New Physics Scenarios
Jay Wacker
SLAC
SLAC Summer Institute
August 5&6, 2009
An unprecedented moment
When’s the revolution?
Any minute now!
What is a “New Physics Scenario”?
“New Physics”:
A structural change to the Standard Model Lagrangian
“Scenario”:
“A sequence of events especially when imagined”
Why New Physics?
Four Paradigms
Experiment doesn’t match theoretical predictions
Best motivation
Parameters are “Unnatural”
Well defined and have good theoretical motivation
Reduce/Explain the multitude of parameters
Typically has limited success, frequently untestable
To know what is possible
Let’s us know what we can look for in experiments
Limited only by creativity and taste
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
Standard Model: a story of economy
symmetry
15 Particles, 12 Force carriers
unification
2700
Couplings
x3
5 Particles
3 Couplings
Mystery of Generations:
4 forces, 20 particles, 20 parameters
The Standard Model
... where we stand today
Standard Model Charges
Field
Color
Weak
Hypercharge
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)
A New Symmetry
UV dynamics at
Fermion
not special
Scalar
Supersymmetry
Shift Symmetry
Scalar
Scalar Mass related to Fermion Mass
Scalar
Scalar Mass forbidden
1981: Supersymmetric Standard Model
(Dimopoulos, Georgi)
1974: Higgs as Goldstone Boson
(Georgi, Pais)
2001: Little Higgs
(Arkani-Hamed, Cohen, Georgi)
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
The WIMP Miracle
Increasing
DM was in equilibrium with SM in the Early Universe
Reverse process energetically disfavored
DM too dilute to find each other
Relic density is “frozen in”
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
for going beyond the SM
Chirality
Effective Field Theory
Flavor Symmetries
Anomaly Cancellation
Gauge Coupling Unification
Chirality
A symmetry acting a fermions that forbids masses
Can do independent phase rotations
Vector symmetry
Allows mass
Axial symmetry
Forbids mass
The Standard Model is a Gauged Chiral Theory
All masses are forbidden by a gauge symmetry
15 different bilinears all forbidden
etc...
The Standard Model force carriers forbid fermion masses
Electroweak Symmetry Breaking
Breaking of Chiral Symmetry
Fermions pick up Dirac Masses
Effective Field Theory
Take a theory with light and heavy particles
If we only can ask questions in the range
Dynamics of light fields described by
with
Only contribute as
Nonrenomalizable!
known as “irrelevant operators”
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
Limits on Non-Renormalizable Operators
Baryon Number Violation
Lepton Number Violation
Flavor Violation
CP Violation
Precision Electroweak
Contact Operators
Generic Operators
Flavor Symmetries
Symmetries that interchange fermions
Turn off all the interactions of the SM = Free Theory
U(N) symmetry
45 Total fermions that look the same in the free theory
global symmetry
Gauge interactions destroy most of this symmetry
Yukawa couplings break the rest...
but they are the only source of U(3)5 breaking
Prevents Flavor Changing Neutral Currents
Imagine two scalars with two sources of flavor breaking
Can diagonalize mass matrix with unitary transformations
Higgs doesn’t change flavor, but other scalar field is a disaster
Unless
or
Anomaly Cancellation
Quantum violation of current conservation
An anomaly leads to a mass for a gauge boson
Anomaly cancellation:
One easy way: only vector-like gauge couplings
but the Standard Model is chiral
U(1)
U(1)
SU(3)
U(1)
SU(3)
SU(3)
SU(3)
U(1)
SU(3)
It works, but is a big constraint!
Gauge coupling unification: Our Microscope
Counts charged matter
40
1
30
20
2
10
3
(GeV)
Weak scale measurement
High scale particle content
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
Supersymmetry
Doubles Standard Model particles
Susy Taxonomy
Fermions
Gauge
Higgs
Dirac pair of Higgsinos
Sfermions
Squarks, Sleptons
Gauginos
Gluino, Wino, Bino
Needed for anomaly cancellation
Susy Gauge Coupling Unification
Only need to add in particles that contribute to the relative running
Gauge Bosons, Gauginos, Higgs & Higgsinos
Too good!
(Two loop beta functions, etc)
But significantly better than SM or any other BSM theory
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!
