Joerg Jaeckel

The Low-Energy Frontier of Particle Physics

Most embeddings of the Standard Model into a more unified theory, in particular those based on supergravity or superstrings, predict the existence of a hidden sector of particles that have only very weak interactions with visible-sector Standard Model particles. Some of these exotic particle candidates [for instance, axions, axion-like particles, and hidden U(1) gauge bosons] may be very light, with masses in the subelectronvolt range, and may have very weak interactions with photons. Correspondingly, these very weakly interacting subelectronvolt particles (WISPs) may lead to observable effects in experiments (as well as in astrophysical and cosmological observations) searching for light shining through a wall, for changes in laser polarization, for nonlinear processes in large electromagnetic fields, and for deviations from Coulombs law. We present the physics case and a status report of this emerging low-energy frontier of fundamental physics.

Kinetic Mixing of the Photon with Hidden U(1)s in String Phenomenology

Embeddings of the standard model in type II string theory typically contain a variety of U(1) gauge factors arising from D-branes in the bulk. In general, there is no reason why only one of these - the one corresponding to weak hypercharge - should be massless. Observations require that standard model particles must be neutral (or have an extremely small charge) under additional massless U(1)s, i.e. the latter have to belong to a so called hidden sector. The exchange of heavy messengers, however, can lead to a kinetic mixing between the hypercharge and the hidden-sector U(1)s, that is testable with near future experiments. This provides a powerful probe of the hidden sectors and, as a consequence, of the string theory realisation itself. In the present paper, we show, using a variety of methods, how the kinetic mixing can be derived from the underlying type II string compactification, involving supersymmetric and nonsupersymmetric configurations of D-branes, both in large volumes and in warped backgrounds with fluxes. We first demonstrate by explicit example that kinetic mixing occurs in a completely supersymmetric set-up where we can use conformal field theory techniques. We then develop a supergravity approach which allows us to examine the phenomenon in more general backgrounds, where we find that kinetic mixing is natural in the context of flux compactifications. We discuss the phenomenological consequences for experiments at the low-energy frontier, searching for signatures of light, sub-electronvolt or even massless hidden-sector U(1) gauge bosons and minicharged particles.

A facility to search for hidden particles at the CERN SPS: the SHiP physics case.

This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, [Formula: see text] and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the standard model and describe interactions between new particles and four different portals-scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the standard model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation.

WISPy Cold Dark Matter

Very weakly interacting slim particles (WISPs), such as axion-like particles (ALPs) or hidden photons (HPs), may be non-thermally produced via the misalignment mechanism in the early universe and survive as a cold dark matter population until today. We nd that, both for ALPs and HPs whose dominant interactions with the standard model arise from couplings to photons, a huge region in the parameter spaces spanned by photon coupling and ALP or HP mass can give rise to the observed cold dark matter. Remarkably, a large region of this parameter space coincides with that predicted in well motivated models of fundamental physics. A wide range of experimental searches { exploiting haloscopes (direct dark matter searches exploiting microwave cavities), helioscopes (searches for solar ALPs or HPs), or light-shining-through-a-wall techniques { can probe large parts of this parameter space in the foreseeable future.

Laser experiments explore the hidden sector

Recently, the laser experiments BMV and GammeV, searching for light shining through walls, have published data and calculated new limits on the allowed masses and couplings for axionlike particles. In this paper we point out that these experiments can serve to constrain a much wider variety of hidden-sector particles such as, e.g., minicharged particles and hidden-sector photons. The new experiments improve the existing bounds from the older BFRT experiment by a factor of 2. Moreover, we use the new PVLAS constraints on a possible rotation and ellipticity of light after it has passed through a strong magnetic field to constrain pure minicharged particle models. For masses

Dynamical breaking of U(1)(R) and supersymmetry in a metastable vacuum

\ensuremath{\lesssim}0.05\text{ }\text{ }\mathrm{eV}

SUSY breaking by a metastable ground state: why the early Universe preferred the non-supersymmetric vacuum

, the charge is now restricted to be less than

Emergence of the electroweak scale through the Higgs portal

(3\ensuremath{-}4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}

Light from the hidden sector: Experimental signatures of paraphotons

times the electron electric charge. This is the best laboratory bound and comparable to bounds inferred from the energy spectrum of the cosmic microwave background.

Polarized Light Propagating in a Magnetic Field as a Probe for Millicharged Fermions

Abstract We consider the metastable N = 1 QCD model of Intriligator, Seiberg and Shih (ISS), deformed by adding a baryon term to the superpotential. This simple deformation causes the spontaneous breaking of the approximate R -symmetry of the metastable vacuum. We then gauge the flavour SU ( 5 ) f and identify it with the parent gauge symmetry of the Standard Model (SM). This implements direct mediation of supersymmetry breaking without the need for an additional messenger sector. A reasonable choice of parameters leads to gaugino masses of the right order. Finally, we speculate that the entire “ISS × SM” model should be interpreted as a magnetic dual of an (unknown) asymptotically free theory.