Scattering rates for leptogenesis: Damping of lepton flavour coherence and production of singlet neutrinos

Using the Closed Time Path (CTP) approach, we perform a systematic leading order calculation of the relaxation rate of flavour correlations of left-handed Standard Model leptons. This quantity is of pivotal relevance for flavoured leptogenesis in the Early Universe, and we find it to be 5.19×10⁻³T$5.19\times {10}^{-3}T$ at T=10⁷ GeV$T={10}^7\text{GeV}$ and 4.83×10⁻³T$4.83\times {10}^{-3}T$ at T=10¹³ GeV$T={10}^{13}\text{GeV}$, in substantial agreement with estimates used in previous phenomenological analyses. These values apply to the Standard Model with a Higgs-boson mass of 125 GeV$125\text{GeV}$. The dependence of the numerical coefficient on the temperature T is due to the renormalisation group running. The leading linear and logarithmic dependencies of the flavour relaxation rate on the gauge and top-quark couplings are extracted, such that the results presented in this work can readily be applied to extensions of the Standard Model. We also derive the production rate of light (compared to the temperature) sterile right-handed neutrinos, a calculation that relies on the same methods. We confirm most details of earlier results, but find a substantially larger contribution from the t-channel exchange of fermions.     

Minimal Dirac fermionic dark matter with nonzero magnetic dipole moment

A neutral Dirac fermion ψ   with a nonzero magnetic dipole moment is supplied as a singlet within the context of the standard model and is considered as a dark matter candidate near the electroweak scale (10–1000 GeV$10\text{–}1000\text{GeV}$). We discuss its dynamics with the ordinary matters through the magnetic dipole moment. The magnetic dipole moment constrained by the relic abundance may be as large as ¹⁰⁻¹⁸–¹⁰⁻¹⁷e⋅cm${10}^{-18}\text{–}{10}^{-17}e\cdot \text{cm}$. We show that the elastic scattering is due to a spin–spin interaction for the direct detections and the predictions are under experimental exclusion limits of the current direct detectors, XENON10 and CDMS II, and consider the possibility of dark matter detection in the future.     

Critical revision of the ZEPLIN-I sensitivity to WIMP interactions

The ZEPLIN Collaboration has recently published its first result presenting a maximum sensitivity of 1.1×¹⁰⁻⁶$1.1\times {10}^{\mathrm{-6}}$ picobarn for a WIMP mass of ≈60 GeV$\approx 60\text{ GeV}$. The analysis is based on a discrimination method using the different time distribution of scintillation light generated in electron recoil and nuclear recoil interactions. We show that the methodology followed both for the calibration of the ZEPLIN-I detector response and for the estimation of the discrimination power is not reliable enough to claim any background discrimination at the present stage. The ZEPLIN-I sensitivity appears then to be in the order of 10⁻³ picobarn, three orders of magnitude above the claimed 1.1×¹⁰⁻⁶$1.1\times {10}^{\mathrm{-6}}$ picobarn.     

125 GeV Higgs,type III seesaw and gauge–Higgs unification

Recently, both the ATLAS and CMS experiments have observed an excess of events that could be the first evidence for a 125 GeV Higgs boson. This is a few GeV below the (absolute) vacuum stability bound on the Higgs mass in the Standard Model (SM), assuming a Planck mass ultraviolet (UV) cutoff. In this Letter, we study some implications of a 125 GeV Higgs boson for new physics in terms of the vacuum stability bound. We first consider the seesaw extension of the SM and find that in type III seesaw, the vacuum stability bound on the Higgs mass can be as low as 125 GeV for the seesaw scale around a TeV. Next we discuss some alternative new physics models which provide an effective ultraviolet cutoff lower than the Planck mass. An effective cutoff Λ?10¹¹ GeV$\Lambda ?{10}^{11}\text{GeV}$ leads to a vacuum stability bound on the Higgs mass of 125 GeV. In a gauge–Higgs unification scenario with five-dimensional flat spacetime, the so-called gauge–Higgs condition can yield a Higgs mass of 125 GeV, with the compactification scale of the extra-dimension being identified as the cutoff scale Λ?10¹¹ GeV$\Lambda ?{10}^{11}\text{GeV}$. Identifying the compactification scale with the unification scale of the SM SU(2) gauge coupling and the top quark Yukawa coupling yields a Higgs mass of 121±2 GeV$121\pm 2\text{GeV}$.     

Can charge drag explain the Pioneer anomaly?

