Superspinars are ultracompact objects whose mass $M$ and angular momentum $J$ violate the Kerr bound ($cJ/G{M}^2>1$). Recent studies analyzed the observable consequences of gravitational lensing and accretion around superspinars in astrophysical scenarios. In this paper we investigate the dynamical stability of superspinars to gravitational perturbations, considering either purely reflecting or perfectly absorbing boundary conditions at the “surface” of the superspinar. We find that these objects are unstable independently of the boundary conditions, and that the instability is strongest for relatively small values of the spin. Also, we give a physical interpretation of the various instabilities that we find. Our results (together with the well-known fact that accretion tends to spin superspinars down) imply that superspinars are very unlikely astrophysical alternatives to black holes.

Recent anomalies in cosmic rays data, namely, from the PAMELA Collaboration, can be interpreted in terms of TeV scale decaying/annihilating dark matter. We analyze the impact of radiative corrections coming from the electroweak sector of the standard model on the spectrum of the final products at the interaction point. As an example, we consider virtual one loop corrections and real gauge bosons emission in the case of a very heavy vector boson annihilating into fermions. We find electroweak corrections that are relevant, but not as big as sometimes found in the literature; we relate this mismatch to the issue of gauge invariance. At scales much higher than the symmetry breaking scale, one loop electroweak effects are so big that eventually higher orders/resummations have to be considered: we advocate for the inclusion of these effects in parton shower Monte Carlo models aiming at the description of TeV scale physics.

We consider a model where electroweak symmetry breaking is driven by technicolor dynamics with minimal particle content required for walking coupling and saturation of global anomalies. Furthermore, the model features three additional Weyl fermions singlet under technicolor interactions, two of which provide for a one-loop unification of the standard model gauge couplings. Among these extra matter fields exists a possible candidate for weakly interacting dark matter. We evaluate the relic densities and find that they are sufficient to explain the cosmological observations and avoid the experimental limits from earth-based searches. Hence, we establish a nonsupersymmetric framework where hierarchy and naturality problems are solved, coupling constant unification is achieved, and a plausible dark matter candidate exists.

This paper makes two points. First, we show that the line-of-sight solution to cosmic microwave anisotropies in Fourier space, even though formally defined for arbitrarily large wavelengths, leads to position-space solutions which only depend on the sources of anisotropies inside the past light cone of the observer. This foretold manifestation of causality in position (real) space happens order by order in a series expansion in powers of the visibility $\gamma =e^{-\mu }$, where $\mu$ is the optical depth to Thomson scattering. We show that the contributions of order ${\gamma }^N$ to the cosmic microwave background (CMB) anisotropies are regulated by spacetime window functions which have support only inside the past light cone of the point of observation. Second, we show that the Fourier-Bessel expansion of the physical fields (including the temperature and polarization momenta) is an alternative to the usual Fourier basis as a framework to compute the anisotropies. The viability of the Fourier-Bessel series for treating the CMB is a consequence of the fact that the visibility function becomes exponentially small at redshifts $z\gg {10}^3$, effectively cutting off the past light cone and introducing a finite radius inside which initial conditions can affect physical observables measured at our position $\overrightarrow{x}=0$ and time $t_0$. Hence, for each multipole $\ell$ there is a discrete tower of momenta $k_{i\ell }$ (not a continuum) which can affect physical observables, with the smallest momenta being $k_{1\ell }\sim \ell$. The Fourier-Bessel modes take into account precisely the information from the sources of anisotropies that propagates from the initial value surface to the point of observation—no more, no less. We also show that the physical observables (the temperature and polarization maps), and hence the angular power spectra, are unaffected by that choice of basis. This implies that the Fourier-Bessel expansion is the optimal scheme with which one can compute CMB anisotropies.

Slow-roll inflation is studied in theories where the inflaton field is conformally coupled to the Ricci scalar. In particular, the case of Higgs field inflation in the context of the noncommutative spectral action is analyzed. It is shown that while the Higgs potential can lead to the slow-roll conditions being satisfied once the running of the self-coupling at two-loops is included, the constraints imposed from the CMB data make the predictions of such a scenario incompatible with the measured value of the top quark mass. We also analyze the role of an additional conformally coupled massless scalar field, which arises naturally in the context of noncommutative geometry, for inflationary scenarios.

The loop quantum cosmology “improved dynamics” of the Bianchi type IX model are studied. The action of the Hamiltonian constraint operator is obtained via techniques developed for the Bianchi type I and type II models, no new input is required. It is shown that the big bang and big crunch singularities are resolved by quantum gravity effects. We also present effective equations which provide quantum geometry corrections to the classical equations of motion.

The new release of data from Wilkinson Microwave Anisotropy Probe improves the observational status of relic gravitational waves. The 7-year results enhance the indications of relic gravitational waves in the existing data and change to the better the prospects of confident detection of relic gravitational waves by the currently operating Planck satellite. We apply to WMAP7 data the same methods of analysis that we used earlier [W. Zhao, D. Baskaran, and L. P. Grishchuk, Phys. Rev. D 80, 083005 (2009)] with WMAP5 data. We also revised by the same methods our previous analysis of WMAP3 data. It follows from the examination of consecutive WMAP data releases that the maximum likelihood value of the quadrupole ratio $R$, which characterizes the amount of relic gravitational waves, increases up to $R=0.264$, and the interval separating this value from the point $R=0$ (the hypothesis of no gravitational waves) increases up to a $2\sigma$ level. The primordial spectra of density perturbations and gravitational waves remain blue in the relevant interval of wavelengths, but the spectral indices increase up to $n_s=1.111$ and $n_t=0.111$. Assuming that the maximum likelihood estimates of the perturbation parameters that we found from WMAP7 data are the true values of the parameters, we find that the signal-to-noise ratio $S/N$ for the detection of relic gravitational waves by the Planck experiment increases up to $S/N=4.04$, even under pessimistic assumptions with regard to residual foreground contamination and instrumental noises. We comment on theoretical frameworks that, in the case of success, will be accepted or decisively rejected by the Planck observations.

