Direct Detection Signals Research Articles

Asymmetric dark matter from hidden sector baryogenesis

We consider the production of asymmetric dark matter during hidden sector baryogenesis. We consider a particular supersymmetric model where the dark matter candidate has a number density approximately equal to the baryon number density, with a mass of the same scale as the b, c and τ. Both baryon asymmetry and dark matter are created at the same time in this model. We describe collider and direct detection signatures of this model.

Thermal leptogenesis and the gravitino problem in the Asaka-Yanagida axion/axino dark matter scenario

A successful implementation of thermal leptogenesis requires the re-heat temperature after inflation TR to exceed ∼ 2 × 109 GeV. Such a high TR value typically leads to an overproduction of gravitinos in the early universe, which will cause conflicts, mainly with BBN constraints. Asaka and Yanagida (AY) have proposed that these two issues can be reconciled in the context of the Peccei-Quinn augmented MSSM (PQMSSM) if one adopts a mass hierarchy m(sparticle) > m(gravitino)>m(axino), with m(axino) ∼ keV. In this case, sparticle decays bypass the gravitino, and decay more quickly to the axino LSP, thus avoiding the BBN constraints. In addition, thermally produced gravitinos decay inertly to axion+axino, also avoiding BBN constraints. We calculate the relic abundance of mixed axion/axino dark matter in the AY scenario, and investigate under what conditions a value of TR sufficient for thermal leptogenesis can be generated. A high value of PQ breaking scale fa is needed to suppress overproduction of axinos, while a small vacuum misalignment angle θi is needed to suppress overproduction of axions. The large value of fa results in late decaying neutralinos. We show that, to avoid BBN constraints, the AY scenario requires a rather low thermal abundance of neutralinos, while higher values of neutralino mass also help. We combine these constraint calculations along with entropy production from late decaying saxions, and find the saxion needs to be typically at least several times heavier than the gravitino. A successful implementation of the AY scenario suggests that LHC should discover a spectrum of SUSY particles consistent with weak scale supergravity; that the apparent neutralino abundance is low; that an axion direct detection signal (probably with ma in the sub-μeV range) may be possible, but no direct or indirect signals for WIMP dark matter should be observed.

Reconciling thermal leptogenesis with the gravitino problem in SUSY models with mixed axion/axino dark matter

Successful implementation of thermal leptogenesis requires re-heattemperatures TR≳2 × 109 GeV, in apparent conflict with SUSY models with TeV-scale gravitinos, which require much lower TR in order to avoid Big Bang Nucleosynthesis (BBN) constraints. We show that mixed axion/axino dark matter can reconcile thermal leptogenesis with the gravitino problem in models with mG̃≳30 TeV, a rather high Peccei-Quinn breaking scaleand an initial mis-alignment angle θi < 1.We calculate axion and axino dark matter production from four sources, and impose BBN constraints on long-lived gravitinos and neutralinos.Moreover, we discuss several SUSY models which naturally have gravitino masses of the order of tens of TeV.We find a reconciliation difficult in Yukawa-unified SUSY and in AMSB with a wino-like lightest neutralino. However, TR ∼ 1010−1012 GeV can easily be achieved in effective SUSY and in models based on mixed moduli-anomaly mediation. Consequences of this scenario include: 1. an LHC SUSY discovery should be consistentwith SUSY models with a large gravitino mass,2. an apparent neutralino relic abundance ΩZ̃1h2≲1,3. no WIMP direct or indirect detection signals should be found, and 4. the axion mass should be less than ∼ 10−6 eV, somewhat below the conventional range which is explored by microwave cavity axion detection experiments.

Dependence of direct detection signals on the WIMP velocity distribution

The signals expected in WIMP direct detection experiments depend on the ultra-local dark matter distribution. Observations probe the local density, circular speed and escape speed, while simulations find velocity distributions that deviate significantly from the standard Maxwellian distribution. We calculate the energy, time and direction dependence of the event rate for a range of velocity distributions motivated by recent observations and simulations, and also investigate the uncertainty in the determination of WIMP parameters. The dominant uncertainties are the systematic error in the local circular speed and whether or not the MW has a high density dark disc. In both cases there are substantial changes in the mean differential event rate and the annual modulation signal, and hence exclusion limits and determinations of the WIMP mass. The uncertainty in the shape of the halo velocity distribution is less important, however it leads to a ∼ 5% systematic error in the WIMP mass. The detailed direction dependence of the event rate is sensitive to the velocity distribution. However the numbers of events required to detect anisotropy and confirm the median recoil direction do not change substantially.

