A preponderance of scientific evidence over the last hundred years tells us that our galaxy is filled with an unknown substance called dark matter. In fact, there is five times as much dark matter in the universe than there is ordinary matter: we are swimming in an ocean of dark matter and we have no firm idea what it is. We suspect that dark matter is composed of undiscovered elementary particles whose properties may, in turn, unlock some of the most pressing open questions in fundamental physics. So why haven't we figured out how to study dark matter in the lab, and why should we be optimistic that we may make progress in the coming decades?

1. @ f l i p . t a n e d o UCR PHYSICS & ASTRONOMY
Flip Tanedo
September 29, 2022
Physics Department Colloquium
Loyola University
Why haven’t we discovered dark matter?
A modern view into theoretical scotohylology

2. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Hot off the press
I was not planning on talking about this… yet here we are
theguardian.com/commentisfree/2022/sep/26/physics-particles-physicists
2

3. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Outline
These pictures make sense, I promise
3
ot even in our current mathematical or physical models of the
s a large amount of stuff out there silently pulling on us, and
what it is. We can’t possibly claim to understand our universe
nding this huge part of it.
you start feeling paranoid about weird, dark, mysterious
around you, consider this: what if dark matter is something
is made of something that we have no direct experience with.
e haven’t seen before, and it might behave in ways we
d.
amazing potential that exists here.
matter is made of some new kind of particle that we are able
arness in high-energy colliders? Or what if in discovering
ure out something about the laws of physics we didn’t know
ch as a new fundamental interaction or a new way that the
ons can work? And what if this new discovery lets us
ar matter in new ways?
’ve been playing a game your whole life, and suddenly you
are special rules or special new pieces you could be playing
zing technology or understanding could be unlocked by
t dark matter is and how it works?
y in the dark about it forever. Just because it’s dark doesn’t
matter.
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
The Higgs Boson
In 2012 particle physicists announced the discovery of the Higgs boson to
great international fanfare. Almost nobody understood what the Higgs boson
was, but lots of people got very excited. The New York Times wrote that it
“represents the very best of what the process of science can offer to modern
civilization.” That’s right, the Higgs boson is apparently better than
computers, flushing toilets, and reality TV.35
So what is the Higgs boson? Here’s a quiz to test your knowledge. Take it
now and then again after you read this chapter. We hope that at the very least
your score will not decrease.
Cham & Whiteson , We Have No Idea; Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art

4. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
A realistic picture of dark matter

5. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
A cartoon picture of dark matter
we are here
dark matter

6. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
A cartoon picture of dark matter, zoomed out
Weare swimming in
an ocean of darkmatter

7. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
7
A representative picture of dark matter physicists
Weare swimming in
an ocean of darkmatter
Water?

8. @ f l i p . t a n e d o LOYOLA PHYSIC S SEMINAR 59
8
Assumption for this talk: dark matter exists
Cham & Whiteson , We Have No Idea
It’s something we haven’t seen before, and it might behave in ways we
haven’t imagined.
Think of the amazing potential that exists here.
What if dark matter is made of some new kind of particle that we are a
And we know roughly how much there is

9. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
9
Astronomy and cosmology: dark matter exists
Images: Je
ff
Filippini (Berkeley Cosmology 2005), NASA APOD 2006, NASA WMAP
15%
85%
Ordinary Matter: theory is not complete
ROTATION CURVES GRAVITATIONAL LENSING COSMIC MICROWAVE BACKGROUND
And we know roughly how much there is
In fact, dark matter is a key reason why our
universe even has galaxies (like our own!)
Dark Matter: at least one new particle

10. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
10
Astronomy and cosmology: dark matter exists
15%
85%
And we know roughly how much there is
The existence of a new form of matter is
the most conservative interpretation of
these observations
All known alternatives are far more radical
modi
fi
cations to the known laws of nature.

11. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
11
Astronomy and cosmology: dark matter exists
theguardian.com/commentisfree/2022/sep/26/physics-particles-physicists
15%
85%
And we know roughly how much there is
The existence of a new form of matter is
the most conservative interpretation of
these observations
Hossenfelder Op-Ed in The Guardian

12. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
12
Weare swimming in
an ocean of darkmatter
Water?
“Do science” options:
Canyou see it?
Canyou touch it?
Canyou hear it?
Canyou smellit?
Canyou taste it?
Be more clever.

13. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Image: Magnus Manske via Wikipedia U. Le Verrier; hubpages.com/education/The-Drama-of-Neptunes-Discovery
13
Astro observations + theory → missing stuff
Neptune: the first discovery of “dark matter”

14. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Hall Colby, Rochester NY, 1846
Vulcan: Le Verrier strikes again?
Puzzle: precession of the perihelion of Mercury

15. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Hall Colby, Rochester NY, 1846
Evolution vs. Revolution

16. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
16
‣ What it is
‣ How it got here
‣ Why it’s still here
‣ Why we haven’t found it
‣ How we will con
fi
rm it
Atheoryof darkmatter
remarkably constrained

17. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Outline
These pictures make sense, I promise
17
ot even in our current mathematical or physical models of the
s a large amount of stuff out there silently pulling on us, and
what it is. We can’t possibly claim to understand our universe
nding this huge part of it.
you start feeling paranoid about weird, dark, mysterious
around you, consider this: what if dark matter is something
is made of something that we have no direct experience with.
e haven’t seen before, and it might behave in ways we
d.
amazing potential that exists here.
matter is made of some new kind of particle that we are able
arness in high-energy colliders? Or what if in discovering
ure out something about the laws of physics we didn’t know
ch as a new fundamental interaction or a new way that the
ons can work? And what if this new discovery lets us
ar matter in new ways?
’ve been playing a game your whole life, and suddenly you
are special rules or special new pieces you could be playing
zing technology or understanding could be unlocked by
t dark matter is and how it works?
y in the dark about it forever. Just because it’s dark doesn’t
matter.
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
The Higgs Boson
In 2012 particle physicists announced the discovery of the Higgs boson to
great international fanfare. Almost nobody understood what the Higgs boson
was, but lots of people got very excited. The New York Times wrote that it
“represents the very best of what the process of science can offer to modern
civilization.” That’s right, the Higgs boson is apparently better than
computers, flushing toilets, and reality TV.35
So what is the Higgs boson? Here’s a quiz to test your knowledge. Take it
now and then again after you read this chapter. We hope that at the very least
your score will not decrease.
Cham & Whiteson , We Have No Idea; Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art

18. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Particle Physics, circa 1990s
18
/ /
¯ / − /
¯ / /
/ −/
¯ / −
/
/
( ) ( )
fundamental forces
matter
particles
or something to explain
unitarity of WW scattering
?
Image: Stanford ATLAS website
it mean? Who will help us in our hour of need? The answer is: the Higg
boson.
The Higgs Boson

19. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Particle Physicists
Cham and Whiteson, We Have No Idea
19
In Which You Learn You Are Quite Weird and
Special

20. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
20
Maximilien Brice, CERN via National Geographic (May 2012)

21. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
D. Overbye, New York Times, 4 July 2012
21

22. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Known Unknowns in Particle Physics
1990s - 2020; incomplete list
Images: Cham and Whiteson, We Have No Idea
22
Why is the Higgs boson light?
Hierarchy Problem
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
The Higgs Boson
In 2012 particle physicists announced the discovery of the Higgs boson to
great international fanfare. Almost nobody understood what the Higgs boson
was, but lots of people got very excited. The New York Times wrote that it
“represents the very best of what the process of science can offer to modern
civilization.” That’s right, the Higgs boson is apparently better than
computers, flushing toilets, and reality TV.35
So what is the Higgs boson? Here’s a quiz to test your knowledge. Take it
now and then again after you read this chapter. We hope that at the very least
your score will not decrease.
Why is there more matter than antimatter?
Why is ϴYM small? Strong CP Problem
What is the origin of neutrino mass?
Dark matter is not even in our current mathematical or physical models of the
universe. There is a large amount of stuff out there silently pulling on us, and
we don’t know what it is. We can’t possibly claim to understand our universe
without understanding this huge part of it.
Now, before you start feeling paranoid about weird, dark, mysterious
stuff floating all around you, consider this: what if dark matter is something
awesome?
Dark matter is made of something that we have no direct experience with.
It’s something we haven’t seen before, and it might behave in ways we
haven’t imagined.
Think of the amazing potential that exists here.
What if dark matter is made of some new kind of particle that we are able
to produce and harness in high-energy colliders? Or what if in discovering
what it is, we figure out something about the laws of physics we didn’t know
about before, such as a new fundamental interaction or a new way that the
existing interactions can work? And what if this new discovery lets us
manipulate regular matter in new ways?
Imagine you’ve been playing a game your whole life, and suddenly you
realize that there are special rules or special new pieces you could be playing
with. What amazing technology or understanding could be unlocked by
figuring out what dark matter is and how it works?
We can’t stay in the dark about it forever. Just because it’s dark doesn’t
mean it doesn’t matter.
What is dark matter?
Missing Mass Problem
Other puzzles (possibly related to dark matter?)

23. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
The story so far: supersymmetry
Images: Cham and Whiteson, We Have No Idea
23
mh ?
!
Missing Mass
ean? Who will help us in our hour of need? The answer is: the Higgs
on.
The Higgs Boson
012 particle physicists announced the discovery of the Higgs boson to
at international fanfare. Almost nobody understood what the Higgs boson
, but lots of people got very excited. The New York Times wrote that it
presents the very best of what the process of science can offer to modern
lization.” That’s right, the Higgs boson is apparently better than
mputers, flushing toilets, and reality TV.35
So what is the Higgs boson? Here’s a quiz to test your knowledge. Take it
w and then again after you read this chapter. We hope that at the very least
r score will not decrease.
Dark matter is not even in our current mathematical or physical models of the
universe. There is a large amount of stuff out there silently pulling on us, and
we don’t know what it is. We can’t possibly claim to understand our universe
without understanding this huge part of it.
Now, before you start feeling paranoid about weird, dark, mysterious
stuff floating all around you, consider this: what if dark matter is something
awesome?
Dark matter is made of something that we have no direct experience with.
It’s something we haven’t seen before, and it might behave in ways we
haven’t imagined.
Think of the amazing potential that exists here.
What if dark matter is made of some new kind of particle that we are able
to produce and harness in high-energy colliders? Or what if in discovering
what it is, we figure out something about the laws of physics we didn’t know
about before, such as a new fundamental interaction or a new way that the
existing interactions can work? And what if this new discovery lets us
manipulate regular matter in new ways?
Imagine you’ve been playing a game your whole life, and suddenly you
realize that there are special rules or special new pieces you could be playing
with. What amazing technology or understanding could be unlocked by
figuring out what dark matter is and how it works?
We can’t stay in the dark about it forever. Just because it’s dark doesn’t
mean it doesn’t matter.

24. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
The story so far: supersymmetry
24
mh ?
SUSY New Particles
p+ stability
R-parity
?
Dark Matter ?
Missing Mass

25. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
The story so far: supersymmetry
25
mh ?
SUSY New Particles
p+ stability
R-parity
?
Dark Matter ?
Missing Mass
‣What it is
‣ How it got here
‣Why it’s still here
‣ Why we haven’t found it
‣ How we will con
fi
rm it

26. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
The story so far: supersymmetry
26
mh ?
Dark Matter ?
Missing Mass
Weak scale mass ~100 GeV
Weak scale interaction strength GF
No additional parameters (roughly)
‣What it is
‣ How it got here
‣ Why it’s still here
‣Why we haven’t found it
‣ How we will con
fi
rm it

27. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Weakly-Interacting Massive Particle
27
mh ?
Dark Matter ?
Missing Mass
Weak scale mass ~100 GeV
Weak scale interaction strength GF
No additional parameters (roughly)
How much
dark matter?

28. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
28
Approx. 1 WIMP
per mug of coffee
~ GeV / cm3

29. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
How much dark matter is there? WIMP miracle
29
1 10
equilibrium
time ~ mass / temp
[comoving]
number
density
A N N I H I L AT I O N
SM
SM
H U B B L E
freeze out
SM
SM
SM
SM
=
E Q U I L I B R I U M
‣ What it is
‣How it got here
‣ Why it’s still here
‣ Why we haven’t found it
‣ How we will con
fi
rm it

30. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
The story so far: supersymmetry
30
mh ?
SUSY New Particles
p+ stability
R-parity
?
Dark Matter
with correct
abundance !

31. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
The story so far: extra dimensions
31
mh ?
Extra
Dimensions
New Particles
precision
observables
KK-parity
?
Dark Matter
with correct
abundance !
free in
fl
at XD
warped
extra dim.

32. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
The story so far: compositeness (substructure)
32
mh ?
composite New Particles
precision
observables
T-parity
?
Dark Matter
with correct
abundance !

33. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
The general story
33
mh ?
new symmetry New Particles
precision
observables
new parity
?
Dark Matter
with correct
abundance !
‣ What it is
‣ How it got here
‣ Why it’s still here
‣ Why we haven’t found it
‣How we will con
fi
rm it

34. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Direct Detection (n.)
via LUX-LZ (kipac.stanford.edu/research/topics/direct-dark-matter-detection)
Wait for a WIMP to hit a nucleus…
Underground,
high-volume,
high-sensitivity
Why large vats of xenon?
Hint: expected WIMP mass is
around 100x proton mass

35. @ f l i p . t a n e d o UCR PHYSICS & ASTRO COLLOQUIUM 59
Particle Data Group (2020)
35
strength
of
interaction
[cm
2
]
dark matter mass [GeV]
‣ What it is
‣ How it got here
‣ Why it’s still here
‣ Why we haven’t
found it
‣How we will
con
fi
rm it
‣How we falsi
fi
ed
it (mostly)
weak scale coupling
weak scale mass

36. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
A great love story
Andrew Grant, Science News, June 2013; cartoons: Cham and Whiteson, We Have No Idea
36
n? Who will help us in our hour of need? The answer is: the Higgs
The Higgs Boson
Dark matter is not even in our current mathematical or physical models of the
universe. There is a large amount of stuff out there silently pulling on us, and
we don’t know what it is. We can’t possibly claim to understand our universe
without understanding this huge part of it.
Now, before you start feeling paranoid about weird, dark, mysterious
stuff floating all around you, consider this: what if dark matter is something
awesome?
Dark matter is made of something that we have no direct experience with.
It’s something we haven’t seen before, and it might behave in ways we
haven’t imagined.
Think of the amazing potential that exists here.
What if dark matter is made of some new kind of particle that we are able
to produce and harness in high-energy colliders? Or what if in discovering
what it is, we figure out something about the laws of physics we didn’t know
about before, such as a new fundamental interaction or a new way that the

37. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
A great love story . . . and a break up
37
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
Dark matter is not even in our current mathematical or physical models of the
universe. There is a large amount of stuff out there silently pulling on us, and
we don’t know what it is. We can’t possibly claim to understand our universe
without understanding this huge part of it.
Now, before you start feeling paranoid about weird, dark, mysterious
stuff floating all around you, consider this: what if dark matter is something
awesome?
Dark matter is made of something that we have no direct experience with.
It’s something we haven’t seen before, and it might behave in ways we
haven’t imagined.
Think of the amazing potential that exists here.
What if dark matter is made of some new kind of particle that we are able
to produce and harness in high-energy colliders? Or what if in discovering
what it is, we figure out something about the laws of physics we didn’t know
… with apologies to Andrew Grant, Science News, June 2013; cartoons: Cham and Whiteson, We Have No Idea
2013
When I broke up with
the Higgs and
became a “dark
matter theorist”

38. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Outline
These pictures make sense, I promise
38
ot even in our current mathematical or physical models of the
s a large amount of stuff out there silently pulling on us, and
what it is. We can’t possibly claim to understand our universe
nding this huge part of it.
you start feeling paranoid about weird, dark, mysterious
around you, consider this: what if dark matter is something
is made of something that we have no direct experience with.
e haven’t seen before, and it might behave in ways we
d.
amazing potential that exists here.
matter is made of some new kind of particle that we are able
arness in high-energy colliders? Or what if in discovering
ure out something about the laws of physics we didn’t know
ch as a new fundamental interaction or a new way that the
ons can work? And what if this new discovery lets us
ar matter in new ways?
’ve been playing a game your whole life, and suddenly you
are special rules or special new pieces you could be playing
zing technology or understanding could be unlocked by
t dark matter is and how it works?
y in the dark about it forever. Just because it’s dark doesn’t
matter.
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
The Higgs Boson
In 2012 particle physicists announced the discovery of the Higgs boson to
great international fanfare. Almost nobody understood what the Higgs boson
was, but lots of people got very excited. The New York Times wrote that it
“represents the very best of what the process of science can offer to modern
civilization.” That’s right, the Higgs boson is apparently better than
computers, flushing toilets, and reality TV.35
So what is the Higgs boson? Here’s a quiz to test your knowledge. Take it
now and then again after you read this chapter. We hope that at the very least
your score will not decrease.
Cham & Whiteson , We Have No Idea; Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art

39. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art; photo courtesy of @neohumanity via Instagram
Have we been looking under the wrong lamp-post?
1. At least one new particle.
2. Mechanism to produce
𝜌
DM.
3. Experimental viability.
4. Strategy to test the model.

40. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art; photo courtesy of @neohumanity via Instagram
Have we been looking under the wrong lamp-post?
1. At least one new particle.
2. Mechanism to produce
𝜌
DM.
3. Experimental viability.
4. Strategy to test the model.
‣ What it is
‣ How it got here
‣ Why it’s still here
‣ Why we haven’t found it
‣ How we will con
fi
rm it
A theoryof dark matter

41. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art; photo courtesy of @neohumanity via Instagram
Have we been looking under the wrong lamp-post?
non-thermal production
complicated dark sectors
decaying dark matter
macroscopic dark matter lumps
primordial black holes
axions, ultralight dark matter
gravity is very weird
many other possibilities…
1. At least one new particle.
2. Mechanism to produce
𝜌
DM.
3. Experimental viability.
4. Strategy to test the model.

42. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art; photo courtesy of @neohumanity via Instagram
Have we been looking under the wrong lamp-post?
non-thermal production
complicated dark sectors
decaying dark matter
macroscopic dark matter lumps
primordial black holes
axions, ultralight dark matter
gravity is very weird
many other possibilities…
Hossenfelder, theguardian.com/commentisfree/2022/
sep/26/physics-particles-physicists

43. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art; photo courtesy of @neohumanity via Instagram
Have we been looking under the wrong lamp-post?
It’s not about the particles.
It’s about concepts,
mechanisms, and possibilities
given our current theoretical &
experimental knowledge.
Hossenfelder, theguardian.com/commentisfree/2022/
sep/26/physics-particles-physicists

44. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Known Unknowns in Particle Physics
1990s - 2020; incomplete list
Images: Cham and Whiteson, We Have No Idea
44
Why is the Higgs boson light?
Hierarchy Problem
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
The Higgs Boson
In 2012 particle physicists announced the discovery of the Higgs boson to
great international fanfare. Almost nobody understood what the Higgs boson
was, but lots of people got very excited. The New York Times wrote that it
“represents the very best of what the process of science can offer to modern
civilization.” That’s right, the Higgs boson is apparently better than
computers, flushing toilets, and reality TV.35
So what is the Higgs boson? Here’s a quiz to test your knowledge. Take it
now and then again after you read this chapter. We hope that at the very least
your score will not decrease.
Why is there more matter than antimatter?
Why is ϴYM small? Strong CP Problem
What is the origin of neutrino mass?
Dark matter is not even in our current mathematical or physical models of the
universe. There is a large amount of stuff out there silently pulling on us, and
we don’t know what it is. We can’t possibly claim to understand our universe
without understanding this huge part of it.
Now, before you start feeling paranoid about weird, dark, mysterious
stuff floating all around you, consider this: what if dark matter is something
awesome?
Dark matter is made of something that we have no direct experience with.
It’s something we haven’t seen before, and it might behave in ways we
haven’t imagined.
Think of the amazing potential that exists here.
What if dark matter is made of some new kind of particle that we are able
to produce and harness in high-energy colliders? Or what if in discovering
what it is, we figure out something about the laws of physics we didn’t know
about before, such as a new fundamental interaction or a new way that the
existing interactions can work? And what if this new discovery lets us
manipulate regular matter in new ways?
Imagine you’ve been playing a game your whole life, and suddenly you
realize that there are special rules or special new pieces you could be playing
with. What amazing technology or understanding could be unlocked by
figuring out what dark matter is and how it works?
We can’t stay in the dark about it forever. Just because it’s dark doesn’t
mean it doesn’t matter.
What is dark matter?
Missing Mass Problem
Other puzzles (possibly related to dark matter?)
Hossenfelder, theguardian.com/commentisfree/
2022/sep/26/physics-particles-physicists
Prof. Walter Tangarife (LUC)

