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.     

Eikonal contributions to ultra high energy neutrino–nucleon cross sections in low scale gravity models

We calculate low scale gravity effects on the cross section for neutrino–nucleon scattering at center of mass energies up to the Greisen–Zatsepin–Kuzmin (GZK) scale, in the eikonal approximation. We compare the cases of an infinitely thin brane embedded in n=5$n=5$ compactified extra-dimensions, and of a brane with a physical tension MS=1 TeV$M_S=1\text{TeV}$ and MS=10 TeV$M_S=10\text{TeV}$. The extra dimensional Planck scale MD$M_D$ is set at ¹⁰³ GeV${10}^3\text{GeV}$ and 2×¹⁰³ GeV$2\times {10}^3\text{GeV}$. We also compare our calculations with neutral current standard model calculations in the same energy range, and compare the thin brane eikonal cross section to its saddle point approximation. New physics effects enhance the cross section by orders of magnitude on average. They are quite sensitive to MS$M_S$ and MD$M_D$ choices, though much less sensitive to n.     

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$|\sin \theta |<0.043$.     

Search for lepton flavor violation in supersymmetric models via meson decays

Considering the constraints from the experimental data on μ→eγ$\mu \to e\gamma$, μ→3e$\mu \to 3e$, μ–e$\mu \text{–}e$ conversion, etc., we analyze the lepton flavor violating decays ?(J/Ψ,?(1S))→e⁺μ⁻(μ⁺τ⁻)$?(J/\Psi ,?(1S))\to e^{+}{\mu }^{-}({\mu }^{+}{\tau }^{-})$ in the scenarios of the minimal supersymmetric extensions of Standard Model with seesaw mechanism. Numerically, there is parameter space that the LFV processes of J/Ψ(?)→μ⁺τ⁻$J/\Psi (?)\to {\mu }^{+}{\tau }^{-}$ can reach the upper experimental bounds, meanwhile the theoretical predictions on μ→eγ$\mu \to e\gamma$, μ→3e$\mu \to 3e$, μ–e$\mu \text{–}e$ conversion satisfy the present experimental bounds. For searching of new physics, lepton flavor violating processes J/Ψ(?)→μ⁺τ⁻$J/\Psi (?)\to {\mu }^{+}{\tau }^{-}$ may be more promising and effective channels.     

Detecting Higgs bosons with muons at hadron colliders

We investigate the prospects for the discovery of neutral Higgs bosons with a pair of muons by direct searches at the CERN large hadron collider (LHC) as well as by indirect searches in the rare decay Bs→μ⁺μ⁻$B_s\to {\mu }^{+}{\mu }^{-}$ at the Fermilab Tevatron and the LHC. Promising results are found for the minimal supersymmetric standard model, the minimal supergravity (mSUGRA) model, and supergravity models with non-universal Higgs masses (NUHM SUGRA). For tanβ?50$\tan \beta ?50$, we find that (i) the contours for a branching fraction of B(Bs→μ⁺μ⁻)=1×¹⁰⁻⁸$B(B_s\to {\mu }^{+}{\mu }^{-})=1\times {10}^{\mathrm{-8}}$ in the parameter space are very close to the 5σ   contours for pp→b?⁰→bμ⁺μ⁻+X$pp\to b{?}^0\to b{\mu }^{+}{\mu }^{-}+X$, ?⁰=h⁰${?}^0=h^0$, H⁰$H^0$, A⁰$A^0$ at the LHC with an integrated luminosity (L) of 30 fb⁻¹, (ii) the regions covered by B(Bs→μ⁺μ⁻)?5×¹⁰⁻⁹$B(B_s\to {\mu }^{+}{\mu }^{-})?5\times {10}^{\mathrm{-9}}$ and the discovery region for b?⁰→bμ⁺μ⁻$b{?}^0\to b{\mu }^{+}{\mu }^{-}$ with 300 fb⁻¹ are complementary in the mSUGRA parameter space, (iii) in NUHM SUGRA models, a discovery of B(Bs→μ⁺μ⁻)?5×¹⁰⁻⁹$B(B_s\to {\mu }^{+}{\mu }^{-})?5\times {10}^{\mathrm{-9}}$ at the LHC will cover regions of the parameter space beyond the direct search for b?⁰→bμ⁺μ⁻$b{?}^0\to b{\mu }^{+}{\mu }^{-}$ with L=300 fb⁻¹$L=300{\text{fb}}^{\mathrm{-1}}$.     

