We consider cosmological models with a non–scale-invariant spectrum of primordial perturbations and assess whether they represent a viable alternative to the concordance $\Lambda \mathrm{CDM}$ model. We find that in the framework of a model selection analysis, the WMAP and 2dF data do not provide any conclusive evidence in favor of one or the other kind of model. However, when a marginalization over the entire space of nuisance parameters is performed, models with a modified primordial spectrum and ${\Omega }_{\Lambda }=0$ are strongly disfavored.

The large-scale structure of the Universe, as traced by the distribution of galaxies, is now being revealed by large-volume cosmological surveys. The structure is characterized by galaxies distributed along filaments, the filaments connecting in turn to form a percolating network. Our objective here is to quantitatively specify the underlying mechanisms that drive the formation of the cosmic network: By combining percolation-based analyses with $N$-body simulations of gravitational structure formation, we elucidate how the network has its origin in the properties of the initial density field (nature) and how its contrast is then amplified by the nonlinear mapping induced by the gravitational instability (nurture).

Predictions of the thermodynamic conditions for phase transitions at high baryon densities and large chemical potentials are currently uncertain and largely phenomenological. Neutrino observations of core-collapse supernovae can be used to constrain the situation. Recent simulations of stellar core collapse that include a description of quark matter predict a sharp burst of ${\overline{\nu }}_e$ several hundred milliseconds after the prompt ${\nu }_e$ neutronization burst. We study the observational signatures of that ${\overline{\nu }}_e$ burst at current neutrino detectors—IceCube and Super-Kamiokande. For a Galactic core-collapse supernova, we find that signatures of the QCD phase transition can be detected, regardless of the neutrino oscillation scenario. The detection would constitute strong evidence of a phase transition in the stellar core, with implications for the equation of state at high matter density and the supernova explosion mechanism.

We show that a massive black hole binary might resonantly trap a small third body (e.g. a neutron star) down to a stage when the binary becomes relativistic due to its orbital decay by gravitational radiation. The final fate of the third body would be quite interesting for relativistic astrophysics. For example, the parent binary could expel the third body with a velocity more than 10% of the speed of light. We also discuss the implications of this three-body system for direct gravitational wave observation.

We compute the masses of the singly and doubly charmed baryons in full QCD using the relativistic Fermilab action for the charm quark. For the light quarks we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. We use the low-lying charmonium spectrum to tune our heavy-quark action and as a guide to understanding the discretization errors associated with the heavy quark. Our results are in good agreement with experiment within our systematics. For the ${\Xi }_{cc}$, we find the isospin-averaged mass to be $M_{{\Xi }_{cc}}=3665\pm 17\pm {14}_{-78}^{+0}\mathrm{MeV}$; the three given uncertainties are statistical, systematic, and an estimate of lattice discretization errors, respectively. In addition, we predict the mass splitting of the (isospin-averaged) spin-$1/2$ ${\Omega }_{cc}$ with the ${\Xi }_{cc}$ to be $M_{{\Omega }_{cc}}-M_{{\Xi }_{cc}}=98\pm 9\pm 22\pm 13\mathrm{MeV}$ (in this mass splitting, the leading discretization errors are also suppressed by $SU(3)$ symmetry). Combining this splitting with our determination of $M_{{\Xi }_{cc}}$ leads to our prediction of the spin-$1/2$ ${\Omega }_{cc}$ mass, $M_{{\Omega }_{cc}}=3763\pm 19\pm {26}_{-79}^{+13}\mathrm{MeV}$.

A search for $J/\psi$ radiative decay to weakly interacting neutral final states was performed using the CLEO-c detector at the Cornell Electron Storage Ring. $J/\psi$ events were selected by observing the hadronic decay $\psi (2S)\to {\pi }^{+}{\pi }^{-}J/\psi$. A total of $3.7\times {10}^6$ $J/\psi$ events were used to study the decay $J/\psi \to \gamma +X$, where $X$ is a narrow state that is invisible to the detector. No significant signal was observed, and upper limits on the branching fraction were set for masses $m_X$ up to $960\mathrm{MeV}/c^2$. The upper limit corresponding to $m_X=0$ is $4.3\times {10}^{-6}$ at the 90% confidence level.

In this article the anomalous dimension of a class of operators with a bare dimension of $O(N)$ is studied. The operators considered are dual to excited states of a two giant graviton system. In the Yang-Mills theory they are described by restricted Schur polynomials, labeled with Young diagrams that have at most two columns. In a certain limit the dilatation operator looks like a lattice version of a second derivative, with the lattice emerging from the Young diagram itself.

The appearance of a few unevenly spaced bright flashes of light on top of Hawking radiation is the sign of the amplification effect in black hole horizon fluctuations. Previous studies on this problem suffer from the lack of considering all emitted photons in the theoretical spectroscopy of these fluctuations. In this paper, we include all of the physical transition weights and present a consistent intensity formula. This modifies a black hole radiation pattern.