Impact of dark matter microhalos on signatures for direct and indirect detection

Detecting dark matter as it streams through detectors on Earth relies on knowledge of its phase space density on a scale comparable to the size of our solar system. Numerical simulations predict that our Galactic halo contains an enormous hierarchy of substructures, streams and caustics, the remnants of the merging hierarchy that began with tiny Earth mass microhalos. If these bound or coherent structures persist until the present time, they could dramatically alter signatures for the detection of weakly interacting elementary particle dark matter (WIMP). Using numerical simulations that follow the coarse grained tidal disruption within the Galactic potential and fine grained heating from stellar encounters, we find that microhalos, streams and caustics have a negligible likelihood of impacting direct detection signatures implying that dark matter constraints derived using simple smooth halo models are relatively robust. We also find that many dense central cusps survive, yielding a small enhancement in the signal for indirect detection experiments.

Astrophysical limitations to the identification of dark matter: Indirect neutrino signalsvis-à-visdirect detection recoil rates

A convincing identification of dark matter (DM) particles can probably be achieved only through a combined analysis of different detections strategies, which provides an effective way of removing degeneracies in the parameter space of DM models. In practice, however, this program is made complicated by the fact that different strategies depend on different physical quantities, or on the same quantities but in a different way, making the treatment of systematic errors rather tricky. We discuss here the uncertainties on the recoil rate in direct-detection experiments and on the muon rate induced by neutrinos from dark matter annihilations in the Sun, and we show that, contrarily to the local DM density or overall cross section scale, irreducible astrophysical uncertainties affect the two rates in a different fashion, therefore limiting our ability to reconstruct the parameters of the dark matter particles. By varying within their respective errors astrophysical parameters such as the escape velocity and the velocity dispersion of dark matter particles, we show that the uncertainty on the relative strength of the neutrino and direct-detection signal is as large as a factor of 2 for typical values of the parameters, but can be even larger in some circumstances.

Erratum: scalar multiplet dark matter

We perform a systematic study of the phenomenology associated to models where the dark matter consists in the neutral component of a scalar SU(2)_L n-uplet, up to n=7. If one includes only the pure gauge induced annihilation cross-sections it is known that such particles provide good dark matter candidates, leading to the observed dark matter relic abundance for a particular value of their mass around the TeV scale. We show that these values actually become ranges of values -which we determine- if one takes into account the annihilations induced by the various scalar couplings appearing in these models. This leads to predictions for both direct and indirect detection signatures as a function of the dark matter mass within these ranges. Both can be largely enhanced by the quartic coupling contributions. We also explain how, if one adds right-handed neutrinos to the scalar doublet case, the results of this analysis allow to have altogether a viable dark matter candidate, successful generation of neutrino masses, and leptogenesis in a particularly minimal way with all new physics at the TeV scale.

Chaos-on-a-chip secures data transmission in optical fiber links

Security in information exchange plays a central role in the deployment of modern communication systems. Besides algorithms, chaos is exploited as a real-time high-speed data encryption technique which enhances the security at the hardware level of optical networks. In this work, compact, fully controllable and stably operating monolithic photonic integrated circuits (PICs) that generate broadband chaotic optical signals are incorporated in chaos-encoded optical transmission systems. Data sequences with rates up to 2.5 Gb/s with small amplitudes are completely encrypted within these chaotic carriers. Only authorized counterparts, supplied with identical chaos generating PICs that are able to synchronize and reproduce the same carriers, can benefit from data exchange with bit-rates up to 2.5Gb/s with error rates below 10(-12). Eavesdroppers with access to the communication link experience a 0.5 probability to detect correctly each bit by direct signal detection, while eavesdroppers supplied with even slightly unmatched hardware receivers are restricted to data extraction error rates well above 10(-3).