Strange stars properties calculated in the framework of the Field Correlator Method

We calculate the strange star properties in the framework of the Field Correlator Method. We find that for gluon condensate values G₂$G_2$ in the range 0.006–0.007 GeV⁴$0.006\text{–}0.007{\text{GeV}}^4$, which give a critical temperature Tc∼170 MeV$T_c\sim 170\text{MeV}$ at μc=0${\mu }_c=0$, the sequences of strange stars are compatible with some of the semi-empirical mass–radius relations and data obtained from astrophysical observations.     

Chaotic inflation,radiative corrections and precision cosmology

We employ chaotic (?²${?}^2$ and ?⁴${?}^4$) inflation to illustrate the important role radiative corrections can play during the inflationary phase. Yukawa interactions of ?  , in particular, lead to corrections of the form −κ?⁴ln(?/μ)$-\kappa {?}^4\ln (?/\mu )$, where κ>0$\kappa >0$ and μ   is a renormalization scale. For instance, ?⁴${?}^4$ chaotic inflation with radiative corrections looks compatible with the most recent WMAP (5 year) analysis, in sharp contrast to the tree level case. We obtain the 95% confidence limits 2.4×¹⁰⁻¹⁴?κ?5.7×¹⁰⁻¹⁴$2.4\times {10}^{\mathrm{-14}}?\kappa ?5.7\times {10}^{\mathrm{-14}}$, 0.931?ns?0.958$0.931?n_s?0.958$ and 0.038?r?0.205$0.038?r?0.205$, where ns$n_s$ and r   respectively denote the scalar spectral index and scalar to tensor ratio. The limits for ?²${?}^2$ inflation are κ?7.7×¹⁰⁻¹⁵$\kappa ?7.7\times {10}^{\mathrm{-15}}$, 0.929?ns?0.966$0.929?n_s?0.966$ and 0.023?r?0.135$0.023?r?0.135$. The next round of precision experiments should provide a more stringent test of realistic chaotic ?²${?}^2$ and ?⁴${?}^4$ inflation.     

Probing the reheating temperature at colliders and with primordial nucleosynthesis

Considering gravitino dark matter scenarios with a long-lived charged slepton, we show that collider measurements of the slepton mass and its lifetime can probe not only the gravitino mass but also the post-inflationary reheating temperature TR$T_{\mathrm{R}}$. In a model independent way, we derive upper limits on TR$T_{\mathrm{R}}$ and discuss them in light of the constraints from the primordial catalysis of ⁶Li through bound-state effects. In the collider-friendly region of slepton masses below 1 TeV, the obtained conservative estimate of the maximum reheating temperature is about TR=3×¹⁰⁹ GeV$T_{\mathrm{R}}=3\times {10}^9\text{GeV}$ for the limiting case of a small gluino–slepton mass splitting and about TR=¹⁰⁸ GeV$T_{\mathrm{R}}={10}^8\text{GeV}$ for the case that is typical for universal soft supersymmetry breaking parameters at the scale of grand unification. We find that a determination of the gluino–slepton mass ratio at the Large Hadron Collider will test the possibility of TR>¹⁰⁹ GeV$T_{\mathrm{R}}>{10}^9\text{GeV}$ and thereby the viability of thermal leptogenesis with hierarchical heavy right-handed Majorana neutrinos.     

Effect of electric field of the electrosphere on photon emission from quark stars

We investigate the photon emission from the electrosphere of a quark star. It is shown that at temperatures T∼0.1–1 MeV$T\sim 0.1\text{–}1\text{MeV}$ the dominating mechanism is the bremsstrahlung due to bending of electron trajectories in the mean Coulomb field of the electrosphere. The radiated energy flux from this mechanism exceeds considerably both the contribution from the bremsstrahlung due to electron–electron interaction and the tunnel e⁺e⁻$e^{+}{e}^{-}$ pair creation.     

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.     

A simple explanation of the PVLAS anomaly in spontaneously broken mirror models

The PVLAS anomaly can be explained if there exist millicharged particles of mass ?0.1 eV$?0.1\text{eV}$ and electric charge ?∼¹⁰⁻⁶e$\mathrm{?}\sim {10}^{\mathrm{-6}}e$. We point out that such particles occur naturally in spontaneously broken mirror models. We argue that this interpretation of the PVLAS anomaly is not in conflict with astrophysical constraints due to the self interactions of the millicharged particles which lead them to be trapped within stars. This conclusion also holds for a generic paraphoton model.     