According to precise measurements of Doppler shift for the signals from Pioneers 10 and 11, these two spacecraft have been experiencing a drag-like force of about 2×¹⁰⁻⁷ Newtons$2\times {10}^{\mathrm{-7}}\text{ Newtons}$ since they passed into the outer solar system. Recently, Nieto et al. [M.M. Nieto, et al., Phys. Lett. B 613 (2005) 11] have estimated the drag on these craft that would be caused by impacting dust grains in the region beyond 20 AU. They conclude that the amount of dust required to explain the anomaly is excessive, about 3×¹⁰⁻¹⁹ g/cc$3\times {10}^{\mathrm{-19}}\text{ g}/\text{cc}$. However, if the two spacecraft carry a large electric charge, then charge drag against the dusty plasma in this region could be significant. In the present Letter, estimates of this force are made, and conditions are found under which the observed level of drag is obtained. A density of charged dust of around 5×¹⁰⁻²² g/cc$5\times {10}^{\mathrm{-22}}\text{ g}/\text{cc}$ at a kinetic temperature of 10⁵ K suffices, provided that the dust grains are very small (mass ∼100 amu$\sim 100\text{ amu}$) and the spacecraft charge is near its reported maximum (Z∼¹⁰¹²$Z\sim {10}^{12}$).     

Minimal hypersurfaces in a nearly Kaehler 6-sphere

In this paper we show that for a compact minimal hypersurface M$M$ of constant scalar curvature in the unit sphere S⁶$S^6$ with the shape operator A$A$ satisfying ‖A‖²>5${\Vert A\Vert }^2>5$, there exists an eigenvalue λ>10$\lambda >10$ of the Laplace operator of the hypersurface M$M$ such that ‖A‖²=λ−5${\Vert A\Vert }^2=\lambda -5$. This gives the next discrete value of ‖A‖²${\Vert A\Vert }^2$ greater than 0 and 5.     

Atomic parity violation in the economical 3–3–1 model

The deviation δQW$\delta Q_{\mathrm{W}}$ of the weak charge from its standard model prediction due to the mixing of the W boson with the charged bilepton Y as well as of the Z   boson with the neutral Z^′$Z^{\prime }$ and the real part of the non-Hermitian neutral bilepton X   in the economical 3–3–1 model is established. Additional contributions to the usual δQW$\delta Q_{\mathrm{W}}$ expression in the extra U(1)$\mathrm{U}(1)$ models and the left–right models are obtained. Our calculations are quite different from previous analyzes in this kind of the 3–3–1 models and give the limit on mass of the Z^′$Z^{\prime }$ boson, the Z–Z^′$Z\text{–}{Z}^{\prime }$ and W–Y$W\text{–}Y$ mixing angles with the more appropriate values: MZ^′>564 GeV$M_{Z^{\prime }}>564\text{GeV}$, −0.018<sinφ<0$-0.018<\sin \phi <0$ and |sinθ|<0.043$|\sin \theta |<0.043$.     

Non-Hermitian perturbations to the Fritzsch textures of lepton and quark mass matrices

We show that non-Hermitian and nearest-neighbor-interacting perturbations to the Fritzsch textures of lepton and quark mass matrices can make both of them fit current experimental data very well. In particular, we obtain θ₂₃?45°${\theta }_{23}?45\text{°}$ for the atmospheric neutrino mixing angle and predict θ₁₃?3°${\theta }_{13}?3\text{°}$ to 6° for the smallest neutrino mixing angle when the perturbations in the lepton sector are at the 20% level. The same level of perturbations is required in the quark sector, where the Jarlskog invariant of CP violation is about 3.7×¹⁰⁻⁵$3.7\times {10}^{-5}$. In comparison, the strength of leptonic CP violation is possible to reach about 1.5×¹⁰⁻²$1.5\times {10}^{-2}$ in neutrino oscillations.     

Non-axisymmetric flexural vibrations of free-edge circular silicon wafers

Non-axisymmetric flexural vibrations of circular silicon (111) wafers are investigated. The modes with azimuthal index 2?k?30$2?k?30$ are electrostatically excited and monitored by a capacitive sensor. The splitting of the mode frequencies associated with imperfection of the wafer is observed. The measured loss factors for the modes with 6?k?26$6?k?26$ are close to those calculated according to the thermoelastic damping theory, while clamping losses likely dominate for k?6$k?6$, and surface losses at the level of inverse Q  -factor Q⁻¹≈4×10⁻⁶$Q^{-1}\approx 4\times {10}^{-6}$ prevail for the modes with large k. The modes demonstrate nonlinear behavior of mainly geometrical origin at large amplitudes.     

