Nonzero masses for the active neutrinos—regardless of their nature or origin—arise only after electroweak symmetry breaking. We discuss the parameterization of neutrino couplings to a Higgs sector consisting of one $SU(2{)}_L$ scalar doublet and one $SU(2{)}_L$ scalar triplet, and allow for right-handed neutrinos whose Majorana mass parameters arise from the vacuum expectation value of a standard model scalar singlet. If the neutrinos are Majorana fermions, all Yukawa couplings can be expressed as functions of the neutrino mass eigenvalues and a subset of the elements of the neutrino mixing matrix. In the mass basis, the Yukawa couplings are, in general, not diagonal. This is to be contrasted to the case of charged fermions or Dirac neutrinos, where couplings to the Higgs-boson are diagonal in the mass basis and proportional only to the fermion masses. Nonetheless, all physically distinguishable parameters can be reached if all neutrino masses are constrained to be positive, all mixing angles constrained to lie in the first quadrant ($\theta \in [0,\pi /2]$), and all Majorana phases to lie in the first two quadrants ($\varphi \in [0,\pi \}$), as long as all Dirac phases vary within the entire unit circle ($\delta \in [0,2\pi \}$). We discuss several concrete examples and comment on the Casas-Ibarra parameterization for the neutrino Yukawa couplings in the case of the type I seesaw Lagrangian. We also comment on the case where $SU(2{)}_L$ fermion triplets replace the right-handed neutrinos.

The hadron loop effect is conjectured to be important in understanding discrepancies between the observed states in experiments and the theoretical expectations of the nonrelativistic potential model. We present that in an easily operable procedure the hadron loop effect could shift the poles downwards to reduce the differences and provide better descriptions of both the masses and the total widths, at least, of the radial quantum number $n=1$ charmed and charmed-strange states. The $1^1{P}_1-1^3{P}_1$ mixing phenomena could be naturally explained due to their couplings with common channels. The newly observed $D$ states are also addressed, but there are still some problems that remain unclear.

We analytically calculate the cross sections of double charmonium production in $e^{+}{e}^{-}\to J/\psi (\psi (2S)){\chi }_{cJ}$ ($J=0$, 1, 2) at next-to-leading order (NLO) in ${\alpha }_s$ in nonrelativistic QCD, and confirm factorization of these processes. In contrast to ${\chi }_{c0}$ production, for which the NLO correction is large and positive, the NLO corrections for ${\chi }_{c1,2}$ production can be negative, resulting in decreased $K$ factors of 0.91 and 0.78 for $J=1$ and 2, respectively, when $\mu =2m_c$. Consequently, the NLO QCD corrections markedly enlarge the difference between cross sections of ${\chi }_{c0}$ and ${\chi }_{c1,2}$. This may explain why $e^{+}{e}^{-}\to J/\psi (\psi (2S)){\chi }_{c0}$ but not $e^{+}{e}^{-}\to J/\psi (\psi (2S)){\chi }_{c1,2}$ is observed experimentally. Moreover, for $J/\psi (\psi (2S)){\chi }_{c1,2}$, the NLO QCD corrections substantially reduce the $\mu$ dependence and lead to predictions with small theoretical uncertainties.

The recent discoveries of the bottomonia states $h_b(1P)$ and $h_b(2P)$ confirm the quark model prediction, already verified in the charmonia sector, that the hyperfine splitting of $P$-wave mesons is very small. The striking agreement is somewhat surprising because the nonrelativistic result, for which the splitting is zero, may be modified due to large mass shifts from coupling to open flavour meson pairs. This paper is based on the observation that in most models hyperfine splitting remains small, despite what are in many cases large mass shifts. This effect is shown to be a generic feature of models in which the coupling is driven by the creation of a light quark pair with spin-one.

Using a sample of $(225.2\pm 2.8)\times {10}^6$ $J/\psi$ events collected with the Beijing Spectrometer at the Beijing Electron-Positron Collider, $CP$ and $P$ violating decays of $\eta$, ${\eta }^{\prime }$, and ${\eta }_c$ into ${\pi }^{+}{\pi }^{-}$ and ${\pi }^0{\pi }^0$ are searched for in $J/\psi$ radiative decays. No significant $\eta$, ${\eta }^{\prime }$, or ${\eta }_c$ signal is observed, and $90\%$ confidence level upper limits of $\mathcal{B}(\eta \to {\pi }^{+}{\pi }^{-})<3.9\times {10}^{-4}$, $\mathcal{B}({\eta }^{\prime }\to {\pi }^{+}{\pi }^{-})<5.5\times {10}^{-5}$, $\mathcal{B}({\eta }_c\to {\pi }^{+}{\pi }^{-})<1.3\times {10}^{-4}$, $\mathcal{B}(\eta \to {\pi }^0{\pi }^0)<6.9\times {10}^{-4}$, $\mathcal{B}({\eta }^{\prime }\to {\pi }^0{\pi }^0)<4.5\times {10}^{-4}$, and $\mathcal{B}({\eta }_c\to {\pi }^0{\pi }^0)<4.2\times {10}^{-5}$ are obtained.

