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, 2003-2005]:
    • Spacetime foam affects photon propagation.
    • TeV photons from active galactic nuclei ⇒   lfoam < 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 BEC-BCS crossover of ultracold gases of fermionic atoms (for example, Lithium-6 with p-wave pairing). More speculatively, there may be Fermi point splitting of the fermions of the Standard Model, which can be probed by neutrino-oscillation experiments [Klinkhamer, 2004-2006].


Neutrino-oscillation probabilities from a simple three-flavor model with both Fermi-point splittings Δb0(31) and mass-square differences Δm231. Top panels: P ≡ P(νμ → νe). Bottom panels: P'' ≡ P(νe → νμ). If CPT invariance holds, also P = P(anti-νe → anti-νμ) and P'' = P(anti-νμ → anti-νe). The probabilities are functions of the dimensionless parameters ρ ≡ (2 Eν) / (L |Δm231|) and τ ≡ L |Δb0(31)|, using natural units ℏ = c = 1 and for a neutrino beam with energy Eν and baseline L. Shown are constant–τ slices, where the heavy-solid curves in the two left panels correspond to τ = 0 (pure mass-square-difference model) and the other thin-solid, long-dashed, and short-dashed 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 high-energy end of the neutrino spectrum from Fermi-point splitting or other emergent-physics 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 |ρvac| << (EPlanck)4 ?
  • Why is ρvac ≠ 0 ?
  • Why is now ρvac ∼ ρmatter ?

Taking Lorentz-invariance 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 self-sustained Lorentz-invariant medium with a new type of conserved charge.

The argument is based solely on thermodynamics (cf. Einstein 1907) and has an analog in condensed-matter physics (Larkin-Pikin effect, 1969).

Work is in progress on the expanding (and accelerating!) universe [Klinkhamer, 2008; Klinkhamer & Volovik, 2008].

Some talks:
  1. A new approach to the cosmological constant problem (Seoul, October 2015; Update February 2018)
  2. Sphalerons and anomalies (an introduction) (Seoul, October 2015)
  3. Elementary particle physics and cosmology for engineers (and others) (Karlsruhe, February 2013)
  4. Revisiting the cosmological constant problem (Cambridge, September 2012)
  5. Superluminal neutrino: Theoretical considerations (Karlsruhe, December 2011)
  6. Cosmological constant and q-theory (Karlsruhe, March 2011)
  7. Cosmological constant problem, q-theory, and new TeV-scale physics (Toronto, September 2010)
  8. Towards a derivation of G (Bremen, July 2010)
  9. Brief introduction to q-theory and a QCD-scale modified-gravity universe (Tokyo, May 2010)
  10. Lorentz invariance, vacuum energy, and cosmology (Princeton, August 2008)
  11. UHECR bounds on Lorentz violation in the photon sector (Penn State, August 2008)
  12. Nontrivial topology and CPT violation (Uppsala, September 2006)
  13. Lorentz noninvariance and neutrino oscillations (Belgium, February/March 2006)
  14. Electroweak baryon number violation: basic mechanism (Ann Arbor, June 2003)

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