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.     

Phonon energy inversion in graphene during transient thermal transport

This work reports on the phonon energy inversion in graphene nanoribbons: after initial localized thermal excitation, the energy of initial cold phonons (flexural mode: FM) becomes higher than that of local hot phonons (longitudinal and transverse modes: LM/TM). Such energy inversion holds for about 50 picoseconds. Two physical factors combine together to give rise of this phenomenon: one is the much faster heat conduction by FM phonons than that by LM/TM phonons, and the other factor is the strongly temperature-dependent energy exchange rate between FM and LM/TM phonons: 3.7×10¹⁰ s⁻¹$3.7\times {10}^{10}{\text{s}}^{-1}$ at 84 K to 20.3×10¹⁰ s⁻¹$20.3\times {10}^{10}{\text{s}}^{-1}$ at around 510 K.     

The MD simulation of thermal properties of plutonium dioxide

The thermodynamic properties of PuO₂ have been investigated between 300 and 3000 K by molecular dynamics (MD) simulation with empirical interaction potential. The properties include melting point, lattice parameter variation, enthalpy and heat capacity. The melting point of two-phase simulation (TPS) is in agreement with the experimental value, and it gives a much lower value than one-phase simulation (OPS). The lattice parameter and heat capacity at high temperatures are expressed as a(T)=5.38178+4.38×10⁻⁵T+6.5525×10⁻⁹T²+0.9362×10⁻¹²T³$a(\mathrm{T})=5.38178+4.38\times 10^{-5}T+6.5525\times 10^{-9}{T}^2+0.9362\times 10^{-12}{T}^3$ and C_P(KJ⋅mol⁻¹⋅K⁻¹)=18648.8e^474.5/T/(T²(e^474.5/T−1)²)+9.337×10⁻⁶T$C_P(\mathrm{KJ}\cdot {\mathrm{mol}}^{-1}\cdot {\mathrm{K}}^{-1})=18648.8e^{474.5/T}/(T^2{(e^{474.5/T}-1)}^2)+9.337\times {10}^{-6}T$, respectively. True linear thermal expansion coefficient (TLTEC) α is about 8.89×10⁻⁶ K⁻¹ at 300 K. Our simulation results are in good agreement with experimental and other theoretical data.     

Constraints on sub-GeV hidden sector gauge bosons from a search for heavy neutrino decays

Several models of dark matter motivate the concept of hidden sectors consisting of SU_(3)C×SU_(2)L×U_(1)Y$\mathit{SU}{(3)}_C\times \mathit{SU}{(2)}_L\times U{(1)}_Y$ singlet fields. The interaction between our and hidden matter could be transmitted by new abelian U^′(1)$U^{\prime }(1)$ gauge bosons A^′$A^{\prime }$ mixing with ordinary photons. If such A^′$A^{\prime }$?s with the mass in the sub-GeV range exist, they would be produced through mixing with photons emitted in decays of η   and η^′${\eta }^{\prime }$ neutral mesons generated by the high energy proton beam in a neutrino target. The A^′$A^{\prime }$?s would then penetrate the downstream shielding and be observed in a neutrino detector via their A^′→e⁺e⁻$A^{\prime }\to e^{+}{e}^{-}$ decays. Using bounds from the CHARM neutrino experiment at CERN that searched for an excess of e⁺e⁻$e^{+}{e}^{-}$ pairs from heavy neutrino decays, the area excluding the γ−A^′$\gamma -A^{\prime }$ mixing range 10⁻⁷???10⁻⁴${10}^{-7}???{10}^{-4}$ for the A^′$A^{\prime }$ mass region 1?_MA′?500 MeV$1?M_{A^{\prime }}?500\text{MeV}$ is derived. The obtained results are also used to constrain models, where a new gauge boson X   interacts with quarks and leptons. New upper limits on the branching ratio as small as Br(η→γX)?10⁻¹⁴$\mathrm{Br}(\eta \to \gamma X)?{10}^{-14}$ and Br(η^′→γX)?10⁻¹²$\mathrm{Br}({\eta }^{\prime }\to \gamma X)?{10}^{-12}$ are obtained, which are several orders of magnitude more restrictive than the previous bounds from the Crystal Barrel experiment.     