45. @ f l i p . t a n e d o 59
LOYOLA PHYSICS SEMINAR
Quantum Field Theory
Originally by Sue Ann Koay (USLHC, 3 Oct 2008); photo of CERN mug by Flip Tanedo (from grad school)
45
The Standard Model of Particle Physics
Lagrangian
Field: a complex function on space and time that
represents the quantum existence of a particle.

46. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Known Unknowns in Particle Physics
Images: Cham and Whiteson, We Have No Idea
46
Why is the Higgs boson light?
Hierarchy Problem
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
The Higgs Boson
In 2012 particle physicists announced the discovery of the Higgs boson to
great international fanfare. Almost nobody understood what the Higgs boson
was, but lots of people got very excited. The New York Times wrote that it
“represents the very best of what the process of science can offer to modern
civilization.” That’s right, the Higgs boson is apparently better than
computers, flushing toilets, and reality TV.35
So what is the Higgs boson? Here’s a quiz to test your knowledge. Take it
now and then again after you read this chapter. We hope that at the very least
your score will not decrease.
Why is there more matter than antimatter?
Why is ϴYM small? Strong CP Problem
What is the origin of neutrino mass?
Dark matter is not even in our current mathematical or physical models of the
universe. There is a large amount of stuff out there silently pulling on us, and
we don’t know what it is. We can’t possibly claim to understand our universe
without understanding this huge part of it.
Now, before you start feeling paranoid about weird, dark, mysterious
stuff floating all around you, consider this: what if dark matter is something
awesome?
Dark matter is made of something that we have no direct experience with.
It’s something we haven’t seen before, and it might behave in ways we
haven’t imagined.
Think of the amazing potential that exists here.
What if dark matter is made of some new kind of particle that we are able
to produce and harness in high-energy colliders? Or what if in discovering
what it is, we figure out something about the laws of physics we didn’t know
about before, such as a new fundamental interaction or a new way that the
existing interactions can work? And what if this new discovery lets us
manipulate regular matter in new ways?
Imagine you’ve been playing a game your whole life, and suddenly you
realize that there are special rules or special new pieces you could be playing
with. What amazing technology or understanding could be unlocked by
figuring out what dark matter is and how it works?
We can’t stay in the dark about it forever. Just because it’s dark doesn’t
mean it doesn’t matter.
What is dark matter?
Missing Mass Problem
Other puzzles (possibly related to dark matter?)
What is quantum
fi
eld
theory, anyway?
What is the correct way to “use"
quantum
fi
eld theory?
Does quantum gravity work?
What’s up with the strong force?
(how is the proton bound together?)
Are some of these ideas related? Can
ideas from one question help solve
other problems?
Prof. Robert McNees (LUC)
1990s - 2020; incomplete list

47. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
A great love story . . . maybe one day
47
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
Dark matter is not even in our current mathematical or physical models of the
universe. There is a large amount of stuff out there silently pulling on us, and
we don’t know what it is. We can’t possibly claim to understand our universe
without understanding this huge part of it.
Now, before you start feeling paranoid about weird, dark, mysterious
stuff floating all around you, consider this: what if dark matter is something
awesome?
Dark matter is made of something that we have no direct experience with.
It’s something we haven’t seen before, and it might behave in ways we
haven’t imagined.
Think of the amazing potential that exists here.
What if dark matter is made of some new kind of particle that we are able
to produce and harness in high-energy colliders? Or what if in discovering
what it is, we figure out something about the laws of physics we didn’t know
?
… with apologies to Andrew Grant, Science News, June 2013; cartoons: Cham and Whiteson, We Have No Idea
I never really let go of
the Higgs. Nobody is a
“dark matter theorist.”
We are theorists
studying fundamental
questions about
nature.

48. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
Outline
These pictures make sense, I promise
48
ot even in our current mathematical or physical models of the
s a large amount of stuff out there silently pulling on us, and
what it is. We can’t possibly claim to understand our universe
nding this huge part of it.
you start feeling paranoid about weird, dark, mysterious
around you, consider this: what if dark matter is something
is made of something that we have no direct experience with.
e haven’t seen before, and it might behave in ways we
d.
amazing potential that exists here.
matter is made of some new kind of particle that we are able
arness in high-energy colliders? Or what if in discovering
ure out something about the laws of physics we didn’t know
ch as a new fundamental interaction or a new way that the
ons can work? And what if this new discovery lets us
ar matter in new ways?
’ve been playing a game your whole life, and suddenly you
are special rules or special new pieces you could be playing
zing technology or understanding could be unlocked by
t dark matter is and how it works?
y in the dark about it forever. Just because it’s dark doesn’t
matter.
it mean? Who will help us in our hour of need? The answer is: the Higgs
boson.
The Higgs Boson
In 2012 particle physicists announced the discovery of the Higgs boson to
great international fanfare. Almost nobody understood what the Higgs boson
was, but lots of people got very excited. The New York Times wrote that it
“represents the very best of what the process of science can offer to modern
civilization.” That’s right, the Higgs boson is apparently better than
computers, flushing toilets, and reality TV.35
So what is the Higgs boson? Here’s a quiz to test your knowledge. Take it
now and then again after you read this chapter. We hope that at the very least
your score will not decrease.
Cham & Whiteson , We Have No Idea; Chris Burden, Urban Light, 2008, Los Angeles County Museum of Art

49. @ f l i p . t a n e d o 59
LOYOLA PHYSICS SEMINAR
Question: What’s the Difference?
Both are the Millennium Falcon from Star Wars
Images: Millenium Falcon: Wookiepedia, Lego (2017)
49

50. @ f l i p . t a n e d o 59
LOYOLA PHYSICS SEMINAR
Nature vs. Model of Nature
Images: Millenium Falcon, Lego (2017)
50
Model of nature may be enough
to diagnose puzzles in our understanding
… but do not confuse it with nature itself

51. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
51
Puzzle
Prior
data
Particle Theory

52. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
52
Prior
data
model
Particle Theory
Puzzle

53. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
53
Particle Theory
Prior
data
model
HACK
Puzzle

54. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
54
Particle Theory
Puzzle
Prior
data
NEWmodel
PREDICT
HACK

55. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
55
Particle Theory
Puzzle
Prior
data
NEWmodel
PREDICT
HACK
Interpretdatawith
respectto theory
Frameanomaliesas
features inamodel
‘Complete’ model
With newpredictions

56. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
One critical part that I left out
Physics is an experimental science
56
Hossenfelder, theguardian.com/commentisfree/
2022/sep/26/physics-particles-physicists
Cham and Whiteson, We Have No Idea
I
1.
What Is the Universe Made Of?
In Which You Learn You Are Quite Weird and
Special
f you are a human being (we’ll go with that assumption for now), then you
probably can’t help but be a little curious about the world around you. It’s
part of what it means to be human, and it’s part of why you picked up this
book.
It’s not a new feeling. Since the dawn of time, people have wondered
about the answers to some basic and very reasonable questions about the
world around us:
Prof. Rasha Abbasi
(LUC)
This…. not this.
Prof. Tareq Abuzayyad
(LUC)

57. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
How you join the effort
Theoretical scotohylology
from phdcomics.com via volkerrudolf.weebly.com/for-students.html
57
And women,
nonbinary,
& historically
excluded groups
Hossenfelder, theguardian.com/commentisfree/
2022/sep/26/physics-particles-physicists

58. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR 59
How you join the effort
Theoretical scotohylology
• Quantum
fi
eld theory
relativistic quantum mechanics: the
language of theoretical physics
• Particle Physics
know the model that you’re modifying
• General relativity & cosmology
to understand the early universe
• [ what others have missed ]
e.g. astrophysics, nuclear, condensed
matter, material science, machine learning
from phdcomics.com via volkerrudolf.weebly.com/for-students.html
58
And women,
nonbinary,
& historically
excluded groups

59. @ f l i p . t a n e d o LOYOLA PHYSICS SEMINAR
Puzzle
Prior
data
NEWmodel
PREDICT
HACK