Focus: fundamental aspects of elementary particle physics
and structure of spacetime

Four main topics:

1. Baryon number violation
through nonperturbative effects in
the Electroweak Standard Model:

Sphalerons and spectral flow:
New results on spectral flow and sphalerons have been obtained
[Klinkhamer & Lee, 2001], [Klinkhamer & Rupp, 2005]
and are currently under investigation.
For two reviews, see
[Klinkhamer, 2002], [Klinkhamer & Rupp, 2003].

2. CPT anomaly:

Chiral gauge theories defined over a topologically
nontrivial space manifold have an anomalous breaking of
Lorentz and CPT invariance. A recent review:
[Klinkhamer, 2005]





Microscopic structure of spacetime [Klinkhamer & Rupp, 20032005]:
 Spacetime foam affects photon propagation.
 TeV photons from active galactic nuclei
⇒ l_{foam} < 1.6 × 10^{22} cm.

3. Quantum phase transition and neutrino oscillations:

A new type of quantum phase transition due to Fermi point splitting has been proposed [Klinkhamer & Volovik, 2004].
Such a quantum critical point may appear in the BECBCS crossover of ultracold gases of fermionic atoms (for example, Lithium6 with pwave pairing).
More speculatively, there may be Fermi point splitting of the fermions of the Standard Model, which can be probed by neutrinooscillation experiments [Klinkhamer, 20042006].



Neutrinooscillation probabilities
from a simple threeflavor model with both
Fermipoint splittings Δb_{0}^{(31)}
and masssquare differences Δm^{2}_{31}.
Top panels: P ≡ P(ν_{μ} → ν_{e}).
Bottom panels: P'' ≡ P(ν_{e} → ν_{μ}).
If CPT invariance holds, also P = P(antiν_{e} →
antiν_{μ}) and
P'' = P(antiν_{μ} → antiν_{e}).
The probabilities are functions of the dimensionless parameters
ρ ≡ (2 E_{ν}) / (L Δm^{2}_{31}) and
τ ≡ L Δb_{0}^{(31)},
using natural units ℏ = c = 1 and
for a neutrino beam with
energy E_{ν} and baseline L.
Shown are constant–τ slices, where the heavysolid curves
in the two left panels correspond to τ = 0
(pure masssquaredifference model)
and the other thinsolid, longdashed, and shortdashed curves for
positive τ
correspond to τ = 1,2,0 (mod 3), respectively.
These results show that there could be strong T–violating
(and CP–violating) effects at the highenergy end of
the neutrino spectrum from Fermipoint splitting
or other emergentphysics dynamics.


4. Vacuum energy and cosmology:

Since 1998, it has become clear that there is not one cosmological constant problem
but that there are three:


Why is ρ_{vac} << (E_{Planck})^{4} ?

Why is ρ_{vac} ≠ 0 ?

Why is now ρ_{vac} ∼ ρ_{matter} ?

Taking Lorentzinvariance seriously (cf. recent UHECR bounds on Lorentz
violation in the photon sector [Klinkhamer, 2008]), a new approach [Klinkhamer & Volovik, 2008] to this set of
problems is based on the following assumption:
the perfect quantum vacuum can be considered to behave as a selfsustained
Lorentzinvariant medium with a new type of conserved charge.
The argument is based solely on thermodynamics (cf. Einstein 1907) and has
an analog in condensedmatter physics (LarkinPikin effect, 1969).
Work is in progress on the expanding (and accelerating!) universe
[Klinkhamer, 2008;
Klinkhamer & Volovik, 2008].

Some talks:

 A new approach to the cosmological constant problem (Seoul, October 2015; Update February 2018)
 Sphalerons and anomalies (an introduction) (Seoul, October 2015)
 Elementary particle physics and cosmology for engineers (and others) (Karlsruhe, February 2013)
 Revisiting the cosmological constant problem (Cambridge, September 2012)
 Superluminal neutrino: Theoretical considerations (Karlsruhe, December 2011)
 Cosmological constant and qtheory (Karlsruhe, March 2011)
 Cosmological constant problem, qtheory, and new TeVscale physics (Toronto, September 2010)
 Towards a derivation of G (Bremen, July 2010)
 Brief introduction to qtheory and a QCDscale modifiedgravity universe (Tokyo, May 2010)
 Lorentz invariance, vacuum energy, and cosmology (Princeton, August 2008)
 UHECR bounds on Lorentz violation in the photon sector (Penn State, August 2008)
 Nontrivial topology and CPT violation (Uppsala, September 2006)
 Lorentz noninvariance and neutrino oscillations (Belgium, February/March 2006)
 Electroweak baryon number violation: basic mechanism (Ann Arbor, June 2003)
