1. Compelling Scientific Questions The International Linear Collider will answer key questions about matter, energy, space and time We now sample some of these

2. Decoding Supersymmetry (SUSY) Supersymmetry provides a way to overcome inconsistencies in the standard model by introducing a new kind of space- time. But this requires that every known fundamental particle have a supersymmetric counterpart. Thus the partner of the spin ½ electron is a spin 0 ‘selectron’. All quarks also have their partners, as do the W and Z bosons, etc.

3. Decoding Supersymmetry The LHC is guaranteed to see the effects of supersymmetry, assuming SUSY has relevance for fixing the standard model. The counterparts of quarks and gluons will be produced copiously, but the LHC will not be sensitive to the partners of leptons, the photon or of the W/Z bosons. The ILC can produce the lepton, photon, and W/Z partners, AND determine their masses and quantum properties. If the matter-antimatter asymmetry in the universe arises from supersymmetry, the ILC can prove this to be the case.

4. Decoding Supersymmetry There are hundreds of variants of SUSY theories, and only detailed measurement of quantum numbers and masses of SUSY particles can determine the correct theory. The measured partner-particle masses can be extrapolated to high energy to reveal the theory at work. one example (other theories have different patterns): boson partners fermion partners superpartner masses energy

5. Understanding dark matter Our own and other galaxies are bound gravitationally by unseen dark matter, which predominates over ordinary matter by a factor of five. Its nature is unclear, but is likely to be due to very massive new particles created in the early universe. Supersymmetry figures in here, with the lightest SUSY particle (the neutralino) being an excellent candidate for dark matter. The LHC will find supersymmetry if it exists in nature, by producing partners of quarks and gluons that decay to other SUSY particles, including the neutralino.

6. Understanding dark matter ee e+e+ ++ ~  ~ ,Z ILC would copiously produce the partners of muons  which decay to muon + neutralino. The sharp edges in the muon energy distribution pin down the neutralino mass to 0.05% accuracy

7. If ILC agrees with Planck, then neutralino is likely the only dark matter particle. If ILC disagrees with Planck, then there are different forms of dark matter. Understanding dark matter ILC and satellite experiments WMAP and Planck provide complementary views of dark matter: while the ILC identifies the dark-matter particle, Planck is sensitive just to the total density of dark matter.

8. Understanding dark matter The mass of the neutralino measured at LHC is entangled with that of the superpartner quark (squark), and is poorly determined. The ILC measures the neutralino mass accurately, thereby allowing the LHC to extract the squark mass – an example of the synergy of the ILC and LHC. (Knowing the masses tells us how the supersymmetry is broken.) neutralino mass → squark mass → LHC squark mass without ILC LHC squark mass with ILC

9. Revealing the Higgs The Higgs field pervades all of space, interacting with quarks, electrons, etc. These interactions slow down particles as they move through space, effectively giving them mass. The Higgs field causes the Electromagnetic (long range) and Weak (short range) forces to differ at low energy. It provides at least one new particle (the Higgs boson) that has yet to be found. Different theories predict different types of Higgs bosons. The Higgs is somewhat like the Bunraku puppeteers, dressed in black to be ‘invisible’, manipulating the players in the drama.

10. If the Higgs decays to visible particles, the LHC will be able to measure its mass. But it will not determine its properties (intrinsic spin, etc.) and will not measure very well the strength of its interactions with other particles. collision energy interaction rate The ILC can ‘see’ the Higgs boson even if it decays only to invisible particles, and determine its quantum properties, and thereby point to its valid theoretical interpretation. Revealing the Higgs

11. supersymmetry baryogenesis Standard model values The ILC can measure the decay fractions of the Higgs into quarks, leptons, gluons and bosons. These decay fractions are the signatures that reveal the origin of the Higgs field. The pattern of deviations from expectations of the standard model tells us about the underlying more fundamental theory. Revealing the Higgs

12. Finding extra spatial dimensions String theory requires at least 6 extra spatial dimensions (beyond the 3 we already know). The extra dimensions are curled up like a mailing tube. If their radii are ‘large’ (~1/1000 of an atom), they could unify all forces (including gravity).

13. If a particle (e.g., a graviton) is created in a collision, it goes off into the extra dimensions, and becomes invisible in our world. Such events have lots of apparent “missing” energy and imbalance in total momentum. Both LHC and ILC can see such effects. Finding extra spatial dimensions

14. collision energy → production rate → LHC collisions of quarks span a range of energies, and thereby measure a combination of size and number of the “large” extra dimensions. The ILC with fixed (tuneable) energy of electron-positron collisions can provide a separate measure of size and number of large extra dimensions. Finding extra spatial dimensions

15. Wavefunctions trapped inside the ‘box’ of extra dimensions yield a series of resonance states that appear as particles decaying into e  e  or    . (But other new physical mechanisms could also provide such states.) The ILC can measure the ways such particles interact with electrons or muons. The colored regions indicate the expectation of three theories; the ILC can tell us which is correct! axial coupling vector coupling dimuon mass production rate Finding extra spatial dimensions

16. Seeking Unification At everyday energy scales, the 4 fundamental forces are quite distinct. At the Terascale, the EM and Weak forces unify as a result of the presence of the Higgs field. We see the possibility that these the Strong force may join the Electroweak at the grand unification scale. We dream that at the Planck scale, gravity may also join in.

17. Seeking Unification Increasing the energy scale for unification of forces corresponds to moving back to a time of the universe when a phase transition from symmetry to asymmetry took place, and structures like protons, atoms and galaxies first formed. The ILC is like a telescope that views that early universe. Learning about the phase transitions may shed light on dark energy or the issue of ‘inflation’.

18. Seeking Unification Present data show that the three forces (strong, EM, weak) have nearly the same strength at highest energy, possibly indicating their eventual unification A closer look shows it’s a near miss! force strength energy But with SUSY, the ILC and LHC can provide clear evidence for unification! g3g3 g3g3 g2g2 g2g2 g1g1 g1g1