Dark matter direct detection signals inferred from a cosmological N-body simulation with baryons

We extract at redshift z = 0 a Milky Way sized object including gas, stars and dark matter (DM) from a recent, high-resolution cosmological N-body simulation with baryons. Its resolution is sufficient to witness the formation of a rotating disk and bulge at the center of the halo potential,therefore providing a realistic description of the birth and the evolution of galactic structures in the ΛCDM cosmology paradigm.The phase-space structure of the central galaxy reveals that, throughout a thick region, the dark halo is co-rotating on average with the stellar disk.At the Earth's location, the rotating component, sometimes called dark disk in the literature,is characterized by a minimum lag velocity vlag ≃ 75 km/s,in which case it contributes to around 25% of the total DM local density, whose value is ρDM ≃ 0.37GeV/cm3.The velocity distributions also show strong deviations from pure Gaussian and Maxwellian distributions, with a sharper drop of the high velocity tail.We give a detailed study of the impact of these features on the predictions for DM signals in direct detection experiments.In particular, the question of whether the modulation signal observed by DAMA is or is not excluded by limits set by otherexperiments (CDMS, XENON and CRESST…) is re-analyzed and compared to the case of a standard Maxwellian halo.We consider spin-independent interactions for both the elastic and the inelastic scattering scenarios.For the first time, we calculate the allowed regions for DAMA and the exclusion limits of other null experimentsdirectly from the velocity distributions found in the simulation. We then compare these results with the predictions of various analytical distributions.We find that the compatibility between DAMA and the other experiments is improved.In the elastic scenario, the DAMA modulation signal is slightly enhanced in the so-called channeling region,as a result of several effects that include a departure from a Maxwellian distribution and anisotropiesin the velocity dispersions due to the dark disk.For the inelastic scenario, the improvement of the fit is mainly attributable to the departure from a Maxwellian distribution at high velocity.It is correctly modeled by a generalized Maxwellian distribution with a parameter α ≃ 1.95, or by a Tsallis distributionwith q ≃ 0.75.

SEARCHING FOR AXIONS AND OTHER EXOTICS WITH DARK MATTER DETECTORS

I consider models of light super-weakly interacting cold dark matter, with [Formula: see text] mass, focusing on bosonic candidates such as pseudoscalars and vectors. I analyze the cosmological abundance, the γ-background created by particle decays, the impact on stellar processes due to cooling, and the direct detection capabilities in order to identify classes of models that pass all the constraints. In certain models, variants of photoelectric (or axioelectric) absorption of dark matter in direct-detection experiments can provide a sensitivity to the superweak couplings to the Standard Model which is superior to all existing indirect constraints. In all models studied, the annual modulation of the direct-detection signal is at the currently unobservable level of O(10-5).

Direct search for dark matter—striking the balance—and the future

Weakly Interacting Massive Particles (WIMPs) are among the main candidates for the relic dark matter (DM). The idea of the direct DM detection relies on elastic spin-dependent (SD) and spin-independent (SI) interaction of WIMPs with target nuclei. In this review paper the relevant formulae for WIMP event rate calculations are collected. For estimations of the WIMP-proton and WIMP-neutron SD and SI cross sections the effective low-energy minimal supersymmetric standard model is used. The traditional one-coupling-dominance approach for evaluation of the exclusion curves is described. Further, the mixed spin-scalar coupling approach is discussed. It is demonstrated, taking the high-spin 73Ge dark matter experiment HDMS as an example, how one can drastically improve the sensitivity of the exclusion curves within the mixed spin-scalar coupling approach, as well as due to a new procedure of background subtraction from the measured spectrum. A general discussion on the information obtained from exclusion curves is given. The necessity of clear WIMP direct detection signatures for a solution of the dark matter problem, is pointed out.

Scalar multiplet dark matter

We perform a systematic study of the phenomenology associated to models where the dark matter consists in the neutral component of a scalar SU(2)L n-uplet, up to n = 7. If one includes only the pure gauge induced annihilation cross-sections it is known that such particles provide good dark matter candidates, leading to the observed dark matter relic abundance for a particular value of their mass around the TeV scale. We show that these values actually become ranges of values - which we determine - if one takes into account the annihilations induced by the various scalar couplings appearing in these models. This leads to predictions for both direct and indirect detection signatures as a function of the dark matter mass within these ranges. Both can be largely enhanced by the quartic coupling contributions. We also explain how, if one adds right-handed neutrinos to the scalar doublet case, the results of this analysis allow to have altogether a viable dark matter candidate, successful generation of neutrino masses, and leptogenesis in a particularly minimal way with all new physics at the TeV scale.