We present a Lagrangian describing a massive charged spin-2 field and a scalar in a constant electromagnetic background, and we provide a consistent description of the system. The Lagrangian, derived from string field theory through a suitable dimensional reduction, propagates the correct number of degrees of freedom within the light cone in any space-time dimension less than 26. We briefly discuss the higher-spin generalization of this construction, that cures the pathologies of a massive charged particle of arbitrary integer spin by introducing only finitely many new massive degrees of freedom.

In this paper, we obtain a new solution of a brane made up of a scalar field coupled to a dilaton. There is a unique parameter $b$ in the solution, which decides the distribution of the energy density and will affect the localization of bulk matter fields. For free vector fields, we find that the zero mode can be localized on the brane. And for vector fields coupled with the dilaton via ${\mathrm{e}}^{\tau \pi }{F}_{MN}{F}^{MN}$, the condition for localizing the zero mode is $\tau \ge -\sqrt{b/3}$ with $0<b\le 1$, or $\tau >-1/\sqrt{3b}$ with $b>1$, which includes the case $\tau =0$. While the zero mode for free Kalb-Ramond fields cannot be localized on the brane, if only we introduce a coupling between the Kalb-Ramond fields and the dilaton via ${\mathrm{e}}^{\zeta \pi }{H}_{MNL}{H}^{MNL}$. When the coupling constant satisfies $\zeta >1/\sqrt{3b}$ with $b\ge 1$ or $\zeta >\frac{2-b}{\sqrt{3b}}$ with $0<b<1$, the zero mode for the KR fields can be localized on the brane. For spin half fermion fields, we consider the coupling $\eta \overline{\Psi }{\mathrm{e}}^{\lambda \pi }\varphi \Psi$ between the fermions and the background scalars with positive Yukawa coupling $\eta$. The effective potentials for both chiral fermions have three types of shapes decided by the relation between the dilaton-fermion coupling constant $\lambda$ and the parameter $b$. For $\lambda \le -1/\sqrt{3b}$, the zero mode of left-chiral fermion can be localized on the brane. While for $\lambda >-1/\sqrt{3b}$ with $b>1$ or $-1/\sqrt{3b}<\lambda <-\sqrt{b/3}$ with $0<b\le 1$, the zero mode for left-chiral fermion also can be localized.

Vacuum-to-vacuum instantonic transitions modify the power spectrum of primordial gravitational waves. We evaluate the new form of the power spectrum for ordinary gravity as well as the parity violation induced in the spectrum by a modification of general relativity known as the Holst term and we outline the possible experimental consequences.

We investigate Choptuik scaling in the spherically symmetric collapse of a massless scalar field in higher dimensions using Painleve-Gullstrand coordinates. Our analysis gives reliable results for the critical exponent and period echoing up to seven dimensions and confirms the presence in higher dimensions of the cusps in the periodic scaling relationship recently observed in four dimensional collapse. In addition, our value for the critical exponent in seven dimensions is consistent with that obtained by Bland et al., who argued that the critical exponent increases monotonically with dimension to an asymptotic value of $1/2$.

In this paper, we investigate the localization and the mass spectra of gravity and various bulk matter fields on a thick anti–de Sitter (AdS) brane, by presenting the mass-independent potentials of the Kaluza-Klein (KK) modes in the corresponding Schrödinger equations. For gravity, the potential of the KK modes tends to infinity at the boundaries of the extra dimension, which leads to an infinite number of the bound KK modes. Although the gravity zero mode cannot be localized on the AdS brane, the massive modes are trapped on the brane. The scalar perturbations of the thick AdS brane have been analyzed, and the brane is stable under the scalar perturbations. For spin-0 scalar fields and spin-1 vector fields, the potentials of the KK modes also tend to infinity at the boundaries of the extra dimension, and the characteristic of the localization is the same as the case of gravity. For spin-1/2 fermions, by introducing the usual Yukawa coupling $\eta \overline{\Psi }\varphi \Psi$ with the positive coupling constant $\eta$, the four-dimensional massless left-chiral fermion and massive Dirac fermions are obtained on the AdS thick brane.

