Physics Beyond the Standard Model. Marina Cobal Fisica Sperimentale Nucleare e Sub-Nucleare

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1 Physics Beyond the Standard Model Marina Cobal Fisica Sperimentale Nucleare e Sub-Nucleare

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6 Increasingly General Theories Grand Unified Theories of electroweak and strong interactions Supersymmetry Superstring Theories 10 dimensions with gravity Superstring Unification to M Theory

7 Running Coupling Constants Charged particles have virtual quantum allowed clouds around them of photons and electronpositron pairs. Colored particles have virtual gluons and q-anti-q pairs. So the total coupling at long distance or charge, is different from the coupling at short distance, where the the cloud is penetrated. Electromagnetic coupling α 1 increases with energy from 1/137 to 1/40 at GeV Unification Scale Strong coupling α 3 decreases from ~1 to 1/40 Weak coupling to W s is α 2. So couplings come together at unification scale

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9 Fundamental Particles for Unification Unification means that at a GUT scale, where masses can be ignored, all fundamental particles appear in the same multiplet. This allows their charges to be the same or given fractions of each other, and accounts for the proton and electron charge being equal. The particles from the SM to include for the first generation are the 16 (left handed): u r u g u b d r d g d b anti-(u r u g u b d r d g d b ) ν e e - anti-ν e e + Recently, neutrino oscillations and mass were found, adding the anti-ν e. In the GUT, there are vector bosons that take fundamental particles into another in the multiplet.

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16 A Bit of History of Unification Electricity unified with magnetism (M. Faraday and J. C. Maxwell). Relativity and General Relativity (A. Einstein). Quantum Mechanics (Planck, Bohr, Schrodinger and Heisenberg). Relativistic quantum mechanics (P. Dirac). Quantum Electrodynamics (R. Feynman, Tomonaga, Schwinger). Quarks and Quantum Chromodynamics (Nemann, M. Gell-Mann and G. Zweig). Unification of Electromagnetism with Weak Interactions to form Electroweak theory (S. Weinberg, A. Salam). Grand Unified Theories Supersymmetry Superstring Theory of Everything including gravity.

17 Particle Supersymmetry In a Grand Unified Theory, all quarks and leptons are in a generation are united into one family. The GUT gauge bosons transform one quark or lepton to another, such a gluon changing one color quark into another. Another symmetry would be to transform all gauge bosons to fermions with the same charges, and vice versa. Thus for every spin ½ fermion there would be a spin 0 boson with the same charges and flavor, and to every gauge boson, there would be a like charged and coupled spin ½ fermion. These look-alikes, except for spin, are called sparticles.

18 Conserved Supersymmetry If supersymmetryness is conserved, sparticles can only be created or destroyed in pairs Sparticles would then decay to the ordinary particles plus another sparticle, until they reach the lightest supersymmetric particle (LSP) The LSP should be neutral and is a leading dark matter candidate They should have masses about 1 TeV They should be produced in pairs at the LHC

19 Sparticle Names Thus with quarks there would be spin 0 squarks. Leptons would have spin 0 sleptons (selectron and sneutrino) The photon also would have a spin ½ photino The W s and Z s would have spin ½ Winos and Zinos (after Wess and Zumino) Spin 0 Higgs would have spin ½ Higgsinos In a supergravity theory, spin 2 gravitons have spin 3/2 gravitino look-alikes.

20 Why Supersymmetry (SUSY)? It s believers think it is a beautiful symmetry between fermions and bosons, and should be a part of nature. If the sparticles are at about 1 TeV, then the running coupling constants actually do meet at a GUT scale of GeV. GUT scale (mass) Higgs s would normally couple to the light SM Higgs and bring its mass up to the GUT scale. Adding sparticles to particles cancel this coupling to leave the SM Higgs light, solving the so-called Heirarchy problem. String Theory requires SUSY, again for similar cancellations.

