We investigate a modification in the action of inflaton due to noncommutativity leads to a nonstandard initial vacuum and oscillatory corrections in the initial power spectrum. We show that the presence of these oscillations causes a drop in the WMAP ${\chi }^2$ about $\Delta {\chi }^2\sim 8.5$. As a bonus, from the parameter estimation done in this work, we show that the noncommutative parameters can be precisely bound to ${10}^{16}\mathrm{GeV}$ or ${10}^4\mathrm{GeV}$ depending on the inflation scale.

We show that the baryon asymmetry of the Universe can originate from the amplification of quantum fluctuations of a light complex scalar field during inflation. $CP$ violation is sourced by complex mass terms, which are smaller than the Hubble rate, as well as by nonstandard kinetic terms. We find that, when assuming 60 e-folds of inflation and charge conservation on superhorizon scales, a baryon asymmetry in accordance with observation can be produced in models where the energy scale of inflation is of the order of ${10}^{16}\mathrm{GeV}$. Baryogenesis can also be successful in lower scale inflationary models, provided inflationary epoch lasts sufficiently long.

A primordial magnetic field (PMF) can affect the evolution of density-field fluctuations in the early universe. In this paper we constrain the PMF amplitude $B_{\lambda }$ and power spectral index $n_{\mathrm{B}}$ by comparing calculated density-field fluctuations with observational data, i.e. the number density fluctuation of galaxies. We show that the observational constraints on cosmological density fluctuations, as parametrized by ${\sigma }_8$, lead to strong constraints on the amplitude and spectral index of the PMF.

The decay constants and the radiative decay widths of ${\eta }_b(nS)$ and ${\eta }_c(nS)$ are computed within a semirelativistic quark model, using a potential found through the AdS/QCD correspondence. For ${\eta }_c$, the results are in agreement with experimental data, while in the case of ${\eta }_c^{\prime }$ a discrepancy is found and the possible reasons are discussed.

A model has been proposed in which neutral scalar particles $\chi$, of mass 1–10 MeV, annihilate through the exchange of a light vector boson $U$, of mass 10–100 MeV, to produce the 511 keV line observed emanating from the center of the Galaxy. The $\chi$ interacts weakly with normal matter and is a viable dark matter candidate. If the $U$ boson couples to quarks as well as to electrons, it could enhance the branching ratio for the rare decay ${\pi }^0\to e^{+}{e}^{-}$. A recent measurement by the KTeV Collaboration lies 3 standard deviations above a prediction by Dorokhov and Ivanov, and we relate this excess to the couplings of the $U$ boson. The values are consistent with other constraints and considerations. We make some comments on possible improvements in the data.

We analyze the sigma meson mass and width together with the pion-pion scattering parameters in the context of nonlocal chiral quark models with wave function renormalization (WFR). We consider both nonlocal interactions based on the frequently used exponential form factor, and on fits to the quark mass and renormalization functions obtained in lattice calculations. In the case of the sigma properties, we obtain results which are less dependent on the parametrization than in the standard local Nambu-Jona-Lasinio model, and which are in reasonable agreement with the recently reported empirical values. We also show that the inclusion of the WFR tend to improve the description of the $\pi \mathrm{\text{−}}\pi$ scattering parameters, with the lattice inspired parametrization providing the best overall results. Finally, we analyze the connection of the nonlocal quark models discussed here with chiral perturbation theory, and present the model predictions for the low-energy constants relevant for $\pi \mathrm{\text{−}}\pi$ scattering to $O(4)$ in the chiral expansion.

We explore how the seesaw sector in neutrino mass models may be constrained through symmetries to be completely determined in terms of low-energy mass, mixing angle and $CP$-violating phase observables. The key ingredients are intrafamily symmetries to determine the neutrino Dirac mass matrix in terms of the charged-lepton or quark mass matrices, together with interfamily or flavor symmetries to determine diagonalization matrices. Implications for leptogenesis and collider detection of heavy neutral leptons are discussed. We show that leptogenesis can succeed in small regions of parameter space for the case where the neutrino Dirac mass matrix equals the up-quark mass matrix. The model where the neutrino Dirac mass matrix equals the charged-lepton mass matrix can yield a heavy neutral lepton as light as about 1 TeV, but detecting such a particle will be difficult.

