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Gravity and Particle Physics at Different
Scales
by
Gia Dvali :
Brief review of Max-Planck-Institute for Physics
Cosmology/Astro-Particle & Beyond the Standard Model physics research.
Physics at 10-17 cm:
Understanding fundamental physics behind the
stability of weak interaction scale:
Role of gravity;
Supersymmetric Higgs as a pseudo-Goldstone boson
(sound-wave);
What is the connection between gravity and
particle species?
Species = Geometry?
Implications for LHC: Micro black holes; String
Resonances; Extra Dimensions; …
Fundamental Physics at 1028 cm:
What is the reason behind the accelerated expansion
of the Universe?
Self-acceleration? Is graviton truly massless?
Is it even consistent to change gravity at large distances?
Why can’t extra dimensions manifest themselves at large
as opposed to small distances?
What are the observational consequences of this
approach?
Is the vacuum energy de-gravitated because of graviton
mass?
Physics in very early Universe:
Inflation in String Theory:
Brane Inflation?
Big-Bang from annihilating D-branes?
Understanding String Theoretic cosmology in terms
of effective field theory:
Brane inflation = Supersymmetric D-term inflation
Cosmic Strings as fundamental superstrings?
THE SEARCHES OF THE NEW (BEYOND THE STANDARD
MODEL) PHYSICS AT THE LARGE HADRON COLLIDER
ARE (Mainly) MOTIVATED BY THE HIERARCHY PROBLEM,
AN INEXPLICABLE STABILITY OF THE WEAK INTERACTION
SCALE (MW = 102 GeV) VERSUS THE PLANCK MASS
(MP = 1019 GeV),
WHY IS M2W/M2P = 10-34 ?
THE HIERARCHY PROBLEM IS NOT ABOUT BIG/SMALL NUMBERS!
THERE ARE PLENTY OF BIG/SMALL NUMBERS IN NATURE THAT
ARE OF NO MYSTERY.
12
10
ELEPHANTS (OR HUMANS) ARE BIG, BECAUSE
THEY CARRY A HUGE BARYON NUMBER.
THE HIERARCHY PROBLEM IS ABOUT THE UV
STABILITY OF THE VERY SMALL NUMBER
M2W/M2P = 10-34
STANADARD MODEL
GAUGE FORCES:
SU(3)xSU(2)xU(1)
MATTER:
QUARKS : (u,d) (c,s) (t,b),
HIGGS:
LEPTONS: (e,νe) (μ, νμ) (τ, ντ)
H
The weak scale is set by the vacuum expectation value of the Higgs
field, which is related to the mass of the Higgs boson,
This mass is UV-unstable!
mH .
UV-instability of the Higgs mass
H
t
H
H
+
+
t
H
H
δm2H ≈ Λ2 !
The natural cutoff is the gravity scale Λ = MP
Without gravity one could have said that the problem
is not so severe: After all, the theory must have a scale and it
happens to be around 100GeV.
But with gravity there is a very little flexibility.
In Einstein’s gravity MP is the scale where gravitational
interactions of elementary particles become strong.
In any sensible theory of gravity, which at large distances
reduces to Einstein’s GR, a point-like elementary particle
heavier than MP makes no sense.
In fact we know very well what such an object is:
Because its gravitational Schwarzschild radius exceeds its
Compton wavelength,
R = m/M2P > 1/m ,
R
it is a macroscopic classical black hole!
And becomes more and more classical with the growing
mass.
Without gravity the problem could have been less severe, but with
gravity there is no way out:
The particles running in the loop cannot have arbitrarily
high energies without becoming big black holes!
H
H
’98 Quantum Gravity at TeV Idea:
Weak scale is stable, because the quantum gravity
scale M* ≈ TeV !
(Arkani-Hamed, Dimopoulos, GD;
Antoniadis, Arkani-Hamed, Dimopoulos, GD)
But, if gravity becomes strong around the TeV scale, why is
the large distance gravity so much weaker than all the other
forces of nature?
For example, gravitational attraction between the two protons at 1 m
distance is 1037 times weaker of their Coulomb repulsion!
Original Realization: Extra Dimensions
As a result of the dilution, there is a simple
relation between the true quantum gravity scale
and the Planck mass measured at large distances:
M2P = M2* (M*R)n
Volume of extra space
The Role of Particle Species in Lowering Gravity Scale.
M2P = M2* (M*R)n
Volume of extra space
We can now understand the geometric relations in terms of particle
species number counting,
M2P = M2* N,
Where N is the number of species . This very important, because
the latter expression turns out to be more general than the former:
What matters is the number of species!
Hawking flux of N species with T = 1/R
The black holes of size
R < L* = √N / MP
cannot afford to be semi-classical, because they half-evaporate
Faster than their size!
