arXiv subjects

K. Zioutas

Publications and source records attributed to K. Zioutas.

69 records · Page 4Linked to original sources

arXiv2007

The CAST Time Projection Chamber

One of the three X-ray detectors of the CAST experiment searching for solar axions is a Time Projection Chamber (TPC) with a multi-wire proportional counter (MWPC) as a readout structure. Its design has been optimized to provide high sensitivity to the detection of the low intensity X-ray signal expected in the CAST experiment. A low hardware threshold of 0.8 keV is safely set during normal data taking periods, and the overall efficiency for the detection of photons coming from conversion of solar axions is 62 %. Shielding has been installed around the detector, lowering the background level to 4.10 x 10^-5 counts/cm^2/s/keV between 1 and 10 keV. During phase I of the CAST experiment the TPC has provided robust and stable operation, thus contributing with a competitive result to the overall CAST limit on axion-photon coupling and mass.

physics.ins-det↗

arXiv2006

Indirect signatures for axion(-like) particles

Magnetic field dependent transient solar observations are suggestive for axion-photon oscillations with light axion(-like) particle involvement. Novel dark-moon measurements with the SMART X-ray detectors can be conclusive for radiatively decaying massive exotica like the generic solar Kaluza-Klein axions. Furthermore, the predicted intrinsic strong solar magnetic fields could be the reason of enhanced low energy axion production. Such an axion component could be the as yet unknown origin of the strong quiet Sun X-ray luminosity at energies below 1 keV. Solar axion telescopes should lower their threshold, aiming to copy processes that might occur near the solar surface, be it due to spontaneous or magnetically induced radiative decay of axion(-like) particles. This is motivated also by the recent claim of an axion-like particle detection by the laser experiment PVLAS.

astro-ph↗

arXiv2005

Guidelines for axion identification in astrophysical observations

The origin of various celestial phenomena have remained mysterious for conventional astrophysics. Therefore, alternative solutions should be considered, taking into account the involvement of unstable dark-matter particle candidates, such as the celebrated axions or other as yet unforeseen axion-like particles. Their spontaneous and induced decay by the ubiquitous solar magnetic fields can be at the origin of persisting enigmatic X-ray emission, giving rise to a steady and a transient/local solar activity, respectively. The (coherent) conversion of photons into axion(-like) particles in intrinsic magnetic fields may modify the solar axion spectrum. The reversed process can be behind transient (solar) luminosity deficits in the visible. Then, the Sun might be also a strong source of ~eV-axions. Thus, enigmatic observations might be the as yet missing direct signature for axion(-like) particles in earth-bound detectors.

astro-ph↗

arXiv2004

Solar X-rays as Signature for New Particles

Massive axions of the Kaluza-Klein type, created inside the solar core, can be gravitationally trapped by the Sun itself in orbits inside/outside the Sun, where they accumulate over cosmic times. Their radiative decay can give rise to various solar phenomena, like the celebrated solar coronal heating, which lacks a conventional explanation since its first observation in 1939. Such and other recent observations favour the existence of a halo of exotic particles near the Sun. X-ray telescopes can provide novel and important information. The underlying solar axion scenario is presented in details in ref.'s [4,15]

astro-ph↗

arXiv2004

Quiet Sun X-rays as Signature for New Particles

We have studied published data from the Yohkoh solar X-ray mission, with the purpose of searching for signals from radiative decays of new, as yet undiscovered massive neutral particles. This search is based on the prediction that solar axions of the Kaluza-Klein type should result in the emission of X-rays from the Sun direction beyond the limb with a characteristic radial distribution. These X-rays should be observed more easily during periods of quiet Sun. An additional signature is the observed emission of hard X-rays by SMM, NEAR and RHESSI. The recent observation made by RHESSI of a continuous emission from the non-flaring Sun of X-rays in the 3 to ~15 keV range fits the generic axion scenario. This work also suggests new analyses of existing data, in order to exclude instrumental effects; it provides the rationale for targeted observations with present and upcoming (solar) X-ray telescopes, which can provide the final answer on the nature of the signals considered here. Such measurements become more promising during the forthcoming solar cycle minimum with an increased number of quiet Sun periods.

