Abstract We discuss the problem of constructing a model in which supersymmetry is unbroken down to low energies. It is suggested that the scalar partners of quarks and leptons may get their masses through radiative corrections and that the breaking of the weak interactions also occurs through radiative corrections. A toy model is constructed which illustrates these ideas.

Low-energy supersymmetry

We report results of a search for Weakly Interacting Massive Particles (WIMPS) with the silicon detectors of the CDMS II experiment. This blind analysis of 140.2 kg-days of data taken between July 2007 and September 2008 revealed three WIMP-candidate events with a surface-event background estimate of 0.41^{+0.20}_{-0.08}(stat.)^{+0.28}_{-0.24}(syst.). Other known backgrounds from neutrons and 206Pb are limited to < 0.13 and <0.08 events at the 90% confidence level, respectively. The exposure of this analysis is equivalent to 23.4 kg-days for a recoil energy range of 7-100 keV for a WIMP of mass 10 GeV/c2. The probability that the known backgrounds would produce three or more events in the signal region is 5.4%. A profile likelihood ratio test of the three events that includes the measured recoil energies gives a 0.19% probability for the known-background-only hypothesis when tested against the alternative WIMP+background hypothesis. The highest likelihood occurs for a WIMP mass of 8.6 GeV/c2 and WIMP-nucleon cross section of 1.9e-41 cm2.

Silicon Detector Dark Matter Results from the Final Exposure of CDMS II

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Observation of a New Boson at a Mass of 125 GEV with the Cms Experiment at the Lhc

The relic abundance and the scalar cross section off the nucleon for light neutralinos (of mass below about 45 GeV) are evaluated in an effective MSSM model without GUT-inspired relations among the gaugino masses. It is shown that these neutralinos may provide a sizable contribution to the matter density in the Universe and produce measurable effects in WIMP direct detection experiments. These properties are elucidated in terms of simple analytical arguments.

Light Relic Neutralinos

The XENON1T experiment at the Laboratori Nazionali del Gran Sasso (LNGS) is the first WIMP dark matter detector operating with a liquid xenon target mass above the ton-scale. Out of its 3.2 t liquid xenon inventory, 2.0 t constitute the active target of the dual-phase time projection chamber. The scintillation and ionization signals from particle interactions are detected with low-background photomultipliers. This article describes the XENON1T instrument and its subsystems as well as strategies to achieve an unprecedented low background level. First results on the detector response and the performance of the subsystems are also presented.

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The XENON1T Dark Matter Experiment

Supersymmetry (SUSY) has been considered since long ago the leading paradigm of beyond the Standard Model (SM) physics as a framework that tackles the SM hierarchy problem, provides gauge coupling unification and a well-behaved cold dark matter (DM) candidate. Nevertheless, current experimental searches for new physics seem to have cornered the minimal versions of these models in unnatural regions of their parameter space, according to the standard Natural SUSY scenario. With the aim of formulating a general naturalness criterion for minimal supersymmetric scenarios, we have carefully re-examined the standard fine-tuning measure, which only deals with the cancellations needed to obtain the electroweak symmetry breaking (EWSB) scale, introducing several improvements such as the mixing of the fine-tuning conditions and the dependence on the low and high-energy (HE) scales. Furthermore, we have outlined a method that allow to straightforwardly derive naturalness bounds on the initial parameters and mass spectrum of any minimal supersymmetric standard model (MSSM) defined at any HE scale. We have applied this method to specific scenarios to compute a complete set of naturalness bounds. and also employed it to find the most natural gauge-mediated SUSY breaking model. Contrary to what was expected, we show that Natural SUSY, in general, does not demand light stops. The most stringent upper bound from naturalness is that of the gluino mass, which typically sets the level of fine-tuning, but strongly depends on the HE scale. The most robust result of Natural SUSY is by far that Higgsinos should be rather light. Besides, we have investigated other potential sources of fine cancellations in the MSSM, that if present, must be combined with that of the EWSB scale. The most important being the tuning to obtain the experimental Higgs mass and that required to reproduce the correct DM relic abundance. We have quantified them with p-value like measures that allow us to multiplicatively combine them with the electroweak (EW) fine-tuning. Regarding DM, we have considered the lightest neutralino as the DM particle and explored the various possibilities for its mass, composition and interactions that could give rise to accurate arrangements of the initial parameters to achieve the observed DM relic density. Finally, to illustrate the utility of the above stated criteria to estimate the global degree of naturalness, we have applied all of them to a specific model that features low-mass neutralinos and sleptons at low-energy. We find that these scenarios are rather unnatural when taking into account the aforementioned sources of tuning, which would have gone unnoticed, if we have only considered the EW fine-tuning.

The naturalness criterion for supersymmetric scenarios

We propose an operational definition for the local temperature of a quantum field employing Unruh-DeWitt detectors, as used in the study of the Unruh and Hawking effects. With this definition, an inhomogeneous quantum system in equilibrium can have different local temperatures, in analogy with the Tolman-Ehrenfest theorem from general relativity. We study the local temperature distribution on the ground state of hopping fermionic systems on a curved background. The observed temperature tends to zero as the thermometer-system coupling g vanishes. Yet, for small but finite values of g, we show that the product of the observed local temperature and the logarithm of the local speed of light is approximately constant. Our predictions should be testable on ultracold atomic systems.

Robles Portilla

Papers

The naturalness criterion for supersymmetric scenarios

Local quantum thermometry using Unruh-DeWitt detectors