Production and Detection
of Millicharged Particles

Possible extensions of the standard model of elementary particle physics suggest the existence of particles with small, unquantized electric charge. Photon initiated pair production of millicharged fermions in an external magnetic field would manifest itself as a vacuum magnetic dichroism [hep-ph/0607118]. Laser polarization experiments searching for this effect yield, in the mass range below 0.1 eV, much stronger constraints on millicharged fermions than previously considered laboratory searches. Vacuum magnetic birefringence originating from virtual pair production gives a slightly better constraint for masses between 0.1 eV and a few eV. Possibly, the vacuum magnetic dichroism observed by PVLAS arises from pair production of such millicharged fermions rather than from single production of axion-like particles. Such a scenario can be confirmed or firmly excluded by a search for invisible decays of orthopositronium with a sensitivity of about 10^{-9} in the corresponding branching fraction.

In [hep-ph/0608238], we have investigated Schwinger pair production of millicharged fermions in the strong electric field of cavities used for particle accelerators. Even without a direct detection mechanism at hand, millicharged particles, if they exist, contribute to the energy loss of the cavity and thus leave an imprint on the cavity's quality factor. Already conservative estimates substantially constrain the electric charge of these hypothetical particles; the resulting bounds are competitive with the currently best laboratory bounds which arise from experiments based on polarized laser light propagating in a magnetic field. We have proposed an experimental setup for measuring the electric current comprised of the millicharged particles produced in the cavity.

Such millicharges arise generically from kinetic-mixing in theories containing at least two U(1) gauge factors. In [hep-ph/0608248], we have pointed out that the required multiple U(1) factors, the size of kinetic-mixing, and suitable matter representations to explain the PVLAS data occur very naturally in the context of realistic extensions of the Standard Model (SM) of elementary particle physics based on string theory.

Publications:

• P. Arias, D. Cadamuro, M. Goodsell, J. Jaeckel, J. Redondo, A. Ringwald,
  WISPy Cold Dark Matter,
  arXiv:1201.5902 [hep-ph]

• M. Goodsell, S. Ramos-Sanchez, A. Ringwald,
  Kinetic Mixing of U(1)s in Heterotic Orbifolds,
  arXiv:1110.6901 [hep-th], JHEP 1201 (2012) 021

• O. Baker, M. Betz, F. Caspers, J. Jaeckel, A. Lindner, A. Ringwald, Y. Semertzidis, P. Sikivie, K. Zioutas,
  Prospects for Searching Axion-like Particle Dark Matter with Dipole, Toroidal and Wiggler Magnets,
  arXiv:1110.2180 [physics.ins-det]

• S. Andreas, M.D. Goodsell, A. Ringwald,
  Dark matter and Dark Forces from a supersymmetric hidden sector,
  arXiv:1109.2869 [hep-ph]

• M. Cicoli, M. Goodsell, J. Jaeckel, A. Ringwald,
  Testing String Vacua in the Lab: From a Hidden CMB to Dark Forces in Flux Compactifications,
  arXiv:1103.3705 [hep-th], JHEP 1107 (2011) 114

• P. Arias, J. Jaeckel, J. Redondo, A. Ringwald,
  Optimizing Light-Shining-through-a-Wall Experiments for Axion and other WISP Searches,
  arXiv:1009.4875 [hep-ph], Phys. Rev. D82 (2010) 115018

• K. Ehret et al. [ALPS Collaboration],
  New ALPS Results on Hidden-Sector Lightweights,
  arXiv:1004.1313 [hep-ex], Phys. Lett. B689 (2010) 149

• J. Jaeckel, A. Ringwald,
  The Low-Energy Frontier of Particle Physics,
  arXiv:1002.0329 [hep-ph], Ann. Rev. Nucl. Part. Sci. 60 (2010) 405

• C. Burrage, J. Jaeckel, J. Redondo, A. Ringwald,
  Late time CMB isotropies constrain mini-charged particles,
  arXiv:0909.0649 [astro-ph.CO], JCAP 0911 (2009) 002

• M. Goodsell, J. Jaeckel, J. Redondo, A. Ringwald,
  Naturally Light Hidden Photons in LARGE Volume String Compactifications,
  arXiv:0909.0515 [hep-ph], JHEP 0911 (2009) 027

• F. Caspers, J. Jaeckel, A. Ringwald,
  Feasibility, engineering aspects and physics reach of microwave cavity experiments searching for hidden photons and axions,
  arXiv:0908.0759 [hep-ex], JINST 4 (2009) P11013

• K. Ehret, M. Frede, S. Ghazaryan, M. Hildebrandt, E.-A. Knabbe, D. Kracht, A. Lindner, J. List, T. Meier, N. Meyer, D. Notz, J. Redondo, A. Ringwald, G. Wiedemann, B. Willke [ALPS Collaboration],
  Resonant laser power build-up in ALPS - a "light-shining-through-walls" experiment -,
  arXiv:0905.4159 [hep-ex], Nucl. Instrum. Meth. A 612 (2009) 83