Evidence for a negative-parity spin-doublet of nucleon resonances at 1.88 GeV

Evidence is reported for two nucleon resonances with spin-parity J^P=1/2⁻$J^P=1/2^{-}$ and J^P=3/2⁻$J^P=3/2^{-}$ at a mass just below 1.9 GeV. The evidence is derived from a coupled-channel analysis of a large number of pion and photo-produced reactions. The two resonances are nearly degenerate in mass with two resonances of the same spin but positive parity. Such parity doublets are predicted in models claiming restoration of chiral symmetry in high-mass excitations of the nucleon. Further examples of spin parity doublets are found in addition. Alternatively, the spin doublet can be interpreted as member of the 56-plet expected in the third excitation band of the nucleon. Implications for the problem of the missing resonances are discussed.     

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.     

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.     

Odderon and pomeron from the vacuum correlator method

Glueball masses with J?7$J?7$ are computed both for C=+1$C=+1$ and C=−1$C=-1$ using the string Hamiltonian derived in the framework of the vacuum correlator method. No fitting parameters are used, and masses are expressed in terms of string tension σ   and effective value of αs${\alpha }_s$. We extend the calculations done for J?3$J?3$ using the same Hamiltonian, which provided glueball masses in good agreement with existing lattice data, to higher mass states. It is shown that ³⁻⁻,⁵⁻⁻$3^{--},5^{--}$ and ⁷⁻⁻$7^{--}$ states lie on the odderon trajectories with the intercept around or below 0.14. Another odderon trajectory with 3g glueballs of Y-shape, corresponds to 11% higher masses and low intercept. These findings are in agreement with recent experimental data, setting limits on the odderon contribution to the exclusive γp reactions.     

The effect of initial spatial correlations on late time kinetics of bimolecular irreversible reactions

We study anomalous kinetics associated with incomplete mixing for a bimolecular irreversible kinetic reaction where the underlying transport of reactants is governed by a fractional dispersion equation. As has been previously shown, we demonstrate that at late times incomplete mixing effects dominate and the decay of reactants follows a fundamentally different scaling comparing to the idealized well mixed case. We do so in a fully analytical manner using moment equations. In particular the novel aspect of this work is that we focus on the role that the initial correlation structure of the distribution of reactants plays on the late time scalings. We focus on short range and long (power law) range correlations and demonstrate how long range correlations can give rise to different late time scalings than one would expect purely from the underlying transport model. For the short range correlations the late time scalings deviate from the well mixed t⁻¹$t^{-1}$ and scale like t^−1/2α$t^{-1/2\alpha }$, where 1<α≤2$1<\alpha \le 2$ is the fractional dispersion exponent, in agreement with previous studies. For the long range correlation case it scales like t^−β/2α$t^{-\beta /2\alpha }$, where 0<β<1$0<\beta <1$ is the power law correlation exponent.     

Dark matter annihilation in the Galactic Center as seen by the Fermi Gamma Ray Space Telescope