astro-ph↗

arXiv2002

Observational evidence for gravitationally trapped massive axion(-like) particles

Unexpected astrophysical observations can be explained by gravitationally captured massive particles, which are produced inside the Sun or other Stars and are accumulated over cosmic times. Their radiative decay in solar outer space would give rise to a `self-irradiation' of the whole star, providing the time-independent component of the corona heating source. In analogy with the Sun-irradiated Earth atmosphere, the temperature and density gradient in the corona - chromosphere transition region is suggestive for an omnipresent irradiation of the Sun. The same scenario fits other astrophysical X-ray observations. The radiative decay of a population of such elusive particles mimics a hot gas. X-ray observatories, with an unrivalled sensitivity below ~10 keV, can search for such particles. The elongation angle relative to the Sun is the relevant new parameter.

astro-ph↗

arXiv2000

Search for solar Kaluza-Klein axions in theories of low-scale quantum gravity

We explore the physics potential of a terrestrial detector for observing axionic Kaluza-Klein excitations coming from the Sun within the context of higher-dimensional theories of low-scale quantum gravity. In these theories, the heavier Kaluza-Klein axions are relatively short-lived and may be detected by a coincidental triggering of their two-photon decay mode. Because of the expected high multiplicity of the solar axionic excitations, we find experimental sensitivity to a fundamental Peccei-Quinn axion mass up to $10^{-2}$ eV (corresponding to an effective axion-photon coupling $g_{aγγ} \approx 2.\times 10^{-12}$ GeV$^{-1}$) in theories with 2 extra dimensions and a fundamental quantum-gravity scale $M_{\rm F}$ of order 100 TeV, and up to $3.\times 10^{-3}$ eV (corresponding to $g_{aγγ} \approx 6.\times 10^{-13}$ GeV$^{-1}$) in theories with 3 extra dimensions and $M_{\rm F}=1$ TeV. For comparison, based on recent data obtained from lowest level underground experiments, we derive the experimental limits: $g_{a γγ} \stackrel{<}{{}_\sim} 2.5\times 10^{-11}$ GeV$^{-1}$ and $g_{a γγ} \stackrel{<}{{}_\sim} 1.2\times 10^{-11}$ GeV$^{-1}$ in the aforementioned theories with 2 and 3 large compact dimensions, respectively.

hep-ph↗

arXiv1999

Constraints on Exotic Heavily Ionizing Particles from the Geological Abundance of Fullerenes

The C_{60} molecule exhibits a remarkable stability and inertness that leads to its survival in ancient carbonaceous rocks initially subject to the high temperatures requisite for its formation. Elementary particles having very high electronic stopping powers can similarly form C_{60} and higher fullerenes in their wake. Combined, these two features point at the possibility of using the C_{60} presence (or absence) in selected bulk geological samples as a new type of solid-state nuclear track detector, with applications in astro-particle physics.

astro-ph↗

arXiv1999

A Decommissioned LHC Model Magnet as an Axion Telescope

The 8.4 Tesla, 10 m long transverse magnetic field of a twin aperture LHC bending magnet can be utilized as a macroscopic coherent solar axion-to-photon converter. Numerical calculations show that the integrated time of alignment with the Sun would be 33 days per year with the magnet on a tracking table capable of $\pm 5^o$ in the vertical direction and $\pm 40^o$ in the horizontal direction. The existing lower bound on the axion-to-photon coupling constant can be improved by a factor between 50 and 100 in 3 years, i.e., $g_{aγγ} \lesssim 9\cdot 10^{-11} GeV^{-1}$ for axion masses $\lesssim$ 1 eV. This value falls within the existing open axion mass window. The same set-up can simultaneously search for low- and high-energy celestial axions, or axion-like particles, scanning the sky as the Earth rotates and orbits the Sun.

astro-ph↗

arXiv1998

Search for energetic cosmic axions utilizing terrestrial/celestial magnetic fields

