Physics
One of the group's working tools are optical tweezers, which exploit quasimechanical properties of photons. Also, single molecules are investigated, which may generate true single photons.
Thus interest in  "What is a photon"  in the view of modern experiments came up, and on how is this photon is related to other elementary particles.   The main statements are:

i) The electron mass melectron = 511 keV/c2 can be calculated as solution of a modified Schrödinger equation, where the elementary charge is replaced by the Planck charge e / SQRT alpha. Then, the lowest energy solution is 2 * 13,6 eV (the Rydberg energy or ionization energy of the hydrogen atom) / alpha2 = 511 keV

ii) Except the proton, the masses of   a l l    other hadrons with lifetimes above 10-24 sec can be calculated as m = Z * melectron / alpha = Z * m0,  where alpha is the fine structure constant. The unprecedented accuracy is often better than 2 %, in most cases even better than 1 %.

iii) The electron mass, the proton mass, m0 of ii)  and a so far missing mass mx constitute a quadruplet of particles which can be exactly calculated solely by using the Rydberg energy, the fine structure constant alpha and ß = mproton / melectron. mx turns out to be 128,7 GeV/c2,  well in the mass range where the Higgs boson is expected.

iv) When the specific Planck charge e / (mPlanck SQRT alpha) is assigned to any mass, gravitation can be expressed as a subclass of Coulomb interaction. Then, gravitative repulsion does become possible. This may help understanding dark energy.

v) A model of the photon, which assumes that two opposite Planck charges cause its oscillations, correctly predicts that the photons energy is hv, its spin is 1 and its linear dimension is wavelength / 2pi.

vi) Bell inequalities can be violated classically. Nonlocality is not yet proven. Einstein Podolsky and Rosen are still right

vii) The fine structure constant alpha is relectron * melectron ,  the gravitation factor gamma is relectron / mproton where relectron is the classical electron radius expressed in Planck radii ,
melectron and mprotonare corresponding representations. 

In order to download the corresponding publication, click blue text below:

Particle masses, a photon model and gravitation 2011 SPIE Proc 8121.15 

A surprisingly close relationship between gravitation and electrostatic interactio 2011 Spring meeting of the Deutsche Physikalische gesellschaft Gr 12 Karlsruhe (ppt)

High accuracy calculation of the masses of  a l l  fundamental elementary particles  2010 J Mod Phys 1, 300 - 302

Single molecule experiments challenge the strict particle nature of light  2010 Int J Mol Sci 11, 304 - 311

Another loophole for the Bell inequalities    2009 Proc SPIE 7421,  1 - 7

A nonquantum mechanical explanation of the single photon double slit experiment (PDF)   2009 Proc SPIE 7421, 742104, 1 - 8

Single photons cannot be extracted from the light of multi - atom light sources (pdf) 2007 Proc SPIE 6664, 66640B 1 - 9

Expression of the dimensionless constants of nature as function of proton and electron properties 2006 Spring meeting of the Deutsche Physikalische Gesellschaft  München Gr 303 (ppt)