The properties of the dark matter that determine its thermal relic abundance can be very different from the dark matter properties today. We investigate this possibility by coupling a dark matter sector to a scalar that undergoes a phase transition after the dark matter freezes out. If the value of ${\Omega }_{\mathrm{DM}}{h}^2$ calculated from parameters measured at colliders and by direct and indirect detection experiments does not match the astrophysically observed value, a novel cosmology of this type could provide the explanation.

We present the first measurement of $\sigma (gg\to t\overline{t})/\sigma (p\overline{p}\to t\overline{t})$. We use $0.96{\mathrm{fb}}^{-1}$ of $\sqrt{s}=1.96\mathrm{TeV}$ $p\overline{p}$ collision data recorded with the CDF II detector at Fermilab. Using charged particles with low transverse momentum in $t\overline{t}$ events, we find $\sigma (gg\to t\overline{t})/\sigma (p\overline{p}\to t\overline{t})=0.07\pm 0.14(\mathrm{stat})\pm 0.07(\mathrm{syst})$, corresponding to a 95% confidence level upper limit of 0.33, in agreement with the standard model next-to-leading-order prediction of $0.15\pm 0.05$.

It is shown that the primary proton spectrum, reconstructed from sea-level and underground data on muon spectrum with the use of QGSJET 01, QGSJET II, NEXUS 3.97, and SIBYLL 2.1 interaction models, demonstrates not only model-dependent intensity, but also a model-dependent form. For correct reproduction of muon spectrum shape the primary proton flux should have a nonconstant power index for all considered models, except SIBYLL 2.1, with break at energies around 10–15 TeV and a value of exponent before break close to that obtained in the ATIC-2 experiment. To validate the presence of this break, understanding of inclusive spectra behavior in the fragmentation region in $p$-air collisions should be improved, but we show that is impossible to do on the basis of the existing experimental data on primary nuclei, atmospheric muon, and hadron fluxes.

The next-to-minimal supersymmetric standard model (NMSSM) with a large $\lambda$ (the mixing parameter between the singlet and doublet Higgs fields) is well motivated since it can significantly push up the upper bound on the standard model-like Higgs boson mass to solve the little hierarchy problem. In this work we examine the current experimental constraints on the NMSSM with a large $\lambda$, which include the direct search for Higgs bosons and sparticles at colliders, the indirect constraints from precision electroweak measurements, the cosmic dark matter relic density, the muon anomalous magnetic moment, as well as the stability of the Higgs potential. We find that, with the increase of $\lambda$, parameters like $\tan \beta$, $M_A$, $\mu$, and $M_2$ are becoming more stringently constrained. It turns out that the maximal reach of $\lambda$ is limited by the muon anomalous magnetic moment, and for smuon masses of 200 GeV (500 GeV) the parameter space with $\lambda \gtrsim 1.5(0.6)$ is excluded.

