SUSY AND COSMOLOGY Jonathan Feng UC Irvine SLAC Summer Institute 5-6 August 2003
Target Audience From the organizers: graduate students, junior postdocs ¾ experimentalists, ¼ theorists Students enjoy the lively discussion sections. (What about the lecturers? Ominous!) SUSY and Cosmology SSI03 Lecture 1 Feng 2
Why Cosmology? The standard model successfully explains all observed phenomena of fundamental particles to date. No! The standard model is a great triumph, but it also fails at the most basic level. At present, cosmology and astroparticle physics provide the best evidence for new particle physics. SUSY and Cosmology SSI03 Lecture 1 Feng 3
Why SUSY? Cosmology and the Weak Scale Exponential drop Exponential drop Freeze out Stock price ($) Freeze out time Universe cools, leaves a residue of dark matter with Ω DM ~ 0.1 (σ Weak /σ) 13 Gyr later, Martha Stewart sells ImClone stock the next day, stock plummets Coincidence? Maybe, but worth investigating! SUSY and Cosmology SSI03 Lecture 1 Feng 4
The Plan LECTURE 1 LECTURE 2 SUSY Essentials Neutralino Cosmology Relic Density Detection Gravitino Cosmology Relic Density Detection Particle/Cosmo Synergy SUSY and Cosmology SSI03 Lecture 1 Feng 5
SUSY Essentials Supersymmetry: a new spacetime symmetry { P µ, L i, K i } { P µ, L i, K i, Q α } Q α : bosons fermions. Each known particle requires a (new) superpartner. What does this have to do with the weak scale? The gauge hierarchy problem: Why is m h ~ 100 GeV << M Pl ~ 10 19 GeV? SUSY and Cosmology SSI03 Lecture 1 Feng 6
SUSY and the Gauge Hierarchy Classical SM SUSY = + + λ 2 e L λ λ e R = + ẽ L, ẽ R ẽ L, ẽ R soften divergence, remove unnaturalness Requirements: λ ẽ = λ e, m ẽ ~ m h SUSY and Cosmology SSI03 Lecture 1 Feng 7
Neutral SUSY Spectrum Spin U(1) M 1 SU(2) M 2 Up-type µ Down-type µ m ν m 3/2 2 G graviton 3/2 Neutralinos: {χ χ 1, χ 2, χ 3, χ 4 } G gravitino 1 B W 0 1/2 B Bino W 0 Wino H u Higgsino H d Higgsino ν 0 H u H d ν sneutrino SUSY and Cosmology SSI03 Lecture 1 Feng 8
R-parity and Stable LSPs One slight problem: proton decay p d R u R u s R e L + u L u π 0 Forbid this with R-parity conservation: R p = ( 1) 3(B-L)+2S SM particles have R p = 1, SUSY particles have R p = 1 Require Π R p = 1 at all vertices Consequence: the lightest SUSY particle (LSP) is stable! SUSY and Cosmology SSI03 Lecture 1 Feng 9
Models We expect the weakscale theory to be derived from a highenergy fundamental theory by RGEs. Gauge couplings increase masses; Yukawa couplings decrease masses Olive (2003) End result: typical LSPs: χ, τ R SUSY and Cosmology SSI03 Lecture 1 Feng 10
Minimal Supergravity The canonical SUSY model is msugra, specified by only 5 parameters (actually 6 see Lecture 2): { m 0, M 1/2, A 0, tanβ, sgn(µ) } τ LSP χ LSP It exhibits virtually all dark matter possibilities (if one looks hard enough!) LSP is usually χ LEP excluded SUSY and Cosmology SSI03 Lecture 1 Feng 11
SUSY Essentials: Summary SUSY predicts many new particles at the weak scale Proton decay LSP is stable Dark matter candidates: gravitino, sneutrino, neutralino High energy models neutralino SUSY and Cosmology SSI03 Lecture 1 Feng 12
The Boltzmann equation: Neutralino Cosmology Thermal Relic Density Dilution from expansion χχ f f f f χχ Change variables: New Boltzmann equation: Y Y eq until interaction rate drops below expansion rate SUSY and Cosmology SSI03 Lecture 1 Feng 13
Freeze Out A little more work (see Kolb and Turner) shows: But Kamionkowski, Jungman, Griest (1995) We naturally find Ωh 2 ~ 0.1! SUSY and Cosmology SSI03 Lecture 1 Feng 14
χχ Annihilation In more detail: Pandora s box! Neutralino annihilation is sensitive to many processes. Two classes: Fermion diagrams χ are Majorana fermions: Pauli S = 0 L cons P wave suppression Goldberg (1983) Ellis, Hagelin, Nanopoulos, Srednicki (1983) Gauge boson diagrams vanish for χ = pure Bino. SUSY and Cosmology SSI03 Lecture 1 Feng 15
Bulk Region Where can we get the correct Ωh 2? Various regions. In the bulk region, χ pure Bino. Ω DM < 0.3 lower bound on σv sfermion mass < 200 GeV χ mass < 200 GeV! Cosmology (seemingly) guarantees light SUSY! SUSY and Cosmology SSI03 Lecture 1 Feng 16
Focus Point Region Unfortunately, this assumes χ pure Bino. This is not necessarily true, even in simple models like msugra. Bulk region χ pure Bino mχ < 200 GeV Ωh 2 Feng, Matchev, Wilczek (2000) Focus point region χ Bino-Higgsino mχ < few TeV Nevertheless, Ωh 2 very constraining! (Often too much χ DM.) SUSY and Cosmology SSI03 Lecture 1 Feng 17
Co-annihilation Region If other superpartners are nearly degenerate with the χ LSP, they can help it annihilate χ τ τ τ Requires (very roughly) m < T ~ m χ /25 In co-annihilation region, m χ < 500 GeV γ τ LSP Co-annihilation region This way to Focus point region Bulk Co-annihilation region Bulk region region Light blue: pre-wmap Dark blue: post-wmap Ellis, Olive, Santoso, Spanos (2003) Ellis, Olive, Santoso, Spanos (2003) SUSY and Cosmology SSI03 Lecture 1 Feng 18
Neutralino Cosmology Dark Matter Detection Direct detection depends on χn scattering Indirect detection depends on χχ annihilation χχ γ in galactic center χχ e + in halo or both χχ ν in centers of the Sun and Earth SUSY and Cosmology SSI03 Lecture 1 Feng 19
χ Dark Matter: Direct Detection Spin-independent scattering most promising for SUSY Theorists: χq scattering Expts: χ nucleus scattering Meet in middle: χp scattering Stage 1 Stage 2 Stage 3 Baer, Balazs, Belyaev, O'Farrill (2003) Stage 1: CDMS, EDELWEISS, ZEPLIN1, DAMA Stage 2: CDMS2, EDELWEISS2, ZEPLIN2, CRESST2 Stage 3: GENIUS, ZEPLIN4, CRYOARRAY SUSY and Cosmology SSI03 Lecture 1 Feng 20
Indirect Detection Experiments SUSY and Cosmology SSI03 Lecture 1 Feng 21
Dark Matter Detection Discovery prospects before LHC Particle probes Direct DM detection Indirect DM detection Correct relic density detection promising! (Both require large χ- matter couplings) Detection methods complementary SUSY and Cosmology SSI03 Lecture 1 Feng 22
Neutralino Cosmology: Summary Neutralinos: excellent dark matter candidates Cosmology provides no useful upper bounds on SUSY masses, but Ω DM is highly constraining Detection not yet constraining, but prospects promising Particle/cosmo searches complementary (see Lecture 2) SUSY and Cosmology SSI03 Lecture 1 Feng 23