Soft Susy Breaking
Universality of soft terms
i.e. Super-GIM mechanism
Need to be Flavor Universal Couplings
Scalar Masses
Trilinear A-Terms
Approximate degeneracy of scalars
Proton Stability
New particles ⇒ new ways to mediate proton decay
Pion
Proton
Supersymmetric couplings that violate SM symmetries
Dangerous couplings
A new symmetry forbids these couplings:
Lightest Supersymmetric Particle is stable
Must be neutral and colorless -- Dark Matter
Mediation of Susy Breaking
Susy breaking doesn’t occur inside the MSSM
Felt through interactions of intermediate particles
MSSM
Mediation
Primoridal
Susy Breaking
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
First 2 generation sfermions are degenerate
5
3rd generation sfermions in independent
5
Gaugino masses are free
3
Independent A-terms proportional to Yukawas
3
Higgs Masses are Free
20 Total Parameters
4
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
Mass
Neutralinos
Charginos
Sleptons
Squarks
Gluinos
Sleptons
Charginos
Neutralinos
Trileptons+MET: If sleptons are available
3 Leptons + MET
Mass
Collider signatures
Sleptons
Charginos
Trileptons+MET
Without sleptons in the decay chain
Mass
Neutralinos
Collider signatures
30% leptonic Br of W, 10% leptonic Br of Z
3% Total Branching Rate
Collider signatures
Gluino Pairs: 4j +MET
mSUGRA Search
Squark Pairs: 2j +MET
Squark-Gluino Pairs: 3j +MET
Away from mSUGRA Gluino Search
The Higgs Mass Problem
Need a susy copy of quartic coupling, only gauge coupling works in MSSM
Higgs mass gain is only log
Fine tuning loss is quadratic
Difficult to make the Higgs heavier than 125 GeV in MSSM
Susy is the leading candidate for BSM Physics
Gauge Coupling Unification
Dark Matter candidate
Compelling structure
Become the standard lamppost
Basic Susy Signatures away from mSUGRA
are still being explored
A lot of the qualitative signatures of Susy
appear in other models
Extra Dimensions Taxonomy
Large
ADD Models
Small
TeV
Flat
Curved
UEDs
RS Models
GUT Models
Kaluza-Klein Modes
The general method to analyze higher dimensional theories
Equations of Motion
One 5D field = tower of 4D fields
SM
Large Extra Dimensions
Gravity
Integrate out extra dimension
Set
n
1
L
1010 km
2
1 mm
3
10nm
4
10-2nm
5
100fm
6
1fm
Large Extra Dimension Signatures
Monophoton+MET
Large Extra Dimension Signatures
Black Holes at the LHC
for
BHs decay
thermally, violating all
global conservation laws
High multiplicity events
with lots of energy
Universal Extra Dimensions
All fields go in the bulk
SM
+Gravity
Standard Model has KK modes
Mass
Impose Dirichlet Boundary Conditions
UED KK Spectra
Levels are degenerate at tree level
All masses within 30% of each other!
(This is a widely spaced example!)
KK Parity
All odd-leveled KK modes are odd
SM and even-leveled KK modes are even
LKP is stable!
Usually KK partner of Hypercharge Gauge boson
Looks like a degenerate Supersymmetry spectrum
until you can see 2nd KK level
Typical UED Event
Pair produce colored 1st KK level
Each side decays separately
Difficult is in Soft Spectra
Randall Sundrum Models
TeV Scale Curved Extra Dimensions
UV Brane
IR Brane
Warp factor
At each point of the 5th dimension,
there is a different normalization of 4D lengths
Effects of the Warping
An IR brane scalar
Need to go to canonical normalization
All mass scales on IR brane got crunched by warp factor
Super-heavy IR brane Higgs becomes light!
Can put all fields on IR brane...
but just like low dimension operators get
scrunched, high dimension operators get enlarged!
Motivated putting SM fields in bulk except for the Higgs
SM Gauge
+ Fermions
Higgs boson
UV Brane
IR Brane
Now have SM KK modes, but no KK parity
Resonances not evenly spaced either
Get light KK copies of right-handed top
Tonnes of Theory & Pheno and Models for RS Models!
AdS/CFT
Theories in Anti-de Sitter space (RS metric)
Equivalent to 4D theories that are conformal (scale invariant)
5D description is way of mocking up complicated 4D physics!
Warping is Dimensional Transmutation
IR Brane is breaking of conformal symmetry
Technicolor Theories
Imagine there was no Higgs
QCD still gets strong and quarks condense
Condensate has SM gauge quantum numbers
Like the Higgs!
QCD confinement/chiral symmetry breaking
breaks electroweak symmetry
Technicolor is a scaled-up version of QCD
RS Models are the modern versions of Technicolor
In Technicolor theories
Not necessarily a Higgs boson
etc
Technirhos usually first resonance
Need to be lighter than 1 TeV
800 GeV
Mediate contributions to
90 GeV
with
Can push off the Technirhos
usually a scalar resonance becomes narrow
etc
3 TeV
600 GeV
90 GeV
starts playing the role of the Higgs
Requires assumptions about
technicolor dynamics
Would like to get scalars light
without dynamical assumptions
Higgs as a Goldstone boson
Higgs boson is a technipion
Pions are light because the are
Goldstone bosons of approximate symmetries
Goldstone bosons only have periodic potentials
f set by Technicolor scale
Little Higgs Theories
Special type of symmetry breaking
Looks like normal “Mexican hat” potential
Lots of group theory to get specific examples
All have some similar features
New gauge sectors
Vector-like copies of the top quarks
There are extended Higgs sectors
SU(2)L singlets, doublets & triplets
Conclusion
Beyond the Standard Model Physics is rich and diverse
Within the diversity there are many similar themes
These lectures were just an entry way into
the phenomenology of new physics
We’ll soon know which parts of these theories
have something to do with the weak scale
References
I. Rothstein
“TASI Lectures on Effective Field Theory”
hep-ph/0308286
J. Wells
“TASI Lecture Notes: Introduction to Precision Electroweak Analysis”
hep-ph/0512342
S. P. Martin
“Supersymmetry Primer”
hep-ph/9709356
R. Sundrum
“TASI 2004: To the Fifth Dimension and Back”
hep-ph/0508134
C. Csaki et al
“TASI lectures on electroweak symmetry breaking from extra dimensions”
hep-ph/0510275
G. Kribs
“TASI 2004 Lectures on the pheomenology of extra dimensions”
hep-ph/0605325
M. Schmaltz, D. Tucker-Smith
“Little Higgs Review”
hep-ph/0502182