• J. Jaeckel, J. Redondo, A. Ringwald,,
  Hidden Laser Communications Through Matter - An application of meV-scale hidden photons,
  arXiv:0903.5300 [hep-ph], Europhys. Lett. 87 (2009) 10010

• M. Ahlers, J. Jaeckel, A. Ringwald,,
  The Discovery Potential of Laser Polarization Experiments,
  arXiv:0812.3150 [hep-ph], Phys. Rev. D 79 (2009) 075017

• M. Ahlers, J. Jaeckel, J. Redondo, A. Ringwald,,
  Probing Hidden Sector Photons through the Higgs Window,
  arXiv:0807.4143 [hep-ph], Phys. Rev. D 78 (2008) 075005

• J. Jaeckel, J. Redondo, A. Ringwald,,
  Signatures of a hidden cosmic microwave background,
  arXiv:0804.4157 [astro-ph], Phys. Rev. Lett. 101 (2008) 131801

• S.A. Abel, M.D. Goodsell, J. Jaeckel, V.V. Khoze, A. Ringwald,
  Kinetic Mixing of the Photon with Hidden U(1)s in String Phenomenology,
  arXiv:0803.1449 [hep-ph], JHEP 0807 (2008) 124

• M. Ahlers, H. Gies, J. Jaeckel, J. Redondo, A. Ringwald,,
  Laser experiments explore the hidden sector,
  arXiv:0711.4991 [hep-ph], Phys. Rev. D 77 (2008) 095001

• A. Lindner, A. Ringwald,,
  The low-energy frontier,
  Phys. World 20N8 (2007) 32

• J. Jaeckel, A. Ringwald,,
  A Cavity Experiment to Search for Hidden Sector Photons,
  arXiv:0707.2063 [hep-ph], Phys. Lett. B659 (2008) 509

• M. Ahlers, H. Gies, J. Jaeckel, J. Redondo, A. Ringwald,,
  Light from the Hidden Sector,
  arXiv:0706.2836 [hep-ph], Phys. Rev. D 76 (2007) 115005

• M. Ahlers, H. Gies, J. Jaeckel, A. Ringwald,
  On the Particle Interpretation of the PVLAS Data: Neutral versus Charged Particles,
  hep-ph/0612098, Phys. Rev. D75 (2007) 035011

• Steven A. Abel, Joerg Jaeckel, Valentin V. Khoze, Andreas Ringwald,
  Illuminating the Hidden Sector of String Theory by Shining Light through a Magnetic Field,
  hep-ph/0608248, Phys. Lett. B666 (2008) 66

• H. Gies, J. Jaeckel, A. Ringwald,
  Accelerator Cavities as a Probe of Millicharged Particles,
  hep-ph/0608238, Europhys. Lett. 76 (2006) 794

• H. Gies, J. Jaeckel, A. Ringwald,
  Polarized Light Propagating in a Magnetic Field as a Probe of Millicharged Fermions,
  hep-ph/0607118, Phys. Rev. Lett. 97 (2006) 140402

Reviews:

• M. Schwarz, A. Lindner, J. Redondo, A. Ringwald, G. Wiedemann,
  Solar Hidden Photon Search,
  Proc. 7th Patras Workshop on Axions, WIMPs and WISPs, 27 June - 1 July 2011, Mykonos, Greece
  arXiv:1111.5797 [astro-ph.IM].

• P. Arias, A. Ringwald,
  Illuminating WISPs with photons,
  Proc. PHOTON2011, 22-27 May 2011, Spa, Belgium
  arXiv:1110.2126 [hep-ph].

• J. Redondo, A. Ringwald,
  Light shining through walls,
  arXiv:1011.3741 [hep-ph], Contemp. Phys. 52 (2011) 211

• P. Arias, J. Jaeckel, J. Redondo, A. Ringwald,
  Improving the Discovery Potential of Future Light-Shining-through-a-Wall Experiments,
  Proc. 6th Patras Workshop on Axions, WIMPs and WISPs, 5-9 July 2010, Zurich University, Switzerland
  arXiv:1009.1519 [hep-ph].

• S. Andreas, A. Ringwald,
  Status of sub-GeV Hidden Particle Searches,
  Proc. 6th Patras Workshop on Axions, WIMPs and WISPs, 5-9 July 2010, Zurich University, Switzerland
  arXiv:1008.4519 [hep-ph].

• A. Ringwald,
  Challenges and Opportunities for the Next Generation of Photon Regeneration Experiments,
  Proc. Axions 2010, January 15-17, 2010, Gainesville, Florida
  arXiv:1003.2339 [hep-ph].

• M. Goodsell, A. Ringwald,
  Light hidden-sector U(1)s in string compactifications,
  Proc. 9th Hellenic School on Elementary Particle Physics and Gravity, Corfu 2009, Corfu, Greece
  arXiv:1002.1840 [hep-th], Fortschr. Phys. 58 (2010) 716

• A. Ringwald,
  From Axions to Other WISPs,
  Proc. 4th Patras Workshop on Axions, WIMPs and WISPs, June 18-21, 2008, Hamburg, Germany
  arXiv:0810.3106 [hep-th].