Equivalently, the rate of temperature-change is faster than the
temperature-squared
dT/dt > T2
Thus, the fundamental length scale below which
no semi-classical black holes can exist in any
consistent theory with N species is
L* = √N / MP
and the corresponding mass scale marks the cutoff.
M2* = M2P /N
Message encoded in a green flavor
Pixel of size L, with all
the sample flavors
Strength of Gravity as Function of Distance
mrg
M-1P
√N/MP
R
m-1
The black hole arguments show, that the class of theories
which solve the Hierarchy Problem by TeV quantum gravity
scale, is much larger.
In particular, any theory with N = 1032 particle species, will do
this.
The role of these 1032 species, can equally well be played by
1032 Kaluza-Klein gravitons from large extra dimensions, or by
1032 copies of the Standard Model!
Einsteinian Black Holes carry no hair
Such Black Holes can only be distinguished by exactly conserved quantum
numbers measurable at infinity.
For example, such numbers are the mass of a Black Hole and its electric
charge.
On the other hand, quark and lepton flavors in the Standard Model are not
exactly-conserved quantum numbers of nature, and are impossible to
measure outside the Black Hole horizon.
Flavor -violation by Black Holes can be visualized by the following
thought experiment.
In Standard Model we can produce a large classical black hole by colliding
particles of a given flavor , e.g., electron-positron. If the Hawking
Temperature of this Black Hole is sufficiently high, it will evaporate in all three
lepton generations (and in other possible species) fully democratically,
τ+
e+ + e-
μEverything possible
e+
e-
Thus, macroscopic Black Holes violate flavor maximally.
What about the microscopic Black Holes
that may be produced at LHC?
It turns out that story for them is different:
The small black holes must carry memory
about their origin, and are non-democratic!
In particular, for center of mass energies
E > Mdb = M* (M*R db )n+1 ,
d-b transition processes become order one.
d
s
b
d
The number of quanta emitted Nfinal = (E/M* )(n+2)/(n+1)
Hawking flux of species in string theory
GD & Lüst ;
GD & Gomez
Naively there are exponentially growing number of species, so
that the black holes smaller than
R < LS
cannot afford to be semi-classical.
But, this is not true. The effective number of species to which
black holes evaporate turns out to be bounded by:
2
NEFF = 1/gS !
Experimental signatures of low scale quantum gravity are
pretty spectacular.
These include formation of mini black holes, Kaluza-Klein
gravitons, and string vibrations in particle collisions
(e.g., high spin recurrences of ordinary particles).
(For a recent detailed study of string production within type
II strings see work by, Lust, Stieberger, Taylor; ... )
Gravitational shortcut
STRING THEORY PICTURE
open
strings
ordinary
particles
closed
strings
gravity
This is an exciting time for the particle physics community.
LHC will directly probe the mechanism which is
responsible for generating the weak interaction scale and
masses of the elementary particles.
And, there is a strong theoretical indication, that LHC will
also probe physics that is behind the stability of the above
scale.
If the ideas presented in this talk have anything to do with
nature, LHC has an exceptional chance of experimentally
discovering and studying the nature of quantum gravity.
Universe’s acceleration:
Hubble parameter:
Friedmann equation (flat universe)
Dark energy or Modified Gravity?
Large distance modification of gravity at the fundamental level
Implies that graviton is not exactly massless.
Equivalently, in geometric terms this can be understood as
extra dimensions showing-up at cosmological distances, so that
gravitational flux spreads out Into the extra space.
This spread-out from observational point of view would
manifest itself as:
1) Change of expansion law, that can be tested by cosmological
observations;
2) As anomalous correction to planetary motions; For example
Anomalous precession of the lunar orbit =1.4 x 10 -12
3) As observable modification to the spectrum of density
perturbations.
FRW Equation is modified
H2 - H/rc = 
Early cosmology in normal H>>rc-1
Late cosmology
H  H = rc-1
At late times Universe is self-accelerating!
NO NEED IN DARK ENERGY?
LUNAR RANGING TEST OF MODIFIED GRAVITY
Predicted anomalous perihelion precession of the
lunar orbit
=1.4 x 10 -12
Todays accuracy:
=2.4 x 10 -11
10-fold improvement is expected
Max Planck Research Group:
Beyond the Standard Model
Members:
• Group leader: Stefan Antusch
• Postdocs:
– Lorenzo Calibbi
– Yu Min Kim
– Toshihiko Ota
– Enrique Fernandez-Martinez
(since 10/10 → CERN)
– Koushik Dutta
(since 10/10 → DESY)
Group started 9/2007
• Phd students:
– Jochen Baumann
– Sebastian Halter
– Philipp Kostka
– Martin Spinrath
(since 10/10 → SISSA)
• Diploma students:
– Valerie Domcke
– Vinzenz Maurer
Max Planck Research Group:
Beyond the Standard Model
Research:
Neutrino
Physics
Origin of neutrino mass?
