Cent. Eur. J. Phys. • 9(3) • 2011 • 628-643 DOI: 10.2478/s11534-010-0075-z Central European Journal of Physics WIMP event rates in directional experiments: The diurnal variation signature Research Article John D. Vergados 1∗ , Charalampos C. Moustakidis 2† 1 Theoretical Physics Division, University of Ioannina, Ioannina, Gr 451 10, Greece 2 Department of Theoretical Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece Received 19 April 2010; accepted 11 August 2010 Abstract: The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmo- logical constant) dominate in the flat Universe. Modern particle theories provide viable cold dark matter candidates with masses in the GeV-TeV region. All such candidates will be called WIMPs (Weakly Inter- acting Massive Particles). The nature of dark matter can only be unraveled by its direct detection in the laboratory. In this work we present some theoretical elements relevant to the direct dark matter detection experiments, paying particular attention to directional experiments, i.e. experiments in which not only the energy but the direction of the recoiling nucleus is observed. Since the direction of observation is fixed with respect to the Earth, while the Earth is rotating around its axis, in a directional experiment the angle between the direction of observation and the Sun’s direction of motion will change during the day. So, since the event rates sensitively depend on this angle, the observed signal in such experiments will exhibit very interesting and characteristic periodic diurnal variation. PACS (2008): 95.35.+d, 12.60.Jv Keywords: dark matter • supersymmetric models © Versita Sp. z o.o. 1. Introduction The combined MAXIMA-1 [1–3], BOOMERANG [4–6], DASI [7, 8] and COBE/DMR Cosmic Microwave Back- ground (CMB) observations [9] imply that the Universe is flat [10] and that most of the matter in the Universe is Dark [11], i.e. exotic. These results have been confirmed ∗ E-mail: vergados@uoi.gr † E-mail: moustaki@auth.gr (Corresponding author) and improved by the recent WMAP data [12]. Combining the the data of these quite precise experiments one finds: Ω b =0.0456 ± 0.0015, Ω CDM =0.228 ± 0.013, Ω Λ =0.726 ± 0.015. Since any ”invisible” non exotic component cannot possi- bly exceed 40% of the above Ω CDM [13], exotic (non bary- onic) matter is required and there is room for cold dark matter candidates or WIMPs (Weakly Interacting Massive Particles). 628