• R. Battesti et al.,,
  Axion Searches in the Past, at Present, and in the Near Future,
  arXiv:0705.0615 [hep-ex]

• A. Ringwald,
  Particle Intepretations of the PVLAS Data,
  Proc. XII International Workshop on ``Neutrino Telescopes, March 6-9, 2007, Venice, Italy
  arXiv:0704.3195 [hep-ph].

• A. Ringwald,
  Photon Regeneration Plans,
  Proc. 6th International Workshop on the Identification of Dark Matter (IDM 2006), Island of Rhodes, Greece, 11--16th September, 2006
  hep-ph/0612127.

Recent Talks:

• Physics Case for WISP Searches with Intense Photon- and Electron-Beams,
  Trieste/I, May 2011 (48 pages).

• Weakly Interacting Slim Particles and New Experiments at the Intensity Frontier,
  Bad Honnef/D, March 2011 (55 pages).

• Hidden Photons in String Theory, in Cosmology, and in the Laboratory,
  Hamburg/D, February 2011 (27 pages).

• Physics Case for Hidden Photon Searches with ALPS, SHIPS, and HIPS,
  Hamburg/D, February 2011 (32 pages).

• Searching for ALPs and Hidden Photons with Intense Photon- and Electron-Beams,
  Dresden/D, January 2011 (40 pages).

• Searching for ALPs and other WISPs at the intensity frontier,
  Villigen/CH, December 2010 (41 pages).

• Searching for sub-GeV scale hidden-sector particles exploiting DESY's electron beams,
  Hamburg/D, November 2010 (13 pages).

• Sub-GeV Scale Dark Forces?!,
  Mainz/D, November 2010 (32 pages).

• New Experiments at the Intensity Frontier,
  Dortmund/D, October 2010 (18 pages).

• Ultra-Light Particles Beyond the Standard Model,
  Bad Honnef/D, October 2010 (42 pages).

• Attacking Dark Forces with Intense Electron Beams at DESY,
  Hamburg/D, March 2010 (33 pages).

• Dark Forces Attack at DESY,
  Hamburg/D, January 2010 (32 pages).

• Challenges and Opportunities for the Next-Generation of Photon Regeneration Experiments,
  Gainesville/USA, January 2010 (17 pages).

• Attacking Hidden Forces with Intense Photon- and Electron-Beams,
  Valparaiso/Chile, January 2010 (42 pages).

• Dark Forces Attack,
  Bonn/D, December 2009 (29 pages).

• Light hidden U(1)s in LARGE volume string compactifications,
  SLAC/USA, September 2009 (28 pages).

• Theory and phenomenology of hidden U(1)s from string compactifications,
  Corfu/GR, September 2009 (27 pages).

• Suche nach versteckten Teilchen,
  Heiligenstedten/D, June 2009 (28 pages).

• Shedding Light on the Hidden Sector - Particle Physics with Low-Energy Photons,
  Zeuthen/D, June 2009 (50 pages).

• Are There Ultralight Particles in the Hidden Sector? - Particle Physics with Low-Energy Photons,
  Geneva/CH, June 2009 (56 pages).

• Is There New Physics at the Milliscale? - Particle Physics with Low-Energy Photons,
  Heidelberg/D, May 2009 (57 pages).

• Kinetic mixing of hidden U(1)s with the visible U(1) in string compactifications,
  Bonn/D, April 2009 (26 pages).

• Einblick in versteckte Welten - Teilchenphysik mit niederenergetischen Photonen,
  Jena/D, January 2009 (41 pages).

PR:

• Hamburger Wissenschaftler suchen Versteckte Photonen,
  Hamburger Abendblatt, Dec 13, 2011.

• 'Light shining through walls' experiment gets a boost,
  LaserFocusWorld, Aug 01, 2009.

• `Hidden Photons' to send secret emails through Earth,
  NewScientist, April 25, 2009.

• Vergebliche Suche nach Axion-artigen Teilchen,
  NZZ, November 28, 2007.

• Results question merit of axion experiments,
  by Jon Cartwright,
  physicsworld, headline news, November 21, 2007.

• Fundamental physics re-explored in Patras,
  CERN COURIER, Faces and Places, November 20, 2007.

• Mit Laserlicht durch die Wand,
  NZZ, July 25, 2007.

• Mit dem Ersatzteil auf Teilchenjagd,
  by Christof Rührmair,
  DIE ZEIT, Nr. 23, May 31, 2007, p. 46.

• War das da eben vielleicht ein Axion?,
  by Ulf von Rauchhaupt,
  Frankfurter Allgemeine Sonntagszeitung, February 18, 2007, p. 64.

• Axion stations,
  The Economist, December 23, 2006.

• Laser could create dark-matter particles,
  by Edwin Cartlidge, News Editor of Physics World,
  PhysicsWeb July 2006.

• Let there be axions,
  by Konstantin Zioutas,
  CERN Courier July/August 2006, pp. 19-22.

• The first axion?,
  by Steve Lamoreaux,
  Nature 44 (2006) 31, May 4, 2006.

• Accidence and substance,
  The Economist, April 6, 2006.

• Magnet Experiment Appears to Drain Life From Stars,
  by Michael Schirber,
  Science 311 (2006) 1535.