-ino-like, in a wide mass window the relic abundance is naturally driven in the correct range for the LSP to be the main cold dark matter constituent. We show that the gluino is the strongest possible coannihilating partner of a B-ino-like neutralino in the general minimal supersymmetric standard model. Moreover, contrary to other coannihilation scenarios, gluino pair annihilations always dominate over coannihilation processes, even at relatively large gluino-neutralino mass splittings. Finally, we present prospects for neutralino dark matter detection in the outlined framework.

The ‘right’ sneutrino as the LSP

We show that the ‘right’ sneutrino can be the lightest supersymmetric particle. Clearly, this possibility will drastically change decay chains of SUSY particles. The sneutrino production at the next linear colliders has been analysed in this scenario.

Search for SUSY in the AMSB scenario with the DELPHI detector

The DELPHI experiment at the LEP e (+) e(-) collider collected almost 700 pb(-1) at centre-of-mass energies above the Z(0) mass pole and up to 208 GeV. Those data were used to search for SUSY in the Anomaly Mediated SUSY Breaking (AMSB) scenario with a flavour independent common sfermion mass parameter. The searches covered several possible signatures experimentally accessible at LEP, with either the neutralino, the sneutrino or the stau being the Lightest Supersymmetric Particle (LSP). They included: the search for nearly mass-degenerate chargino and neutralino, which is a typical feature of AMSB; the search for Standard-Model-like or invisibly decaying Higgs boson; the search for stable staus; the search for cascade decays of SUSY particles resulting in the LSP and a low multiplicity final state containing neutrinos. No evidence of a signal was found, and thus constraints were set in the space of the parameters of the model.

Constraining Z′ from supersymmetry breaking

We suggest and analyze a class of supersymmetric Z′ models based on the gauge symmetry U(1) x = xY−( B− L), where Y is the Standard Model hypercharge. For 1< x<2, the U(1) x D-term generates positive contributions to the slepton masses, which is shown to solve the tachyonic slepton problem of anomaly mediated supersymmetry breaking (AMSB). The resulting models are very predictive, both in the SUSY breaking sector and in the Z′ sector. We find M Z′ =2–4 TeV and the Z– Z′ mixing angle ξ⋍0.001. Consistency with symmetry breaking and AMSB phenomenology renders the Z′ “leptophobic”, with Br(Z′→ℓ +ℓ −)⋍(1–1.6)% and Br(Z′→q q ̄ )⋍44% . The lightest SUSY particle is either the neutral Wino or the sneutrino in these models.

Lepton Flavor Violation, Neutralino Dark Matter and the Reach of the LHC

We revisit the phenomenology of the Constrained MSSM with right-handed neutrinos (CMSSMRN). A supersymmetric seesaw mechanism, generating neutrino masses and sizable lepton flavour violating (LFV) entries is assumed to be operative. In this scheme, we study the complementarity between the `observable ranges' of various paths leading to the possible discovery of low energy SUSY: the reach of the Cern Large Hadron Collider (LHC), the quest for neutralino dark matter signals and indirect searches through LFV processes. Within the regions of the CMSSMRN parameter space compatible with all cosmo-phenomenological requirements, those which are expected to be probed at the LHC will be typically also accessible to upcoming LFV experiments. Moreover, parameter space portions featuring a heavy SUSY particle spectrum could be well beyond LHC reach while leaving LFV searches as the only key to get a glimpse on SUSY.

TeV-scale horizontal symmetry and the slepton mass problem of anomaly mediation

We propose a new scenario for solving the tachyonic slepton mass problem of anomaly mediated supersymmetry breaking models with a non-Abelian horizontal gauge symmetry broken at the TeV scale. A specific model based on SU(3) H horizontal symmetry is presented wherein the sleptons receive positive mass-squared from the asymptotically free SU(3) H gauge sector. Approximate global symmetries present in the model strongly suppress flavor changing processes induced by the horizontal vector gauge bosons. The model predicts m h ≲120 GeV for the lightest Higgs boson mass, tan β≃4, and M V =1–4 TeV for the SU(3) H gauge boson masses. The lightest SUSY particle is found to be the neutral wino, which is a candidate for cold dark matter.

Lower limit on the neutralino mass in the general MSSM

We discuss constraints on SUSY models with non-unified gaugino masses and R_P conservation. We derive a lower bound on the neutralino mass combining the direct limits from LEP, the indirect limits from gmuon, bsgamma, Bsmumu and the relic density constraint from WMAP. The lightest neutralino (mneutralino=6GeV) is found in models with a light pseudoscalar with MA<200GeV and a large value for $tan\beta$. Models with heavy pseudoscalars lead to mneutralino>18(29)GeV for $\tan\beta=50(10)$. We show that even a very conservative bound from the muon anomalous magnetic moment can increase the lower bound on the neutralino mass in models with mu<0 and/or large values of $\tan\beta$. We then examine the potential of the Tevatron and the direct detection experiments to probe the SUSY models with the lightest neutralinos allowed in the context of light pseudoscalars with high $\tan\beta$. We also examine the potential of an e+e- collider of 500GeV to produce SUSY particles in all models with neutralinos lighter than the W. In contrast to the mSUGRA models, observation of at least one sparticle is not always guaranteed.