In this paper, we calculate in a transparent way the spectral dimension of a quantum spacetime, considering a diffusion process propagating on a fluctuating manifold. To describe the erratic path of the diffusion, we implement a minimal length by averaging the graininess of the quantum manifold in the flat space case. As a result we obtain that, for large diffusion times, the quantum spacetime behaves like a smooth differential manifold of discrete dimension. On the other hand, for smaller diffusion times, the spacetime looks like a fractal surface with a reduced effective dimension. For the specific case in which the diffusion time has the size of the minimal length, the spacetime turns out to have a spectral dimension equal to 2, suggesting a possible renormalizable character of gravity in this regime. For smaller diffusion times, the spectral dimension approaches zero, making any physical interpretation less reliable in this extreme regime. We extend our result to the presence of a background field and curvature. We show that in this case the spectral dimension has a more complicated relation with the diffusion time, and conclusions about the renormalizable character of gravity become less straightforward with respect to what we found with the flat space analysis.

Our Universe is ruled by quantum mechanics and its extension quantum field theory. However, the explanations for a number of cosmological phenomena such as inflation, dark energy, symmetry breakings, and phase transitions need the presence of classical scalar fields. Although the process of condensation of scalar fields in the lab is fairly well understood, the extension of results to a cosmological context is not trivial. Here we investigate the formation of a condensate—a classical scalar field—after reheating of the Universe. We assume a light quantum scalar field produced by the decay of a heavy particle, which for simplicity is assumed to be another scalar. We show that during the radiation domination epoch under certain conditions, the decay of the heavy particle alone is sufficient for the production of a condensate. This process is very similar to preheating—the exponential particle production at the end of inflation. During the matter domination epoch when the expansion of the Universe is faster, the decay alone cannot keep the growing trend of the field and the amplitude of the condensate decreases rapidly, unless there is a self-interaction. This issue is particularly important for dark energy. We show that quantum corrections of the self-interaction play a crucial role in this process. Notably, they induce an effective action which includes inverse power-law terms, and therefore can lead to a tracking behavior even when the classical self-interaction is a simple power-law of order 3 or 4. This removes the necessity of having nonrenormalizable terms in the Lagrangian. If dark energy is the condensate of a quantum scalar field, these results show that its presence is deeply related to the action of quantum physics at the largest observable scales.

A recently proposed $SO(5)\times U(1)$ gauge-Higgs unification model in the Randall-Sundrum warped space contains a very interesting dark matter candidate, the Higgs boson. As a part of the fifth component of a five-dimensional gauge field, the four-dimensional neutral Higgs boson has odd $H$ parity while all the other standard model particles have even parity to all orders in perturbation theory. Based on $H$ parity conserving $WWHH$ and $ZZHH$ vertices, we investigate the collider signatures of Higgs dark matter production associated with a standard model $W$ or $Z$ gauge boson at the LHC and the International Linear Collider (ILC). The final state consists of a $W$ or a $Z$ boson with large missing energy. We found that the level of the signal cross section is quite hopeless at the LHC, while we may be able to identify it at the ILC with polarized electron beams.

We investigate deep inelastic scattering off the polarized “neutron” using gauge/string duality. The “neutron” corresponds to a supergravity mode of the neutral dilatino. Through introducing the Pauli interaction term into the action in ${\mathrm{AdS}}_5$ space, we calculate the polarized deep inelastic structure functions of the “neutron” in supergravity approximation at large t’ Hooft coupling $\lambda$ and finite $x$ with ${\lambda }^{-1/2}\ll x<1$. In comparison with the charged dilatino-“proton,” which has been obtained in the previous work by Gao and Xiao, we find the structure functions of the “neutron” are power suppressed at the same order as the ones of the “proton.” Especially, we find the Burkhardt-Cottingham-like sum rule, which is satisfied in the work by Gao and Xiao, is broken due to the Pauli interaction term. We also illustrate how such a Pauli interaction term can arise naturally from higher dimensional fermion-graviton coupling through the usual Kaluza-Klein reduction.

We study the quark mass function on hypercubic lattices in a large range of physical volumes and cutoffs. To avoid the very large Wilson term artefact, we exploit the relation between the quark mass function and the pseudoscalar vertex in the continuum. We extrapolate to the chiral limit. In function of the physical volume, we observe a striking discontinuity in the properties of chiral extrapolation around a physical volume $L_c\simeq 6{\mathrm{GeV}}^{-1}=1.2\mathrm{fm}$. It is present in the quark mass function, which collapses to zero, as well as in the pion mass and the quark condensate as directly calculated from the pseudoscalar correlator. It is strongly reminiscent of the phenomenon of chiral symmetry restoration observed by Neuberger and Narayanan at $N_C=\infty$ around the same physical length. In the case of spontaneous symmetry breaking, we confirm that the operator product expansion of the quark mass function, involving the quark condensate, is not operative at the available momenta, even taking into account the unusually large high order corrections to the Wilson coefficient calculated by Chetyrkin and Maier; the gap remains large, around a factor 2, even at the largest momenta available to us ($p\simeq 6\mathrm{GeV}$).