We relate the observable number of sources per solid angle and redshift to the underlying proper source density and velocity, background evolution, and line-of-sight potentials. We give an exact result in the case of linearized perturbations assuming general relativity. This consistently includes contributions of the source density perturbations and redshift distortions, magnification, radial displacement, and various additional linear terms that are small on subhorizon scales. In addition, we calculate the effect on observed luminosities and hence, the result for sources observed as a function of flux, including magnification bias and radial-displacement effects. We give the corresponding linear result for a magnitude-limited survey at low redshift, and discuss the angular power spectrum of the total count distribution. We also calculate the cross correlation with the CMB polarization and temperature including Doppler source terms, magnification, redshift distortions, and other velocity effects for the sources, and discuss why the contribution of redshift distortions is generally small. Finally, we relate the result for source number counts to that for the brightness of line radiation, for example, 21 cm radiation, from the sources.

In [A. Maleknejad and M. M. Sheikh-Jabbari, arXiv:1102.1513.] we introduced an inflationary scenario, non-Abelian gauge field inflation or gauge-flation for short, in which slow-roll inflation is driven by non-Abelian gauge field minimally coupled to gravity. We present a more detailed analysis, both numerical and analytical, of the gauge-flation. By studying the phase diagrams of the theory, we show that getting enough number of e-folds during a slow-roll inflation is fairly robust to the choice of initial gauge field values. In addition, we present a detailed analysis of the cosmic perturbation theory in gauge-flation which has many special and interesting features compared the standard scalar-driven inflationary models. The specific gauge-flation model we study in this paper has two parameters, a cutoff scale $\Lambda$ and the gauge coupling $g$. Fitting our results with the current cosmological data fixes $\Lambda \sim 10H\sim {10}^{15}\mathrm{GeV}$ ($H$ is the Hubble parameter) and $g\sim {10}^{-4}$, which are in the natural range of parameters in generic particle physics beyond standard models. Our model also predicts a tensor-to-scalar ratio $r>0.05$, in the range detectable by the Planck satellite.

When quantum back-reaction by fluctuations, correlations and higher moments of a state becomes strong, semiclassical quantum mechanics resembles a dynamical system with a high-dimensional phase space. Here, systematic computational methods to derive the dynamical equations including all quantum corrections to high order in the moments are introduced, together with a (deparameterized) quantum cosmological example to illustrate some implications. The results show, for instance, that the Gaussian form of an initial state is maintained only briefly, but that the evolving state settles down to a new characteristic shape afterwards. Remarkably, even in the regime of large high-order moments, we observe a strong convergence within all considered orders that supports the use of this effective approach.

The open inflation scenario is attracting a renewed interest in the context of the string landscape. Since there are a large number of metastable de Sitter vacua in the string landscape, tunneling transitions to lower metastable vacua through the bubble nucleation occur quite naturally, which leads to a natural realization of open inflation. Although the deviation of ${\Omega }_0$ from unity is small by the observational bound, we argue that the effect of this small deviation on the large-angle CMB anisotropies can be significant for tensor-type perturbation in the open inflation scenario. We consider the situation in which there is a large hierarchy between the energy scale of the quantum tunneling and that of the slow-roll inflation in the nucleated bubble. If the potential just after tunneling is steep enough, a rapid-roll phase appears before the slow-roll inflation. In this case the power spectrum is basically determined by the Hubble rate during the slow-roll inflation. On the other hand, if such a rapid-roll phase is absent, the power spectrum keeps the memory of the high energy density there in the large angular components. Furthermore, the amplitude of large angular components can be enhanced due to the effects of the wall fluctuation mode if the bubble wall tension is small. Therefore, although even the dominant quadrupole component is suppressed by the factor $(1-{\Omega }_0{)}^2$, one can construct some models in which the deviation of ${\Omega }_0$ from unity is large enough to produce measurable effects. We also consider a more general class of models, where the false vacuum decay may occur due to Hawking-Moss tunneling, as well as the models involving more than one scalar field. We discuss scalar perturbations in these models and point out that a large set of such models is already ruled out by observational data, unless there was a very long stage of slow-roll inflation after the tunneling. These results show that observational data allow us to test various assumptions concerning the structure of the string theory potentials and the duration of the last stage of inflation.

We present evidence that a special class of gravitationally coupled hidden sectors, in which conformal invariance is dynamically broken in a controlled way, exhibit the properties of dark energy. Such quantum field theories may appear while embedding the standard model in a more fundamental high energy theory. At late times, an effective dark energy field behaves similarly to an exponentially small cosmological constant while at early times its energy density partly tracks that of matter.