Inclusive double diffractive production of SUSY particles at the LHC

We estimate the inclusive double diffractive production of SUSY particles at the LHC using a modified version of the POMWIG Monte Carlo event generator. The diffractive events are produced via the Ingelman–Schlein model for double pomeron exchange. The MSSM parameter space is scanned using the “Snowmass benchmark points” and it is shown that the lightest Higgs boson is the only SUSY particle with a large enough rate to be detected using these diffractive events.

WMAPing out supersymmetric dark matter and phenomenology

The recent WMAP data provide a rather restricted range of the Cold Dark Matter (CDM) density ΩCDMh2 of unprecedented accuracy. We combine these new data along with data from BNL E821 experiment measuring (gμ−2), the b→sγ branching ratio and the light Higgs boson mass bound from LEP, to update our analysis of the allowed boundaries in the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM). The prospects of measuring Supersymmetry at LHC look like a very safe bet, and the potential of discovering SUSY particles at a s=1.1 TeV linear collider is enhanced considerably. The implications for dark matter direct searches are also discussed.

Study of CMS sensitivity to neutrinoless τ decay at LHC

The Large Hadron Collider (LHC), scheduled to start operation in 2006, is foreseen to provide in the first year of running a total of ∼ 1012 τ leptons. CMS (Compact Muon Solenoid) is a general-purpose experiment designed to study proton-proton and heavy-ion collisions at LHC. Even if the Susy particles and Higgs searches together with the B-physics provide its main goal, the large number of τ-leptons provided, could allow a systematic study of tau-physics. We have performed a full simulation of CMS using GEANT 3 package and the object-oriented reconstruction program ORCA to study the sensitivity to neutrinoless tau decay τ → μ + μ − μ − and τ → μγ. We present the analysis developed for these channels and the results obtained.

Primordial nucleosynthesis and hadronic decay of supersymmetric particles in the early universe

In this talk, we consider the effects on big bang nucleosynthesis (BBN) of the hadronic decay of a long-lived SUSY particle, e.g., gravitino. If high-energy hadrons are emitted near the BBN epoch ( t ∼ 10 −2 − 10 2 sec), they extraordinarily inter-convert the background nucleons each other even after the freeze-out time of the neutron to proton ratio. Then, produced light element abundances are changed, and that may result in a significant discrepancy between standard BBN and observations. Especially on the theoretical side, now we can obtain a lot of experimental data of hadrons and simulate the hadronic decay process executing the numerical code of the hadron fragmentation even in the high energy region where we have no experimenta data. Using the computed light element abundances in the hadron-injection scenario, we derive a constraint on properties of such a SUSY particle by comparing our theoretical results with observations.

SPheno, a program for calculating supersymmetric spectra, SUSY particle decays and SUSY particle production at e+e− colliders

SPheno is a program that accurately calculates the supersymmetric particle spectrum within a high scale theory, such as minimal supergravity, gauge mediated supersymmetry breaking, anomaly mediated supersymmetry breaking, or string effective field theories. An interface exists for an easy implementation of other models. The program solves the renormalization group equations numerically to two-loop order with user-specified boundary conditions. The complete one-loop formulas for the masses are used which are supplemented by two-loop contributions in case of the neutral Higgs bosons and the μ parameter. The obtained masses and mixing matrices are used to calculate decay widths and branching ratios of supersymmetric particles as well as of Higgs bosons, b→ sγ, Δ ρ and ( g−2) μ . Moreover, the production cross sections of all supersymmetric particle as well as Higgs bosons at e + e − colliders can be calculated including initial state radiation and longitudinal polarization of the incoming electrons/positrons. The program is structured such that it can easily be extend to include non-minimal models and/or complex parameters.

SUSY Particles searches at LEP and interpretations within the MSSM

Searches for R-parity conserving supersymmetric particles have been performed in e +e − data collected by LEP detectors, at centre-of-mass energies up to 209 GeV, corresponding to an integrated luminosity of ∼3.1 fb −1. The results and their interpretation in the context of MSSM frameworks are briefly reviewed.

SUSY breaking mediation mechanisms and (g−2)μ,B→Xsγ,B→Xsl+l−andBs→μ+μ−

We show that there are qualitative differences in correlations among $(g-2)_{\mu}$, $B\to X_s \gamma$, $B \to X_{s} l^+ l^-$ and $B_s \to \mu^+ \mu^-$ in various SUSY breaking mediation mechanisms: minimal supergravity (mSUGRA), gauge mediation (GMSB), anomaly mediation (AMSB), gaugino mediation ($\tilde{g}$MSB), weakly and strongly interacting string theories, and $D$ brane models. After imposing the direct search limits on the Higgs boson and SUSY particle search limits and $B\to X_s \gamma$ branching ratio, we find all the scenarios can accommodate the $a_\mu \equiv (g-2)_\mu /2 $ in the range of (a few tens)$\times 10^{-10}$, and predict that the branching ratio for $B\to X_s l^+ l^-$ can differ from the standard model (SM) prediction by $\pm 20 %$ but no more. On the other hand, the $B_s \to \mu^+ \mu^-$ is sensitive to the SUSY breaking mediation mechanisms through the pseudoscalar and stop masses ($m_A$ and $m_{\tilde{t}_1}$), and the stop mixing angle. In the GMSB with a small messenger number, the AMSB, the $\tilde{g}$MSB and the noscale scenarios, one finds that $B(B_s \to \mu^+ \mu^-) \lesssim 2 \times 10^{-8}$, which is below the search limit at the Tevatron Run II. Only the mSUGRA or string inspired models can generate a large branching ratio for this decay.