We calculate the branching ratios and $CP$-violating asymmetries of the four $B\to K{\eta }^{(\prime )}$ decays in the perturbative QCD (pQCD) factorization approach. Besides the full leading-order contributions, the partial next-to-leading-order (NLO) contributions from the QCD vertex corrections, the quark-loops, and the chromomagnetic penguins are also taken into account. The NLO pQCD predictions for the $CP$-averaged branching ratios are $\mathrm{Br}(B^{+}\to K^{+}\eta )\approx 3.2\times {10}^{-6}$, $\mathrm{Br}(B^{\pm }\to K^{\pm }{\eta }^{\prime })\approx 51.0\times {10}^{-6}$, $\mathrm{Br}(B^0\to K^0\eta )\approx 2.1\times {10}^{-6}$, and $\mathrm{Br}(B^0\to K^0{\eta }^{\prime })\approx 50.3\times {10}^{-6}$. The NLO contributions can provide a 70% enhancement to the LO $\mathrm{Br}(B\to K{\eta }^{\prime })$, but a 30% reduction to the LO $\mathrm{Br}(B\to K\eta )$, which play the key role in understanding the observed pattern of branching ratios. The NLO pQCD predictions for the $CP$-violating asymmetries, such as ${\mathcal{A}}_{CP}^{\mathrm{dir}}(K_S^0{\eta }^{\prime })\sim 2.3\%$ and ${\mathcal{A}}_{CP}^{\mathrm{mix}}(K_S^0{\eta }^{\prime })\sim 63\%$, agree very well with currently available data. This means that the deviation $\Delta S={\mathcal{A}}_{CP}^{\mathrm{mix}}(K_S^0{\eta }^{\prime })-\sin 2\beta$ in pQCD approach is also very small.

We present branching fraction measurements for the radiative decays $B^{+}\to {\rho }^{+}\gamma$, $B^0\to {\rho }^0\gamma$, and $B^0\to \omega \gamma$. The analysis is based on a data sample of $465\times {10}^6$ $B\overline{B}$ events collected with the BABAR detector at the PEP-II asymmetric-energy $B$ Factory located at the Stanford Linear Accelerator Center. We find $\mathcal{B}(B^{+}\to {\rho }^{+}\gamma )=({1.20}_{-0.37}^{+0.42}\pm 0.20)\times {10}^{-6}$, $\mathcal{B}(B^0\to {\rho }^0\gamma )=({0.97}_{-0.22}^{+0.24}\pm 0.06)\times {10}^{-6}$, and a 90% C.L. upper limit $\mathcal{B}(B^0\to \omega \gamma )<0.9\times {10}^{-6}$, where the first error is statistical and the second is systematic. We also measure the isospin-violating quantity $\Gamma (B^{+}\to {\rho }^{+}\gamma )/2\Gamma (B^0\to {\rho }^0\gamma )-1=-{0.43}_{-0.22}^{+0.25}\pm 0.10$.

We use the leading singularity technique to determine the planar six-particle two-loop maximally helicity violating amplitude in $\mathcal{N}=4$ super Yang-Mills theory in terms of a simple basis of integrals. Our result for the parity-even part of the amplitude agrees with the one recently presented in [1]. The parity-odd part of the amplitude is a new result. The leading singularity technique reduces the determination of the amplitude to finding the solution to a system of linear equations. The system of equations is easily found by computing residues. We present the complete system of equations, which determines the whole amplitude, and solve the two-by-two blocks analytically. Larger blocks are solved numerically in order to test the Anastasiou Bern Dixon Kosower/Bern Dixon Smirnov iterative structure.

The vacuum expectation values of the energy-momentum tensor and the fermionic condensate are analyzed for a massive spinor field obeying the MIT bag boundary condition on a cylindrical shell in the cosmic string spacetime. Both regions inside and outside the shell are considered. By applying to the corresponding mode sums a variant of the generalized Abel-Plana formula, we explicitly extract the parts in the expectation values corresponding to the cosmic string geometry without boundaries. In this way the renormalization procedure is reduced to that for the boundary-free cosmic string spacetime. The parts induced by the cylindrical shell are presented in terms of integrals rapidly convergent for points away from the boundary. The behavior of the vacuum densities is investigated in various asymptotic regions of the parameters. In the limit of large values of the planar angle deficit, the boundary-induced expectation values are exponentially suppressed. As a special case, we discuss the fermionic vacuum densities for the cylindrical shell on the background of the Minkowski spacetime.

It is observed that three-dimensional Gödel black holes can be promoted to exact string theory backgrounds through an orbifold of a hyperbolic asymmetric marginal deformation of the $\mathrm{SL}(2,\mathbb{R})$ Wess-Zumino-Witten model. Tachyons are found in the spectrum of long strings. Uplifting these solutions in type IIB supergravity, extremal black holes are shown to preserve one supersymmetry in accordance with the Bañados-Teitelboim-Zanelli limit. We also make connections with some recently discussed warped black hole solutions of topologically massive gravity.