One of the open questions of modern cosmology is the nature and properties of the dark matter halo and its substructures. In this work we study the gravitational effect of dark matter substructures on pulsar timing observations. Since millisecond pulsars are stable and accurate emitters, they have been proposed as plausible astrophysical tools to probe the gravitational effects of dark matter structures. We study this effect on pulsar timing through Shapiro time delay (or integrated Sachs-Wolfe (ISW) effect) and Doppler effects statistically, showing that the latter dominates the signal. For this task, we relate the power spectrum of pulsar frequency change to the matter power spectrum on small scales, which we compute using the stable clustering hypothesis, as well as other models of nonlinear structure formation. We compare this power spectrum with the reach of current and future observations of pulsar timing designed for gravitational wave detection. Our results show that while current observations are unable to detect these signals, the sensitivity of the upcoming square kilometer array is only a factor of few weaker than our optimistic predictions.

The existence of doubly charged Higgs bosons ($H^{\pm \pm }$) is a distinctive feature of the Higgs triplet model (HTM), in which neutrinos obtain tree-level masses from the vacuum expectation value of a neutral scalar in a triplet representation of $SU(2{)}_L$. We point out that a large branching ratio for the decay of a singly charged Higgs boson to a doubly charged Higgs boson via $H^{\pm }\to H^{\pm \pm }{W}^{*}$ is possible in a sizeable parameter space of the HTM. From the production mechanism $q^{\prime }\overline{q}\to W^{*}\to H^{\pm \pm }{H}^{\mp }$ the above decay mode would give rise to pair production of $H^{\pm \pm }$, with a cross section which can be comparable to that of the standard pair-production mechanism $q\overline{q}\to Z^{*}({\gamma }^{*})\to H^{++}{H}^{--}$. We suggest that the presence of a sizeable branching ratio for $H^{\pm }\to H^{\pm \pm }{W}^{*}$ could significantly enhance the detection prospects of $H^{\pm \pm }$ in the four-lepton channel. Moreover, the decays $H^0\to H^{\pm }{W}^{*}$ and $A^0\to H^{\pm }{W}^{*}$ from production of the neutral triplet scalars $H^0$ and $A^0$ would also provide an additional source of $H^{\pm }$, which can subsequently decay to $H^{\pm \pm }$.

A phenomenological analysis is presented of recent two-particle angular correlation data on relative pseudorapidity ($\eta$) and azimuth reported by the Compact Muon Solenoid (CMS) Collaboration for $\sqrt{s}=7\mathrm{TeV}$ proton-proton collisions. The data are described with an empirical jetlike model developed for similar angular correlation measurements obtained from heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC). The sameside (small relative azimuth), $\eta$-extended correlation structure, referred to as the ridge, is compared with three phenomenological correlation structures suggested by theoretical analysis. These include additional angular correlations due to soft gluon radiation in $2\to 3$ partonic processes, a one-dimensional sameside correlation ridge on azimuth motivated, for example, by color-glass condensate models, and an azimuth quadrupole similar to that required to describe heavy-ion angular correlations. The quadrupole model provides the best overall description of the CMS data, including the ridge, based on ${\chi }^2$ minimization in agreement with previous studies. Implications of these results with respect to possible mechanisms for producing the CMS sameside correlation ridge are discussed.

We investigate the scaling properties in inclusive hadron production and the associated single transverse spin asymmetry in the forward rapidity region at RHIC. We find that the spin-averaged experimental data in both $pp$ and $dAu$ collisions demonstrates a transverse-momentum-dependent geometric scaling. We introduce the transverse-momentum-dependent Collins fragmentation function to study the scaling of the single transverse spin asymmetries. The general feature of the scaling analysis is consistent with the experimental observations, in particular, for the transverse momentum dependence of the spin asymmetries at RHIC energy. We further propose to probe the saturation scale of nuclei by measuring the spin asymmetry normalized by that in $pp$ scattering at low transverse momentum.

We set up a framework for the study of the power-suppressed three-parton contribution to the pion electromagnetic form factor in the $k_T$ factorization theorem. It is first shown that the gauge dependence proportional to parton transverse momenta from the two-parton Fock state and the gauge dependence associated with the three-parton Fock state cancel each other. After verifying the gauge invariance, we derive the three-parton-to-three-parton $k_T$-dependent hard kernel at leading order of the coupling constant, and find that it leads to about 5% correction to the pion electromagnetic form factor in the whole range of experimentally accessible momentum transfer squared. This subleading contribution is much smaller than the leading-order twist-2, next-to-leading-order twist-2, and leading-order two-parton twist-3 ones, which have been calculated in the literature.