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We analyze the data from two recent experiments designed to search for solar axions within the context of multidimensional theories of the Kaluza-Klein type. In these experiments, axions were supposed to be emitted from the solar core, in M1 transitions between the first excited state and the ground state of 57Fe and 7Li. Because of the high multiplicity of axionic Kaluza-Klein states which couple with the strength of ordinary QCD axions, we obtain much more stringent experimental limits on the four-dimensional Peccei-Quinn breaking scale f_{PQ}, compared with the solar QCD axion limit. Specifically, for the 57Fe experiment, f_{PQ}>1x10^6 GeV in theories with two extra dimensions and a higher-dimensional gravitational scale M_H of order 100 TeV, and f_{PQ}>1x10^6 GeV in theories with three extra dimensions and M_H of order 1 TeV (to be compared with the QCD axion limit, f_{PQ}>8x10^3 GeV). For the 7Li experiment, f_{PQ}>1.4x10^5 GeV and 3.4x10^5 GeV, respectively (to be compared with the QCD axion limit, f_{PQ}>1.9x10^2 GeV). It is an interesting feature of our results that, in most cases, the obtained limit on f_{PQ} cannot be coupled with the mass of the axion, which is essentially set by the (common) radius of the extra dimensions.
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Axions generated thermally in the solar core can convert nearly directly to X-rays as they pass through the solar atmosphere via interaction with the magnetic field. The result of this conversion process would be a diffuse centrally-concentrated source of few-keV X-rays at disk center; it would have a known dimension, of order 10% of the solar diameter, and a spectral distribution resembling the blackbody spectrum of the solar core. Its spatial structure in detail would depend on the distribution of mass and field in the solar atmosphere. The brightness of the source depends upon these factors as well as the unknown coupling constant and the unknown mass of the axion; this particle is hypothetical and no firm evidence for its existence has been found yet. We describe the solar magnetic environment as an axion/photon converter and discuss the upper limits obtained by existing and dedicated observations from three solar X-ray observatories: Yohkoh, RHESSI, and Hinode
A search for resonant absorption of the solar axion by $^{83}rm{Kr}$ nuclei was performed using the proportional counter installed inside the low-background setup at the Baksan Neutrino Observatory. The obtained model independent upper limit on the combination of isoscalar and isovector axion-nucleon couplings $|g_3-g_0|leq 8.4times 10^{-7}$ allowed us to set the new upper limit on the hadronic axion mass of $m_{A}leq 65$ eV (95% C.L.) with the generally accepted values $S$=0.5 and $z$=0.56.
Models in which gravity and/or Standard Model gauge bosons propagate in more than three spatial dimensions have implications that can be tested at current colliders. In this paper, we report on the results from searches for extra dimensions at the two Tevatron experiments, CDF and D0, which utilize up to 200 pb^-1 of proton-antiproton collision data from Run II taken at 1.96 TeV CoM energy, between spring 2002 and fall 2003.
We consider a model where right-handed neutrinos propagate in a large compactified extra dimension, engendering Kaluza-Klein (KK) modes, while the standard model particles are restricted to the usual 4-dimensional brane. A mass term mixes the KK modes with the standard left-handed neutrinos, opening the possibility of change the 3 generation mixing pattern. We derive bounds on the maximum size of the extra dimension from neutrino oscillation experiments. We show that this model provides a possible explanation for the deficit of nu_e in Ga solar neutrino calibration experiments and of the anti-nu_e in short baseline reactor experiments.
The holographic principle asserts that the entropy of a system cannot exceed its boundary area in Planck units. However, conventional quantum field theory fails to describe such systems. In this Letter, we assume the existence of large $n$ extra dimensions and propose a relationship between UV and IR cutoffs in this case. We find that if $n=2$, this effective field theory could be a good description of holographic systems. If these extra dimensions are detected in future experiments, it will help to prove the validity of the holographic principle. We also discuss implications for the cosmological constant problem.
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