SUSY and Superstrings. Masahiro Yamaguchi Tohoku University Asian School Particles, Strings and Cosmology (NasuLec) September 25-28, [email protected], Japan. Phenomenology of SUSY and Superstrings. Masahiro Yamaguchi Tohoku University Asian School Particles, Strings and Cosmology (NasuLec)
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Gauge Coupling Unification
Gauge coupling constants change as energy scale changes
Minimal Supersymmetric Standard Model
Three couplings (SU(3), SU(2), U(1)) meet at one point ~1016 GeV
accidental? or suggests unification of forces in SUSY!?
I will discuss SUSY breaking masses problemSUSY breaking/Mediation mechanisms
Overview of Standard Model
Motivations for Beyond SM
Mediation Mechanisms of SUSY breaking
Phenomenology and Cosmology
Warped Extra Dimensions
KKLT set-up: low energy SUSY & Warped extra dim.
2.1 Great Success of Standard Model
Nature of forces
SU(3) x SU(2) x U(1)
force is mediated by gauge boson (vector boson)
e.g.) U(1) case
Coupling between matter and gauge boson: of string phenomenology
- solely controlled by the gauge invariance
(in renormalizable theory)
- characterized by charge (or representation) of matter
This has been intensively tested in electroweak sector at LEP/SLD experiments. ~90’s
The idea of gauge symmetry is established experimentally.
Gauge boson mass: of string phenomenology
Gauge boson mass term breaks gauge invariance.
How can we obtain gauge boson mass in a gauge invariant way?
based on spontaneous symmetry breaking
A vacuum is chosen at one point
Spontaneous Symmetry Breaking
Spontaneous symmetry breaking of global symmetry of string phenomenology Nambu-Goldstone boson
SSB of gauge symmetry
Would-be NG boson is absorbed into gauge boson
Gauge boson gets massive.
By chooing appropriately, one can eliminate 2.
gauge boson mass of string phenomenology
(coupling) x (charge)
x (order parameter)
physical degrees of freedom
Gauge symmetry beraking
Minimal Standard Model:
SU(2) doublet Higgs with Y=+1
Gauge-Higgs sector of string phenomenology
Masses of string phenomenology
Cf. Higgs production at e^+ e^- collider
3 would-be Nambu-Goldstone bosons
e.g. technicolor “techni-pions”
Two problems on dynamical symmetry breaking
Elementary Higgs in SM is the most economical way.
spontaneous gauge symmetry breaking
2) generates quark/lepton masses
Standard Model…. chiral gauge theory
RH quarks and LH quarks are in different
representation in SU(2) x U(1)
tightly related to SSB.
In SM, the interaction with Higgs yields quark/lepton masses
--- very natural and economical !
3 generations of string phenomenology
y_u and y_d : 3 x 3 matrices
CP violating phase (Kobayashi-Maskawa)
from weak eigenbasis to mass eigenbasis
No flavor-changing-neutral current (FCNC) at tree level
Gauge sym (coupling universality) is essential
W-boson coupling of string phenomenology
3 physical angles
1 physical CP phase
Flavor mixing is suppressed in SM of string phenomenology
Z-boson: no flavor mixing
W-boson: only source of flavor mixing
Examples of string phenomenology
No lepton flavor violation in SM
One can freely rotate mass eigenbasis of
precision test of electroweak theory @LEP/Tevatron
consistent with SM
works well K, B-mesons
EW data prefers light Higgs < 250 GeV or so.
Expects discovery at LHC (2007~)
Call for Beyond SM
Too many parameters
-- any rationale to explain them?
Gravity is not included consistently string theory?
Energy Scale of Standard Model of string phenomenology
Naturalness problem (gauge hierarchy problem)
1) of string phenomenologyContribution to gauge boson propagators
2) Flavor Problem in Beyond SM
Suppose there is new massive vector boson X with of string phenomenology
Exchange of X boson lepton flavor violation
four fermi interaction
We should seek for model
Low-energy SUSY is such a framework.