Auxin and Ethylene Regulate Elongation Responses to Neighbor Proximity Signals Independent of Gibberellin and DELLA Proteins in Arabidopsis

Plants modify growth in response to the proximity of neighbors. Among these growth adjustments are shade avoidance responses, such as enhanced elongation of stems and petioles, that help plants to reach the light and outgrow their competitors. Neighbor detection occurs through photoreceptor-mediated detection of light spectral changes (i.e. reduced red:far-red ratio [R:FR] and reduced blue light intensity). We recently showed that physiological regulation of these responses occurs through light-mediated degradation of nuclear, growth-inhibiting DELLA proteins, but this appeared to be only part of the full mechanism. Here, we present how two hormones, auxin and ethylene, coregulate DELLAs but regulate shade avoidance responses through DELLA-independent mechanisms in Arabidopsis (Arabidopsis thaliana). Auxin appears to be required for both seedling and mature plant shoot elongation responses to low blue light and low R:FR, respectively. Auxin action is increased upon exposure to low R:FR and low blue light, and auxin inhibition abolishes the elongation responses to these light cues. Ethylene action is increased during the mature plant response to low R:FR, and this growth response is abolished by ethylene insensitivity. However, ethylene is also a direct volatile neighbor detection signal that induces strong elongation in seedlings, possibly in an auxin-dependent manner. We propose that this novel ethylene and auxin control of shade avoidance interacts with DELLA abundance but also controls independent targets to regulate adaptive growth responses to surrounding vegetation.

Bosonic super-WIMPs as keV-scale dark matter

We consider models of light superweakly interacting cold dark matter, with $\mathcal{O}(10--100)\text{ }\text{ }\mathrm{keV}$ mass, focusing on bosonic candidates such as pseudoscalars and vectors. We analyze the cosmological abundance, the $\ensuremath{\gamma}$ background created by particle decays, the impact on stellar processes due to cooling, and the direct-detection capabilities in order to identify classes of models that pass all the constraints. In certain models, variants of photoelectric (or axioelectric) absorption of dark matter in direct-detection experiments can provide a sensitivity to the superweak couplings to the standard model which is superior to all existing indirect constraints. In all models studied, the annual modulation of the direct-detection signal is at the currently unobservable level of $O({10}^{\ensuremath{-}5})$.

Resonant scattering and recombination of pseudodegenerate WIMPs

We consider the direct and indirect detection signatures of weakly interacting massive particles (WIMPs) {chi}{sup 0} in kinematic regimes with a heavier, but nearly degenerate, charged state {chi}{sup {+-}}. For small splittings of O(10) MeV, the scattering of WIMPs off nuclei may be dominated by inelastic recombination processes mediated by the formation of ({chi}{sup -}N) bound states, leading to a distinct signature for direct detection. These cross sections are bound primarily by limits on the abundance of heavy isotopes, and may be considerably larger than the elastic scattering cross section in more conventional models. If the mass splitting is too large for recombination to occur, there may still be a significant resonant enhancement of loop-induced electromagnetic form factors of the WIMP, which can enhance the elastic scattering cross section. We also discuss how this regime affects the annihilation cross section and indirect detection signatures, and note the possibility of a significant mono-energetic {gamma} signal, mediated by resonant processes near the ({chi}{sup +}{chi}{sup -}) bound-state threshold.

Microwave reflection amplifier for detection and tagging applications

A reflection amplifier module with up to 14 dB gain at 21 GHz is described, which is capable of direct detection of amplitude modulated incident signals at K band. The module consists of a single pseudomorphic high electron mobility transistor (pHEMT) transistor gallium arsenide integrated circuit attached to a microstrip patch antenna. Experimental sensitivity characteristics for the module are given for several bias conditions. These results show that the module is capable of direct detection of signals as low as −75 dBm. In addition, reflection gain control through d.c. bias modification is used to directly encode amplitude modulated backscattered information onto the amplified signal returned by the reflection amplifier tag. The authors also show how the incorporation of an ultra-thin absorber with the tag can be used to increase its re-transmitted signal performance characteristics.