The clustering properties of sterile neutrinos are studied within a simple extension of the minimal standard model, where these neutrinos are produced via the decay of a gauge singlet scalar. The distribution function after decoupling is strongly out of equilibrium and features an enhancement at small comoving momentum $\propto 1/\sqrt{p}$. Dark matter abundance and phase space density constraints from dwarf spheroidal galaxies constrain the mass in the keV range consistent with a Yukawa coupling to a gauge singlet with mass and vacuum expectation value in the range $\sim 100\mathrm{GeV}$ and a decoupling temperature of this order. The dark matter transfer function and power spectrum are obtained from the solution of the nonrelativistic Boltzmann-Vlasov equation in the matter dominated era. The small momentum enhancement of the nonequilibrium distribution function leads to long range memory of gravitational clustering and a substantial enhancement of the power spectrum at small scales as compared to a thermal relic or sterile neutrino produced via nonresonant mixing with active neutrinos. The scale of suppression of the power spectrum for a sterile neutrino with $m\sim \mathrm{keV}$ produced by scalar decay that decouples at $\sim 100\mathrm{GeV}$ is $\lambda \sim 488\mathrm{kpc}$. At large scales $T(k)\sim 1-C{k}^2/k_{\mathrm{fs}}^2(t_{\mathrm{eq}})+\cdots$ with $C\sim \mathrm{O}(1)$. At small scales $65\mathrm{kpc}\lesssim \lambda \lesssim 500\mathrm{kpc}$ corrections to the fluid description and memory of gravitational clustering become important, and we find $T(k)\simeq 1.902e^{-k/k_{\mathrm{fs}}(t_{\mathrm{eq}})}$, where $k_{\mathrm{fs}}(t_{\mathrm{eq}})\sim 0.013/\mathrm{kpc}$ is the free-streaming wave vector at matter-radiation equality. The enhancement of power at small scales may provide possible relief to the tension between the constraints from x-ray and Lyman-$\alpha$ forest data.

We study the reduction of the (bosonic) string sigma model on an ${\mathrm{AdS}}_4\times {\mathbb{C}\mathbb{P}}^3$ background. We give a brief review of the known results for the AdS part and apply an explicit reduction scheme to the ${\mathbb{C}\mathbb{P}}^3$ part of the model. A brief discussion on the reduced model is presented.

This paper describes an application of the Mathisson-Papapetrou-Dixon (MPD) equations in analytic perturbation form to the case of circular motion around a radially accreting or radiating black hole described by the Vaidya metric. Based on the formalism presented earlier, this paper explores the effects of mass accretion or loss of the central body on the overall dynamics of the orbiting spinning particle. This includes changes to its squared mass and spin magnitude due to the classical analog of radiative corrections from spin-curvature coupling. Various quantitative consequences are explored when considering orbital motion near the black hole’s event horizon. An analysis on the orbital stability properties due to spin-curvature interactions is examined briefly, with conclusions in general agreement with previous work performed for the case of circular motion around a Kerr black hole.

This paper presents an analytic perturbation approach to the dynamics of a classical spinning particle, according to the Mathisson-Papapetrou-Dixon (MPD) equations of motion, with a direct application to circular motion around a Kerr black hole. The formalism is established in terms of a power series expansion with respect to the particle’s spin magnitude, where the particle’s kinematic and dynamical degrees are expressed in a completely general form that can be constructed to infinite order in the expansion parameter. It is further shown that the particle’s squared mass and spin magnitude can shift due to a classical analogue of radiative corrections that arise from spin-curvature coupling. Explicit expressions are determined for the case of circular motion near the event horizon a Kerr black hole, where the mass and spin shift contributions are dependent on the initial conditions of the particle’s spin orientation. A preliminary analysis of the stability properties of the orbital motion in the Kerr background due to spin-curvature interactions is explored and briefly discussed.