Origin of large lepton mixing?
(Non-)unitarity of UPMNS?
Unified
Theories
& Flavour
Physics
Unification of forces?
Origin of flavour structure?
Flavour in supersymmetry?
Early Universe
Cosmology
Inflation in particle physics theories?
Matter-antimatter asymmetry?
Dark matter? Origin of structure?
Max Planck Research Group:
Beyond the Standard Model
Selected Scientific Highlights:
•
Neutrino Physics:
Theory and bounds for non-unitary lepton mixing matrix UPMNS
Bounds on gauge invariant new interactions in the lepton sector
•
Unified Theories & Flavour Physics:
Predictive flavour structure (SM+SUSY) from family symmetries
New GUT predictions for quark and lepton mass ratios → Poster
•
Early Universe Cosmology:
New inflaton candidate: Unified matter superparticle in SUSY GUTs
New models of inflation in supergravity (e.g. with Heisenberg symmetry)
→ Poster
•
Astroparticle Theory
Beyond the Standard Model
Cosmology
Senior staff
Recent departures
Georg Raffelt
Carla Biggio  U Barcelona
Frank Steffen (also IMPRS coordinator) Basudeb Dasgupta  Ohio State
Leo Stodolsky (director emeritus)
Josef Pradler  Perimeter
Alessandro Mirizzi
Postdocs & Fellows
 Junior Prof. U Hamburg
Mattias Blennow (Marie Curie fellow)
Yvonne Y.Y. Wong
Javier Redondo
 Junior Prof. RWTH Aachen
Shun Zhou (AvH fellow)
Pasquale Di Bari
Christoph Weniger
 Lecturer, Southampton
Ph.D. Students
Davide Cadamuro
Recent exchange students
Peter Graf
Irene Tamborra (U Bari, Italy)
Jonas Lindert
Tina Lund (U Aarhus, Denmark)
David de Sousa Seixas
Amol Patwardhan (Mumbai, India)
Strong synergy with Stefan Antusch’s Independent MPG Junior Research Group
(Collaborative projects & common Thursday seminar)
Networking & Collaborations
Transregional Collaborative Research Centre TR 27
Neutrinos and Beyond
Weakly Interacting Particles in Physics, Astrophysics & Cosmology
TUM, MPP, MPA, KIT (Karlsruhe), U Tübingen, MPIK (Heidelberg)
Origin and Structure of the Universe
The Cluster of Excellence for Fundamental Physics
TUM, LMU, MPP, MPA, MPE, ESO
Max Planck India Partnergroup (until 12/2009)
Neutrino Physics and Astrophysics
Amol Dighe (MPP alumnus) and his group at
Tata Institute of Fundamental Research (TIFR), Bombay, India
International School on AstroParticle Physics (30+ Institutes)
U Bari, Ferrara, Genova, Milano, Milano Bicocca, Napoli, Padova, Roma Vergata,
Torino & LNGS, TUM, MPP, U Heidelberg, MPIK, U & FZ Karlsruhe, APC & Orsay,
Weizmann, U Aarhus, Trondheim, Stockholm, INR & Kurchatov, U Valencia,
Santiago de Compostela, Autonoma Madrid, …
CAST
Experiment
Astroparticle
Physics
Research Topics
Dark matter particles (WIMP-like & SUSY)
- Early-universe production
- Collider signatures, BBN impact
- Detection (indirect & CRESST)
Frank Steffen
Christoph Weniger
Mattias Blennow
Leo Stodolsky
Axions and similar particles
- Experimental searches (CAST, ALPS)
- Photon conversion in lab & astro B fields
- Primordial production, cosmo limits
Javier Redondo
Georg Raffelt
Frank Steffen, students
(A.Mirizzi until 2009)
Neutrinos & axions in cosmology
- Mass limits from precision data
- Extra radiation, flavor oscillations, BBN
- Leptogenesis
Georg Raffelt
(previously Di Bari, Wong)
Students
Supernova neutrinos
- Collective flavor oscillations
- Experimental signatures from next SN
- Sterile neutrino production
Georg Raffelt, Shun Zhou
(B. Dasgupta, A. Mirizzi
until 2009/10)
Students
Neutrino phenomenology & BSM
- Experimental signatures at LBL expts
- MonteCubes software
- Models, non-standard interactions
Mattias Blennow
Shun Zhou
(Carla Biggio until 2010)
with Antusch group