New high-statistics Belle data on the reaction $\gamma \gamma \to {\pi }^0\eta$ are analyzed to clarify the two-photon production mechanisms and the nature of the $a_0(980)$ meson. The obtained solution for the amplitude $\gamma \gamma \to {\pi }^0\eta$ is consistent with the chiral theory expectation for the $\pi \eta$ scattering length, with the strong coupling of the $a_0(980)$ to the $\pi \eta$, $K\overline{K}$, and $\pi {\eta }^{\prime }$ channels, and with a key role of the rescattering mechanisms $a_0(980)\to (K\overline{K}+{\pi }^0\eta +{\pi }^0{\eta }^{\prime })\to \gamma \gamma$ in the $a_0(980)\to \gamma \gamma$ decay. Such a picture argues in favor of the $q^2{\overline{q}}^2$ nature of the $a_0(980)$ meson and is in agreement with the properties of its partners, the ${\sigma }_0(600)$ and $f_0(980)$ mesons, in particular, with those that manifest themselves in $\gamma \gamma \to \pi \pi$. An important role of the vector meson exchanges in the formation of the nonresonant background in $\gamma \gamma \to {\pi }^0\eta$ is also revealed. The preliminary information on the reaction ${\pi }^0\eta \to {\pi }^0\eta$ is obtained.

We discuss on very general grounds possible lineshapes of composite particles with one unstable constituent. Expressions are derived in a coupled-channel formalism for constituents interacting in an $S$-wave with no assumption made on the width of one of them. We show how easy-to-use formulas, already existing in the literature, emerge for narrow constituents and identify the parameter that controls the regime of their applicability.

We present a detailed study of the effect of internal bremsstrahlung photons in the context of the minimal supersymmetric standard models and their impact on $\gamma$-ray dark matter annihilation searches. We find that, although this effect has to be included for the correct evaluation of fluxes of high energy photons from neutralino annihilation, its contribution is relevant only in models and at energies where the lines contribution is dominant over the secondary photons. Therefore, we find that the most optimistic supersymmetric scenarios for dark matter detection do not change significantly when including the internal bremsstrahlung. As an example, we review the $\gamma$-ray dark matter detection prospects of the Draco dwarf spheroidal galaxy for the MAGIC stereoscopic system and the CTA project. Though the flux of high energy photons is enhanced by an order of magnitude in some regions of the parameter space, the expected fluxes are still much below the sensitivity of the instruments.

We continue the analysis of the $D$-deformed Wess-Zumino model that we introduced in M. Dmitrijevic and V. Radovanovic, J. High Energy Phys. 04 (2009) 108. The model is defined by a deformation that is non-Hermitian and given in terms of the covariant derivatives $D_{\alpha }$. We calculate one-loop divergences in the two-point, three-point, and four-point Green functions. Possibilities to render the model renormalizable are discussed.

We consider spatially homogeneous and isotropic Friedmann-Robertson-Walker solutions of Milgrom’s recently proposed class of bimetric theories of gravity. These theories have two different regimes, corresponding to high and low acceleration. We find simple power-law matter dominated solutions in both, as well as solutions with spatial curvature, and exponentially expanding solutions. In the high acceleration limit these solutions behave like the Friedmann-Robertson-Walker solutions of general relativity, with a cosmological constant term that is of the correct order of magnitude to explain the observed accelerating expansion of the Universe. We find that solutions that remain in the high acceleration regime for their entire history, however, require nonbaryonic dark matter fields, or extra interaction terms in their gravitational Lagrangian, in order to be observationally viable. The low acceleration regime also provides some scope to account for this deficit, with solutions that differ considerably from their general relativistic counterparts.

In this paper we study various particle physics effects of a light, scalar dark energy field with chameleonlike couplings to matter. We show that a chameleon model with only matter couplings will induce a coupling to photons. In doing so, we derive the first microphysical realization of a chameleonic dark energy model coupled to the electromagnetic field strength. This analysis provides additional motivation for current and near-future tests of axionlike and chameleon particles. We find a new bound on the coupling strength of chameleons in uniformly coupled models. We also study the effect of chameleon fields on Higgs production, which is relevant for hadron colliders. These are expected to manufacture Higgs particles through weak boson fusion, or associated production with a $Z$ or $W^{\pm }$. We show that, like the Tevatron, the LHC will not be able to rule out or observe chameleons through this mechanism, because gauge invariance of the low energy Lagrangian suppresses the corrections that may arise.

We evaluate the charged current neutrino-nucleon total cross section up to neutrino energies of ${10}^{12}\mathrm{GeV}$ in the leading order and next-to-leading order of perturbative QCD within the framework of two different factorization schemes. The numerical implications of some inconsistent QCD calculations are illustrated.