On search for eV hidden-sector photons in Super-Kamiokande and CAST experiments

If light hidden sector photons (γ^′${\gamma }^{\prime }$s) exist, they could be produced through kinetic mixing with solar photons in the eV energy range. We propose to search for this hypothetical γ^′${\gamma }^{\prime }$-flux with the Super-Kamiokande and/or upgraded CAST detectors. The proposed experiments are sensitive to the γ–γ^′$\gamma \text{–}{\gamma }^{\prime }$ mixing strength as small as ¹⁰⁻⁵?χ?¹⁰⁻⁹${10}^{\mathrm{-5}}?\chi ?{10}^{\mathrm{-9}}$ for the γ^′${\gamma }^{\prime }$ mass region ¹⁰⁻⁴?mγ^′?¹⁰⁻¹ eV${10}^{\mathrm{-4}}?m_{{\gamma }^{\prime }}?{10}^{\mathrm{-1}}\text{eV}$ and, in the case of non-observation, would improve limits recently obtained from photon regeneration laser experiments for this mass region.     

Pion radiative weak decays in nonlocal chiral quark models

We analyze the radiative pion decay π⁺→e⁺νeγ${\pi }^{+}\to e^{+}{\nu }_e\gamma$ within nonlocal chiral quark models that include wave function renormalization. In this framework we calculate the vector and axial-vector form factors FV$F_V$ and FA$F_A$ at q²=0$q^2=0$ — where q²$q^2$ is the e⁺νe$e^{+}{\nu }_e$ squared invariant mass — and the slope a   of FV(q²)$F_V(q^2)$ at q²→0$q^2\to 0$. The calculations are carried out considering different nonlocal form factors, in particular those taken from lattice QCD evaluations, showing a reasonable agreement with the corresponding experimental data. The comparison of our results with those obtained in the (local) NJL model and the relation of FV$F_V$ and a   with the form factor in π⁰→γ^?γ${\pi }^0\to {\gamma }^{?}\gamma$ decays are discussed.     

Kaon pair production close to threshold

The total cross section of the reaction pp→ppK⁺K⁻$pp\to pp{K}^{+}{K}^{-}$ has been measured at excess energies Q=10 MeV$Q=10\text{MeV}$ and 28 MeV with the magnetic spectrometer COSY-11. The new data show a significant enhancement of the total cross section compared to pure phase space expectations or calculations within a one boson exchange model. In addition, we present invariant mass spectra of two particle subsystems. While the K⁺K⁻$K^{+}{K}^{-}$ system is rather constant for different invariant masses, there is an enhancement in the pK⁻$p{K}^{-}$ system towards lower masses which could at least be partially connected to the influence of the Λ(1405)$\Lambda (1405)$ resonance.     

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.     

Cosmological constraints from radial baryon acoustic oscillation measurements and observational Hubble data

We use the Radial Baryon Acoustic Oscillation (RBAO) measurements, distant type Ia supernovae (SNe Ia), the observational H(z)$H(z)$ data (OHD) and the Cosmic Microwave Background (CMB) shift parameter data to constrain cosmological parameters of ΛCDM$\mathrm{\Lambda }\text{CDM}$ and XCDM cosmologies and further examine the role of OHD and SNe Ia data in cosmological constraints. We marginalize the likelihood function over h   by integrating the probability density P∝e−χ²/2$P\propto e^{-{\chi }^2/2}$ to obtain the best fitting results and the confidence regions in the Ωm–ΩΛ${\Omega }_m\text{–}{\Omega }_{\Lambda }$ plane. With the combination analysis for both of the ΛCDM$\mathrm{\Lambda }\text{CDM}$ and XCDM models, we find that the confidence regions of 68.3%, 95.4% and 99.7% levels using OHD+RBAO+CMB$\text{OHD}+\text{RBAO}+\text{CMB}$ data are in good agreement with that of SNe Ia+RBAO+CMB$\text{Ia}+\text{RBAO}+\text{CMB}$ data which is consistent with the result of Lin et al.'s (2009) [24] work. With more data of OHD, we can probably constrain the cosmological parameters using OHD data instead of SNe Ia data in the future.