We analyze the first two years of data from the Fermi Gamma Ray Space Telescope from the direction of the inner 10° around the Galactic Center with the intention of constraining, or finding evidence of, annihilating dark matter. We find that the morphology and spectrum of the emission between 1.25° and 10° from the Galactic Center is well described by the processes of decaying pions produced in cosmic ray collisions with gas, and the inverse Compton scattering of cosmic ray electrons in both the disk and bulge of the Inner Galaxy, along with gamma rays from known points sources in the region. The observed spectrum and morphology of the emission within approximately 1.25° (∼175 parsecs) of the Galactic Center, in contrast, departs from the expectations for by these processes. Instead, we find an additional component of gamma ray emission that is highly concentrated around the Galactic Center. The observed morphology of this component is consistent with that predicted from annihilating dark matter with a cusped (and possibly adiabatically contracted) halo distribution (ρ∝r−γ$\rho \propto r^{-\gamma }$, with γ=1.18$\gamma =1.18$ to 1.33). The observed spectrum of this component, which peaks at energies between 1–4 GeV (in E²$E^2$ units), can be well fit by a 7–10 GeV dark matter particle annihilating primarily to tau leptons with a cross section in the range of 〈σv〉=4.6×¹⁰⁻²⁷$〈\sigma v〉=4.6\times {10}^{-27}$ to 5.3×¹⁰⁻²⁶ cm³/s$5.3\times {10}^{-26}{\text{cm}}^3/\text{s}$, depending on how the dark matter distribution is normalized. We also discuss other sources for this emission, including the possibility that much of it originates from the Milky Way?s supermassive black hole.     

New insights into the neutron electric dipole moment

We analyze the CP-violating electric dipole form factor of the nucleon in the framework of covariant baryon chiral perturbation theory. We give a new upper bound on the vacuum angle, |θ₀|?2.5×¹⁰⁻¹⁰$|{\theta }_0|?2.5\times {10}^{-10}$. The quark mass dependence of the electric dipole moment is discussed and compared to lattice QCD data. We also perform the matching between its representations in the three- and two-flavor theories.     

Dilaton field and cosmic wave propagation

We study the electromagnetic wave propagation in the joint dilaton field and axion field. Dilaton field induces amplification/attenuation in the propagation while axion field induces polarization rotation. The amplification/attenuation induced by dilaton is independent of the frequency (energy) and the polarization of electromagnetic waves (photons). From observations, the agreement with and the precise calibration of the cosmic microwave background (CMB) to blackbody radiation constrains the fractional change of dilaton |Δψ|/ψ$|\mathrm{\Delta }\psi |/\psi$ to less than about 8×10⁻⁴$8\times {10}^{-4}$ since the time of the last scattering surface of the CMB.     

High substitution of Fe for Zr in ZrV1.6P0.4O7 with small amount of FeV0.8P0.2O4 for low thermal expansion

Fe³⁺-doped ZrV_1.6P_0.4O₇ with Fe:Zr molar ratios of 1:9, 2:8, 3:7 and 4:6 was synthesized to reduce phase transition and obtain low thermal expansion. It is shown that the phase transition temperature of Fe-doped ZrV_1.6P_0.4O₇ is reduced obviously with increasing the content of Fe. Fe³⁺ ion with lower valence and smaller radius than that of Zr⁴⁺ favors to extend the bond angle of V–O–V(P) close to 180° in ZrV_1.6P_0.4O₇, which is considered responsible for the normal structure at room temperature and low thermal expansion. The thermal expansion coefficients of Fe-doped ZrV_1.6P_0.4O₇ for Fe:Zr molar ratios from 1:9 to 4:6 are calculated to be from −4.33×10⁻⁶$-4.33\times {10}^{-6}$ to 5.2×10⁻⁷ K⁻¹$5.2\times {10}^{-7}{\text{K}}^{-1}$ by linear thermal expansion measurement. The effect of small amount of FeV_0.8P_0.2O₄ formation with higher content of Fe³⁺ on thermal expansion coefficients of the samples is discussed.     

Implications of mirror dark matter kinetic mixing for CMB anisotropies

Mirror dark matter is a dissipative and self-interacting multiparticle dark matter candidate which can explain the DAMA, CoGeNT and CRESST-II direct detection experiments. This explanation requires photon–mirror photon kinetic mixing of strength ?∼10⁻⁹$?\sim {10}^{-9}$. Mirror dark matter with such kinetic mixing can potentially leave distinctive signatures on the CMB anisotropy spectrum. We show that the most important effect of kinetic mixing on the CMB anisotropies is the suppression of the height of the third and higher odd peaks. If ??10⁻⁹$??{10}^{-9}$ then this feature can be observed by the PLANCK mission in the near future.