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## New Physics Scenarios

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**New Physics Scenarios**Jay Wacker SLAC SLAC Summer Institute August 5&6, 2009**When’s the revolution?**Any minute now! An unprecedented moment**“New Physics”:**A structural change to the Standard Model Lagrangian “Scenario”: “A sequence of events especially when imagined” What is a “New Physics Scenario”?**Parameters are “Unnatural”**To know what is possible Experiment doesn’t match theoretical predictions Reduce/Explain the multitude of parameters Let’s us know what we can look for in experiments Limited only by creativity and taste Best motivation Well defined and have good theoretical motivation Typically has limited success, frequently untestable Why New Physics? Four Paradigms**The Plan**Beyond the SM Physics is 30+ years old There is no one leading candidate for new physics New physics models draw upon all corners of the SM In 2 hours there will be a sketch some principles used in a half dozen paradigms that created hundreds of models and spawned thousands of papers**Outline**The Standard Model Motivation for Physics Beyond the SM Organizing Principles for New Physics New Physics Scenarios Supersymmetry Extra Dimensions Strong Dynamics**5 Particles**symmetry Couplings unification 3 Couplings x 3 15 Particles, 12 Force carriers 2700 Mystery of Generations: 4 forces, 20 particles, 20 parameters Standard Model: a story of economy**The Standard Model**... where we stand today**Motivations for Physics Beyond the Standard Model**The Hierarchy Problem Dark Matter Exploration**The Hierarchy Problem**The SM suffers from a stability crisis Higgs vev determined by effective mass, not bare mass Many contributions that must add up to -(100 GeV)2 =**A recasting of the problem:**Why is gravity so weak? Explain how to make GF large (i.e. v small) Explain why GN is so small (i.e. MPl large)**High scale is a “mirage”**Gravity is strong at the weak scale Need to explain how gravity is weakened 1998: Large Extra Dimensions (Arkani-Hamed, Dimopoulos, Dvali) 2001: Universal Extra Dimensions (Appelquist, Cheng, Dobrescu)**The Higgs is composite**Resolve substructure at small distances Why hadrons are lighter than Planck Scale 1978: Technicolor (Weinberg, Susskind) 1999: Warped Gravity (Randall, Sundrum) 2001: Little Higgs (Arkani-Hamed, Cohen, Georgi)**1981: Supersymmetric Standard Model**(Dimopoulos, Georgi) Fermion Scalar not special UV dynamics at Scalar Mass related to Fermion Mass Scalar Mass forbidden Shift Symmetry Supersymmetry 1974: Higgs as Goldstone Boson (Georgi, Pais) 2001: Little Higgs (Arkani-Hamed, Cohen, Georgi) Scalar Scalar A New Symmetry**Dark Matter**85% of the mass of the Universe is not described by the SM There must be physics beyond the Standard Model Cold dark matter Electrically & Color Neutral Cold/Slow Relatively small self interactions Interacts very little with SM particles No SM particle fits the bill**Relic density is “frozen in”**DM too dilute to find each other Reverse process energetically disfavored Increasing The WIMP Miracle DM was in equilibrium with SM in the Early Universe**Boltzmann Equation Solves for**Frozen out when**Exploration**We want to see what’s there! Muon, Strange particles, Tau lepton not predicted before discovery Serendipity favors the prepared!**Organizing Principles**Gauge Coupling Unification Anomaly Cancellation Flavor Symmetries Effective Field Theory Chirality for going beyond the SM**Can do independent phase rotations**Vector symmetry Axial symmetry Allows mass Forbids mass Chirality A symmetry acting a fermions that forbids masses**etc...**The Standard Model is a Gauged Chiral Theory All masses are forbidden by a gauge symmetry 15 different bilinears all forbidden The Standard Model force carriers forbid fermion masses**Electroweak Symmetry Breaking**Breaking of Chiral Symmetry Fermions pick up Dirac Masses**with**known as “irrelevant operators” Nonrenomalizable! Dynamics of light fields described by Only contribute as Effective Field Theory Take a theory with light and heavy particles If we only can ask questions in the range**We have only tested the SM to certain precision**How do we know that there aren’t those effects? We know the SM isn’t the final theory of nature We should view any theory we test as an “Effective Theory” that describes the dynamics Shouldn’t be constrained by renormalizability One way of looking for new physics is by looking for these nonrenormalizable operators**Baryon Number Violation**Lepton Number Violation Flavor Violation CP