1. Particle Physics: Status and Perspectives Part 9: Energy Frontier and Outlook
Manfred Jeitler
SS 2018

2. Supersymmetry

3. Supersymmetry
Every fundamental matter particle should have a massive "shadow" force carrier particle, and every force carrier should have a massive "shadow" matter particle.
This relationship between matter particles and force carriers is called supersymmetry.
For example, for every type of quark there may be a type of particle called a "squark."

4. Supersymmetry (“SUSY”)

5. Cancellation of quadratic terms (divergences)
source:
to avoid quadratic divergences in Higgs mass, otherwise ”fine-tuning” would be needed
“naturalness”

6. Running Coupling constants: Grand Unification
U(1) (hypercharge) SU(2) (left) SU(3) (color)
coupling constants get almost equal at high energies
but not quite, in Standard Model (left)
perfect match in Supersymmetry (right)

7. Parameters of the Standard Model
α1 = (5/3)g′2 /(4π) = 5α/(3 cos2 θW )
α2 = g2/(4π) = α/ sin2 θW
α3 = gs2/(4π)
α1(MZ) = 0.017
α2(MZ) = 0.034
α3(MZ) = ±
Parameters of the Standard Model
source:

8. dark matter: MACHOS vs WIMPS
massive astrophysical cosmic halo objects?
weakly interacting massive particles?
questions of cosmology to particle physics:
Why is there more matter than anti-matter in the universe?
What is the universe made of? What is dark matter?
What is dark energy?
answers to these questions concerning the largest scales might come from the physics of the smallest scales - elementary particle physics
matter/antimatter asymmetry:
seen in cosmological observations
fundamental for our existence
CP-violation indispensable
but the CP-violating effects known so far are much too weak
there must be other effects! (“strong CP-violation”)
dark matter and dark energy:
the mass of the universe (measured/observed from gravitational effects) is much higher than all the stars, dust, black holes and other known matter
therefore scientists are looking for this “dark matter”
MACHOS (Massive Astrophysical Compact Halo Objects) seem unlikely
WIMPS (Weakly Interacting Massive Particles) are what particle physicists are looking for
on top of this, there seems to be some extra unknown (“dark”) energy that makes the universe expand faster than it should, considering the amount of matter in it

9. how / what are WIMPs ? heavy neutral very weakly interacting
otherwise, they would be diluted
we see Dark Matter around galaxies
”cold” Dark Matter: ΛCDM
so, they cannot be neutrinos!
neutral
very weakly interacting

10. How to see SUSY decays
Supersymmetric (“SUSY”) particles could show very clear signatures due to cascade decays
but none have been found so far!

11. Dark Matter: WIMP searches
how do you find a WIMP?
exclude background  go underground
watch out for recoils
WIMP detectors:
big dual-phase noble gas volumes
crystals
idea: watch for two different signals
ionization
scintillation
energy deposition (“bolometer”)
so far: no WIMPs!

12. How is SUSY doing?
it is getting increasingly unlikely to find something that does all three jobs SUSY was invented for
fine-tuning / naturalness
grand unification
dark matter
but there might still be something out there that matches two of these ideas
to really “kill SUSY”, much higher energies would be needed than available at present-day colliders

13. no WIMPs  so maybe Axions ?
“Axions” were invented to solve the “strong CP problem”
why is CP conserved in strong interactions?
they would have to be very light (~meV)
could be “cooled” right after Big Bang by “dynamical friction”
after inflation

14. CAST experiment looking for solar axions at CERN

15. the graviton and gravitational waves
there are reasons to believe that the graviton as a particle cannot be seen
but gravitational waves have been seen!

16. Mass is always positive
Differently from electric charge, magnetic fields and color charge, there is no “negative” mass
Even antimatter has “positive” mass
Therefore there cannot be gravitational monopole or dipole fields
Have to look for quadrupole fields

19. Hulse-Taylor binary indirect demonstration of gravitational waves
Orbital decay of
PSR B The data points indicate the observed change in the epoch of periastron with date while the parabola illustrates the theoretically expected change in epoch according to general relativity.
Nobel prize 1993 to Hulse and Taylor
PSR B (also known as PSR J and PSR ) is a pulsar in a binary star system, in orbit with another neutron star around a common center of mass. In 1974 it was discovered by Russell Alan Hulse and Joseph Hooton Taylor, Jr., of Princeton University, a discovery for which they were awarded the 1993 Nobel Prize in Physics. It is also called the Hulse-Taylor binary pulsar after its discoverers.
pulse period is 59 milliseconds
orbit period is 7.75 hours

20. Michelson interferometer

21. LIGO (Laser Interferometer Gravitational Wave Observatory, USA)
measurement of gravitational waves
The gravitational interaction is so weak that the “graviton” which is supposed to mediate it has not been found yet. The effects are very small and demand very accurate detectors and an extremely good compensation of interfering environmental effects. Gravitational waves were observed for the first time last fall.
LIGO (Laser Interferometer Gravitational Wave Observatory, USA)

22. First measurement of gravitational waves

23. First measurement of gravitational waves

24. First measurement of gravitational waves

25. Binary neutron star inspiral
GW170817
On August 17, 2017 at 12∶41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per
80’000 years.

29. important questions of today’s particle physics
(ongoing research)
• Why are particle masses so different?
• Is there an overall (hidden) symmetry such as Supersymmetry (SUSY)  “mirror world” of all known particles?.
What is the nature of “Dark Matter” and “Dark Energy” in the universe?
• Why is there more matter than anti-matter?
• Why have neutrinos such small mass?
• Is there a Grand Unification which combines all interactions, including gravitation?
• Are there extra dimensions, D > 4 ? ( string theory, …)