Spin-rotation coupling in compound spin objects

We generalize spin-rotation coupling to compound spin systems. In the case of muons bound to nuclei in a storage ring the decay process acquires a modulation. Typical frequencies for Z/A∼1/2$Z/A\sim 1/2$ are ∼3×10⁶ Hz$\sim 3\times {10}^6\text{Hz}$, a factor 10 higher than the modulation observed in g−2$g-2$ experiments.     

Nonlocal condensate model for QCD sum rules

We include effects of nonlocal quark condensates into QCD sum rules (QSR) via the Källén–Lehmann representation for a dressed fermion propagator, in which a negative spectral density function manifests their nonperturbative nature. Applying our formalism to the pion form factor as an example, QSR results are in good agreement with data for momentum transfer squared up to Q²≈10 GeV²$Q^2\approx 10{\text{GeV}}^2$. It is observed that the nonlocal quark condensate contribution descends like 1/Q²$1/Q^2$, different from the exponential decrease in Q²$Q^2$ obtained in the literature, and contrary to the linear rise in the local-condensate approximation.     

Quantum critical Hall exponents

We investigate a finite size “double scaling” hypothesis using data from an experiment on a quantum Hall system with short range disorder ,  and . For Hall bars of width w at temperature T   the scaling form is w^−μT^−κ$w^{-\mu }{T}^{-\kappa }$, where the critical exponent μ≈0.23$\mu \approx 0.23$ we extract from the data is comparable to the multi-fractal exponent _α0−2${\alpha }_0-2$ obtained from the Chalker–Coddington (CC) model [4]. We also use the data to find the approximate location (in the resistivity plane) of seven quantum critical points, all of which closely agree with the predictions derived long ago from the modular symmetry of a toroidal σ-model with m matter fields [5]. The value _ν8=2.60513…${\nu }_8=2.60513\dots$ of the localisation exponent obtained from the m=8$m=8$ model is in excellent agreement with the best available numerical value _νnum=2.607±0.004${\nu }_{\mathrm{num}}=2.607\pm 0.004$ derived from the CC-model [6]. Existing experimental data appear to favour the m=9$m=9$ model, suggesting that the quantum Hall system is not in the same universality class as the CC-model. We discuss the reason this may not be the case, and propose experimental tests to distinguish between the two possibilities.     

Probing a possible vacuum refractive index with γ-ray telescopes

We have used a stringy model of quantum space–time foam to suggest that the vacuum may exhibit a non-trivial refractive index depending linearly on γ  -ray energy: η−1∼Eγ/M_QG1$\eta -1\sim E_{\gamma }/M_{\mathrm{QG}1}$, where MQG$M_{\mathrm{QG}}$ is some mass scale typical of quantum gravity that may be ∼¹⁰¹⁸ GeV$\sim {10}^{18}\text{GeV}$: see [J. Ellis, N.E. Mavromatos, D.V. Nanopoulos, Phys. Lett. B 665 (2008) 412] and references therein. The MAGIC, HESS and Fermi γ-ray telescopes have recently probed the possible existence of such an energy-dependent vacuum refractive index. All find indications of time-lags for higher-energy photons, but cannot exclude the possibility that they are due to intrinsic delays at the sources. However, the MAGIC and HESS observations of time-lags in emissions from AGNs Mkn 501 and PKS 2155-304 are compatible with each other and a refractive index depending linearly on the γ  -ray energy, with M_QG1∼¹⁰¹⁸ GeV$M_{\mathrm{QG}1}\sim {10}^{18}\text{GeV}$. We combine their results to estimate the time-lag Δt   to be expected for the highest-energy photon from GRB 080916c measured by the Fermi telescope, which has an energy ∼13.2 GeV$\sim 13.2\text{GeV}$, assuming the redshift z=4.35±0.15$z=4.35\pm 0.15$ measured by GROND. In the case of a refractive index depending linearly on the γ  -ray energy we predict Δt=26±11 s$\mathrm{\Delta }t=26\pm 11\text{s}$. This is compatible with the time-lag Δt?16.5 s$\mathrm{\Delta }t?16.5\text{s}$ reported by the Fermi Collaboration, whereas the time-lag would be negligible in the case of a refractive index depending quadratically on the γ-ray energy. We suggest a strategy for future observations that could distinguish between a quantum-gravitational effect and other interpretations of the time-lags observed by the MAGIC, HESS and Fermi γ-ray telescopes.     

The size of the weak bosons

We study the hypothesis that the bosons are composite systems, which have a size of the order of 10⁻¹⁷ cm${10}^{-17}\text{cm}$. The electromagnetic self-energies of the weak bosons lead to specific departures from the standard elektroweak model, in agreement with observation. Above the energy of 1 TeV the standard electroweak model breaks down completely.