Violation Precision Electroweak Contact Operators Generic Operators Limits on Non-Renormalizable Operators**Gauge interactions destroy most of this symmetry**global symmetry U(N) symmetry Flavor Symmetries 45 Total fermions that look the same in the free theory Yukawa couplings break the rest... but they are the only source of U(3)5 breaking Symmetries that interchange fermions Turn off all the interactions of the SM = Free Theory**Higgs doesn’t change flavor, but other scalar field is a**disaster Unless Can diagonalize mass matrix with unitary transformations or Prevents Flavor Changing Neutral Currents Imagine two scalars with two sources of flavor breaking**An anomaly leads to a mass for a gauge boson**Anomaly Cancellation Quantum violation of current conservation**One easy way: only vector-like gauge couplings**SU(3) SU(3) U(1) SU(3) U(1) U(1) SU(3) SU(3) U(1) It works, but is a big constraint! Anomaly cancellation: but the Standard Model is chiral**1**Counts charged matter 40 30 Weak scale measurement 2 20 High scale particle content 10 3 (GeV) Gauge coupling unification: Our Microscope**Grand Unification**Gauge coupling unification indicates forces arise from single entity**Standard Model Summary**The Standard Model is chiral gauge theory It is an effective field theory It is anomaly free & anomaly cancellation restricts new charged particles Making sure that there is no new sources of flavor violation ensures that new theories are not horribly excluded SM Fermions fit into GUT multiplets, but gauge coupling unification doesn’t quite work**The Scenarios**Supersymmetry Extra Dimensions Technicolor Little Higgs Theories**Gauge**Higgs Fermions Supersymmetry Doubles Standard Model particles Susy Taxonomy Dirac pair of Higgsinos Sfermions Gauginos Squarks, Sleptons Gluino, Wino, Bino Needed for anomaly cancellation**Too good!**(Two loop beta functions, etc) But significantly better than SM or any other BSM theory Susy Gauge Coupling Unification Only need to add in particles that contribute to the relative running Gauge Bosons, Gauginos, Higgs & Higgsinos**SUSY Interactions**Rule of thumb: take 2 and flip spins**SUSY Breaking**SUSY is not an exact symmetry We don’t know how SUSY is broken, but SUSY breaking effects can be parameterized in the Lagrangian**Problem with Parameterized SUSY Breaking**There are over 100 parameters once Supersymmetry no longer constrains interactions Most of these are new flavor violation parameters or CP violating phases Horribly excluded Susy breaking is not generic!**Scalar Masses**Trilinear A-Terms Need to be Flavor Universal Couplings Approximate degeneracy of scalars Soft Susy Breaking Universality of soft terms i.e. Super-GIM mechanism**A new symmetry forbids these couplings:**Proton Stability New particles ⇒ new ways to mediate proton decay Supersymmetric couplings that violate SM symmetries Proton Pion Dangerous couplings Lightest Supersymmetric Particle is stable Must be neutral and colorless -- Dark Matter**Primoridal**Susy Breaking MSSM Mediation Mediation of Susy Breaking Susy breaking doesn’t occur inside the MSSM Felt through interactions of intermediate particles Studied to reduce the number of parameters Gauge Mediation Universal “Gravity” Mediation Anomaly Mediation Usually only 4 or 5 parameters... but for phenomenology, these are too restrictive**The Phenomenological MSSM**The set of parameters that are: Not strongly constrained Easily visible at colliders 5 First 2 generation sfermions are degenerate 5 3rd generation sfermions in independent 3 Gaugino masses are free 3 Independent A-terms proportional to Yukawas 4 Higgs Masses are Free 20 Total Parameters**Charginos & Neutralinos**The Higgsinos, Winos and Binos After EWSB: 2 Charge +1 Dirac Fermions 4 Charge 0 Majorana Fermions All mix together, but typically mixture is small Tend find charginos next to their neutralino brethren Neutralinos are good DM candidates**Elementary Phenomenology**Neutralinos Charginos Sleptons Squarks Gluinos Mass**Neutralinos**Charginos Sleptons Mass Collider signatures Trileptons+MET: If sleptons are available 3 Leptons + MET**Neutralinos**Charginos Sleptons Mass Collider signatures Trileptons+MET Without sleptons in the decay chain 30% leptonic Br of W, 10% leptonic Br of Z 3% Total Branching Rate**mSUGRA Search**Collider signatures Squark-Gluino Pairs: 3j +MET Squark Pairs: 2j +MET Gluino Pairs: 4j +MET**Higgs mass gain is only log**Fine tuning loss is quadratic Need a susy copy of quartic coupling, only gauge coupling works in MSSM Difficult to make the Higgs heavier than 125 GeV in MSSM The Higgs Mass Problem