A new strategy for fast radiofrequency CW EPR imaging: Direct detection with rapid scan and rotating gradients

Rapid field scan on the order of T/s using high frequency sinusoidal or triangular sweep fields superimposed on the main Zeeman field, was used for direct detection of signals without low-frequency field modulation. Simultaneous application of space-encoding rotating field gradients have been employed to perform fast CW EPR imaging using direct detection that could, in principle, approach the speed of pulsed FT EPR imaging. The method takes advantage of the well-known rapid-scan strategy in CW NMR and EPR that allows arbitrarily fast field sweep and the simultaneous application of spinning gradients that allows fast spatial encoding. This leads to fast functional EPR imaging and, depending on the spin concentration, spectrometer sensitivity and detection band width, can provide improved temporal resolution that is important to interrogate dynamics of spin perfusion, pharmacokinetics, spectral spatial imaging, dynamic oxymetry, etc.

Analysis of direct-detection DPSK signal with homodyne crosstalk

When a differential-phase-shift-keying (DPSK) signal is directly detected using an asymmetric interferometer and balanced receiver, the exact error probability of the signal with homodyne crosstalk is derived analytically. Homodyne crosstalk from many interferers is Gaussian distributed, but the Gaussian model overestimates the signal-to-noise ratio (SNR) penalty for homodyne crosstalk from a single interferer. For the DPSK signal, the crosstalk ratio for a 1-dB SNR penalty must be less than -16.5 dB. For the same crosstalk ratio, the SNR penalty for a DPSK signal is far smaller than that for an ON-OFF keying (OOK) signal.

The first WIMPy halos

Dark matter direct and indirect detection signals depend crucially on the dark matterdistribution. While the formation of large scale structure is independent of the nature ofthe cold dark matter (CDM), the fate of inhomogeneities on subgalactic scales, and hencethe present day CDM distribution on these scales, depends on the microphysics of theCDM particles. We study the density contrast of weakly interacting massive particles(WIMPs) on subgalactic scales. We calculate the damping of the primordial powerspectrum due to collisional damping and free streaming of WIMPy CDM and show thatfree streaming leads to a CDM power spectrum with a sharp cut-off at about. We also calculate the transfer function for the growth of the inhomogeneities in the linearregime, taking into account the suppression in the growth of the CDM densitycontrast after matter–radiation equality due to baryons and show that our analyticresults are in good agreement with numerical calculations. Combining the transferfunction with the damping of the primordial fluctuations we produce a WMAPnormalized primordial CDM power spectrum, which can serve as an input for highresolution CDM simulations. We find that the smallest inhomogeneities typically havecomoving radius of about 1 pc and enter the non-linear regime at a red-shift of60 ± 20. We study the effect of scale dependence of the primordial power spectrum on thesenumbers and also use the spherical collapse model to make simple estimates of theproperties of the first generation of WIMP halos to form. We find that the very firstWIMPy halos may have a significant impact on indirect dark matter searches.

Different halo models and DAMA/CDMS/EDELWEISS and future detectors

We compare the sensitivity of WIMP detection via direct separation of possible signal vs. background to WIMP detection via detection of an annual modulation, in which signal and background cannot be separated on an event-by-event basis. In order to determine how the constraints from the two different types of experiments might be combined an adequate incorporation of uncertainties due to galactic halo models must be made. This issue is particularly timely in light of recent direct detection limits from Edelweiss and CDMS, which we now demonstrate cannot be made consistent with the most recent claimed DAMA annual modulation observation, even by including halo uncertainties for spin-independent interactions. On the other hand, we demonstrate that a combination of these two techniques, in the event of any positive direct detection signal, could ultimately allow significant constraints on anisotropic halo models even without directional sensitivity in these detectors. For direction-sensitive detectors we derive a new formalism to calculate angular event rates, and present the predicted angular signal for a variety of halo models and calculate the number of events needed to distinguish a dark matter signal from an isotropic background.