Cosmic Positron Signature from Dark Matter in the Littlest Higgs Model with T-parity Masaki Asano The Graduate University for Advanced Studies Collaborated with Shigeki Matsumoto Nobuchika Okada Yasuhiro Okada hep-ph/0602157
WMAP Introduction (Wilkinson microwave anisotropy probe) cold dark matter candidate Neutral Stable Massive (100 GeV 1TeV) WINP (Weakly Interacting Massive Particle) beyond SM No WINP in SM ( WINP ) Supersymmetric Model (neutralino) Little Higgs Model with T-parity (heavy photon) H-C.Cheng and I.Low ( 03)
Dark Matter Search indirect direct Dark matter scatter off of a detector Search the positron flux Dark Matter annihilation Gamma rays Neutrino antiprotons positrons from Galactic center halo HEAT ( High Energy Antimatter Telescope ) Energy range (positron) PAMELA (Payload for Antimatter Exploration and Light-nuclei Astrophysics) Future experiments AMS-02 (Alpha Magnetic Spectrometer) ~30 GeV ~270 GeV ~ a TeV
Outline 1.Littlest Higgs Model with T-parity 2.Relic abundance of the dark matter 3.Positron signature 4. Summary
Littlest Higgs Model with T-parity
Low energy cutoff scenario related to quadratic Solve the problem of fine-tuning divergence around Λ1TeV a to the Higgs Constrained by EW Precision Test mass term 2 cutoff scale m 0 +δm 2 Little Higgs Model R.Barbieri and A.Strumia ( 00) Little Hierarchy Problem can also solve Higgs : a pseudo Nambu-Goldstone boson δm 2 Λ 2 cutoff scale W W H h + h h g 2 g 2 Higgs mass : protected at 1-loop quadratic divergence h
New particles are constrained by EW Precision Test constraint T-parity (Z 2 symmetry) resolve m Z has to be raised reintroduce fine-tuning SM Particles T-even New Particles T-odd provide Dark matter Candidate
Littlest Higgs Model SU(5)/SO(5) non-linear sigma model VEV New triplet Higgs boson SM Higgs doublet SU(5) [SU(2) U(1)] 2 (gauged) [SU(2) U(1)] (SM)
Kinetic Term gauge couplings of the SU(2) and U(1)
Littlest Higgs Model with T-parity (TeV) 10 1 T-even h T-parity Spectrum T-odd Φ W H, Z H A H B 1 (W 1 ) B 2 (W 2 ) Π ΩΠΩ Ω= diag.(1,1, 1,1,1) Dark matter candidate 0.1 W, Z Lightest T-odd
Relic Abundance of Dark Matter
Relic density cross section ~g 2 /v ~g 2 ~m h2 /v ~m W2 /v main There are s-channel poles If m AH > m h ~g 2 /v J.Hubisz and P.Meade ( 05) Relic density depends on m AH,m h
contour plot of the relic abundance U-branch S-channel pole line m h = 2m AH L-branch Cross section is very large Relic density is very small Allowed region for WMAP at 2σlevel Relic density cross section
Indirect Detection of the Dark Matter Using Cosmic Positrons
1~2 kpc Sun Annihilation e + Dark Matter Annihilation e + Halo solve the diffusion eq. positron flux Number density of positrons per unit energy Effect of inhomogeneity Boost Factor ( in the inflationary universe ) 2~5 V.Berezinsky et al ( 03)
computational procedure In a wide region of the parameter f, m h space 1.Calculate the production rate of e + 2.Solve the diffusion equation Obtain the flux of the signal positrons 3.Think of the Background ( 99) which are obtained by simulations positron fraction E.A.Baltz and J.Edsjo
positron fraction in 7 sample points (On the allowed region for WMAP) BF = 5
χ2 Analysis the number of positron events observed in the i-th bin χ 2 is proportional to BF 2 the number of events expected from the background contribution in the i-th bin. acceptance of PAMELA 20.5 cm 2 sr AMS-02 450 cm 2 sr assuming three years of data-taking
contour plot of χ 2 In the PAMELA with BF = 5 χ 2 = 33.9 95% confidence level In the AMS-02 with BF = 2
χ 2 Plot χ 2 depends on BF and m h 120 120 300 150 χ 2 plot ( along with the U- and L-branch ) within WMAP constraint
Possibility to Detect the Signal PAMELA f < 830GeV (m AH < 120GeV ) BF > 5 AMS-02 Wide range of the parameter space including the region BF = 1 95% confidence level contour within WMAP constraint
Impact of Higgs Phenomenology Invisible width in the U-branch (m h > 2m AH ) h A H A H up to 5 % LHC and ILC The measurement might be possible at a future muon collider
Summary We have studied the possibility to detect the A H dark matter in the littlest Higgs model with T-parity. In the PAMELA experiment, the dark matter signal may be detected when f < 830GeV (m AH < 120GeV ) and BF > 5. In AMS-02 experiments, The dark matter signal may be detected even if there is no enhancement from the boost factor.