Orbiting $γ$-detectors combined with the magnetic field of the Earth or the Sun can work parasitically as cosmic axion telescopes. The relatively short field lengths allow the axion-to-photon conversion to be coherent for $m_{axion} \sim 10^{-4}$ eV, if the axion kinetic energy is above $\sim 500$ keV (Earth's field), or, $\sim 50$ MeV (Sun's field), allowing thus to search for axions from $e^+e^-$ annihilations, from supernova explosions, etc. With a detector angular resolution of $\sim 1^o$, a more efficient sky survey for energetic cosmic axions passing {\it through the Sun} can be performed. Axions or other axion-like particles might be created by the interaction of the cosmic radiation with the Sun, similarly to the axion searches in accelerator beam dump experiments; the enormous cosmic energy combined with the built-in coherent Primakoff effect might provide a sensitive detection scheme, being out of reach with accelerators. The axion signal will be an excess in $γ$-rays coming either from a specific celestial place behind the Sun, e.g. the Galactic Center, or, from any other direction in the sky being associated with a violent astrophysical event, e.g. a supernova. Earth bound detectors are also of potential interest. The axion scenario also applies to other stars or binary systems in the Universe, in particular to those with superstrong magnetic fields.

astro-ph↗

arXiv1998

Ferroelectrics and their possible involvement in Biology

We present the main properties of ferroelectricity, with emphasis given to a specific family of hydrated ferroelectric crystals, which can serve as model systems for corresponding configurations in biology like the microtubules. An experimental method is described, which allows to establish the ferroelectric property of microtubules in suspension.

quant-ph↗

arXiv1997

Experimental Search for Solar Axions

A new technique has been used to search for solar axions using a single crystal germanium detector. It exploits the coherent conversion of axions into photons when their angle of incidence satisfies a Bragg condition with a crystalline plane. The analysis of approximately 1.94 kg.yr of data from the 1-kg DEMOS detector in Sierra Grande, Argentina, yields a new laboratory bound on axion-photon coupling of g_{a,γγ}<2.7\times 10^{-9} GeV^{-1} independent of axion mass up to \sim 1 keV.

astro-ph↗

arXiv1997

Theory for the Direct Detection of Solar Axions by Coherent Primakoff Conversion in Germanium Detectors

It is assumed that axions exist and are created in the Sun by Primakoff conversion of photons in the Coulomb fields of nuclei. Detection rates are calculated in germanium detectors due to the coherent conversion of axions to photons in the lattice when the incident angle fulfills the Bragg condition for a given crystalline plane. The rates are correlated with the relative positions of the Sun and detector, yielding a characteristic recognizable sub-diurnal temporal pattern. A major experiment is proposed based on a large detector array.

hep-ph↗

arXiv1997

Experimental Search for Solar Axions via Coherent Primakoff Conversion in a Germanium Spectrometer

Results are reported of an experimental search for the unique, rapidly varying temporal pattern of solar axions coherently converting into photons via the Primakoff effect in a single crystal germanium detector. This conversion is predicted when axions are incident at a Bragg angle with a crystalline plane. The analysis of approximately 1.94 kg.yr of data from the 1 kg DEMOS detector in Sierra Grande, Argentina, yields a new laboratory bound on axion-photon coupling of $g_{aγγ} < 2.7\cdot 10^{-9}$ GeV$^{-1}$, independent of axion mass up to ~ 1 keV.

astro-ph↗

arXiv1996

On the Interaction of Extreme-Low-Frequency Radiation with Living Matter's Coherent Spiral States

Conventional physics cannot explain bioeffects caused by ELF fields [1]. A (double) resonance interaction of ELF radiation with the highly sub-thermal coherent motion of spiral waves in living matter (LM) is suggested. The (geo)magnetic cyclotron resonance (CR) absorption by the constituent ions can drastically change their non-thermal degrees of freedom in the spiral state, destroying their pattern, which is heuristically assumed to be part of the cell signaling. Combining ELF irradiation with calcium imaging to unravel the suggested mechanism, a new instrument in biomedicine might emerge. These fascinating waves, being part of the bio-machinery, might provide insight in cancer, embryogenesis, etc., as they are affected by ELF radiation in an as yet unknown manner [2-6].

patt-sol↗