21 Evolution of Gauge Couplings (reciprocals) Standard Model Supersymmetry

22 Minimal SUSY Standard Model The MSSM has two Higgs doublets, as opposed to the one in the standard model. The doublets also have distinct anti-higgs. Thus there are 8 Higgs particles. Three are eaten to make the W ± and Z massive. One makes the neutral mass generating Higgs. Four more are observable, of which two are charged.

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28 What is String Theory? It is the theory that elementary particles are really strings with tension, that obey relativity and quantum mechanics. By dispersing the particle away from a point, it avoids infinities in the treatment of gravity or gravitons by pointlike particles. The string size is close to the Planck size of cm, which is the smallest size where gravity becomes strong. To avoid anomaly infinities requires supersymmetry and 10 dimensions (1 time and 9 space dimensions). String theory then provides a quantum theory of gravity. Andre Neveu, John Schwarz, Michael Green and Pierre Ramond were founders.

29 John Schwarz and Ed Witten

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33 Types of Superstring Theories There are five superstring theories. There is one open superstring theory with left (L) moving waves (SO(32)). There are two closed superstring theories: Type IIA: L-R parity symmetric Type IIB: L only, parity violating There are two heterotic string theories of a product of a string theory in 26 dim (with L moving waves) x a superstring in 10 dim (with R moving waves). (SO(32)) and (E8 x E8).

34 Unification of Superstring Theories Recently, in the second string revolution, it was discovered that there are transformations between all five superstring theories. (Ed Witten) This means they are all views of a larger theory which is not well understood, but is called M theory. It may be in 11 dimensions. For further information, see run by Patricia Schwarz, John Schwarz s wife. The Elegant Universe by Brian Greene,

35 Towards Verification of Superstring Theory Since superstring theory included the three unified forces of GUTS and gravity, it has been called the Theory of Everything. It has not been possible to solve superstring theory to find a unique physical model. There are a half-million ways to topologically compactify the extra six dimensions to very short distances, and leave the four dimensional world that we live in. So many GUTS and breakup paths of GUTS to the SM are still possible

36 Verification of Superstring Theory The masses of sparticles are not well predicted. If they are in the TeV range, they will appear in the LHC. Once they are found, the NLC e+ e- collider will more precisely determine their properties. The convergence of the running coupling strengths at a GUT scale is more successful with SUSY particles than in the SM. If SUSY is found, it will be considered a success of string theory. If not found, it could spell its demise. The lightest neutral SUSY particle (LSP) could be dark matter, and there are experiments to directly detect them, but they will take a while to reach large enough scale.

37 Brane Solutions String Theories have membrane solutions The most used is that all our 4 dimensional world is a membrane in the 10 dimensional world. Open string ends are attached to the membrane. Quarks, leptons and interacting bosons for strong and electroweak particles are confined to the brane. But gravitons as closed strings can leave the brane and spread out in the extra dimensions.

38 Brane with attached string and graviton in extra dimension

39 Large Extra Dimension Models By experimental limits, extra dimensions could still be as large as 0.1 millimeter, and this will be tested by gravity, which behaves as F ~ M 1 M 2 / r n+2 for n extra dimensions, at r < R. In these, gravity could become strong at 1 TeV and unify with the other forces there. (Nima Arkani- Hamed, Dimopoulos and Dvali) The extra dimension could be curled up with 1 TeV excitations, or at the String or Planck Scale. The former would show up in experiment at Fermilab or the LHC as invisible missing energy disappearing into the extra dimensions in excitations there, or as one micro black hole a second being produced.

40 Plane Extra Dimension The extra dimension could be between two flat branes, one of which is physical, and one of which has gravity (unphysical brane). The gravity field exponentially decreases from the unphysical to the physical brane. Thus gravity appears weak to us on the physical brane, but is strong on the unphysical brane. Called the Randall-Sundrum model. The extra dimension models so far do not give GUT theories, spoiling the supersymmetry triumph of explaining the convergence of coupling constants at the GUT scale.

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