Scale invariance may be a classical symmetry which is broken radiatively. This provides a simple way to stabilize the scale of electroweak symmetry breaking against radiative corrections. But for such a theory to be fully realistic, it must actually incorporate a hierarchy of scales, including the Planck and the neutrino mass scales in addition to the electroweak scale. The dark matter sector and the physics responsible for baryogenesis may or may not require new scales, depending on the scenario. We develop a generic way of using hidden sectors to construct a technically-natural hierarchy of scales in the framework of classically scale-invariant theories. We then apply the method to generate the Planck mass and to solve the neutrino mass and dark matter problems through what may be termed the “scale-invariant standard model.” The model is perturbatively renormalizable for energy scales up to the Planck mass.

Late-decaying string moduli dilute the baryon asymmetry of the Universe created in any previous era. The reheat temperature for such moduli is below a GeV, thus motivating baryogenesis at very low temperatures. We present an extension of the minimal supersymmetric standard model with TeV-scale colored fields that can yield the correct baryon asymmetry of the Universe in this context. Modulus decay, which reheats the Universe at a temperature below GeV, produces the visible sector fields and neutralino dark matter in nonthermal fashion. We discuss various possibilities for baryogenesis from TeV-scale colored fields and show that they can generate an acceptable baryon asymmetry, while being compatible with phenomenological constraints like neutron-antineutron oscillation.

We analyze the chiral phase transition with the help of the QCD gap equation. Various models for the effective interaction in rainbow truncation are contrasted with regard to the resulting chiral transition temperatures. In particular, we investigate possible systematic relations of the details of the effective interaction and the value of $T_c$. In addition, we quantify changes to the transition temperature beyond the rainbow truncation.

Beauty and charm $e^{+}{e}^{-}$ factories running at resonance thresholds have unique capabilities for studies of the production of light dark matter particles in the decays of $B_q(D)$ meson pairs. We provide a comprehensive study of light dark matter production in heavy meson decays with missing energy $\mathrm{E̸}$ in the final state, such as $B_q(D^0)\to \mathrm{E̸}$ and $B_q(D^0)\to \gamma \mathrm{E̸}$. We argue that such transitions can be studied at the current flavor factories (and future superflavor factories) by tagging the missing-energy decays with $B(D^0)$ decays “on the other side.”

We continue the development of a nonperturbative light-front Hamiltonian method for the solution of quantum field theories by considering the one-photon eigenstate of Lorentz-gauge QED. The photon state is computed nonperturbatively for a Fock basis with a bare photon state and electron-positron pair states. The calculation is regulated by the inclusion of Pauli-Villars (PV) fermions, with one flavor to make the integrals finite and a second flavor to guarantee a zero mass for the physical photon eigenstate. We compute in detail the constraints on the PV coupling strengths that this zero mass implies. As part of this analysis, we provide the complete Lorentz-gauge light-front QED Hamiltonian with two PV fermion flavors and two PV photon flavors, which will be useful for future work. The need for two PV photons was established previously; the need for two PV fermions is established here.

We propose a $E_6$ inspired supersymmetric model with a non-Abelian discrete flavor symmetry ($S_4$ group); that is, $SU(3{)}_c\times SU(2{)}_W\times U(1{)}_Y\times U(1{)}_X\times S_4\times Z_2$. In our scenario, the additional Abelian gauge symmetry, $U(1{)}_X$, not only solves the $\mu$ problem in the minimal supersymmetric standard model but also requires new exotic fields which play an important role in solving flavor puzzles. If our exotic quarks can be embedded into a $S_4$ triplet, which corresponds to the number of the generation, one finds that dangerous proton decay can be well suppressed. Hence, it might be expected that the generation structure for lepton and quark in the standard model can be understood as a new system in order to stabilize the proton in a supersymmetric standard model. Moreover, because of the nature of the discrete non-Abelian symmetry itself, Yukawa coupling constants of our model are drastically reduced. In our paper, we show two predictive examples of the models for quark sector and lepton sector, respectively.

In the AdS/CFT duality, it is often said that a local symmetry in a bulk theory corresponds to a global symmetry in the corresponding boundary theory, but the global symmetry can become local when one couples with an external source. As a result, the Gubser-Klebanov-Polyakov-Witten relation gives a response function instead of a Green function. We explore this point in detail using the example of holographic superconductors. We point out that these points play a crucial role in interpreting the holographic London equation properly.

We consider a dual description of the technicolor-like gauge theory within the $\mathrm{D}4/\mathrm{D}8$-brane configuration with varying confinement and electroweak symmetry breaking scales. Constructing an effective truncated model valid below a certain cutoff, we identify the particle spectrum with Kaluza-Klein modes of the model in a manner consistent with the hidden local symmetry. Integrating out heavy states, we find that the low-energy action receives nontrivial corrections stemming from the mixing between standard model and heavy gauge bosons, which results in reduction of oblique parameters.

We derive a special scalar field potential using the anisotropic Bianchi type I cosmological model from canonical quantum cosmology under determined conditions in the evolution to anisotropic variables ${\beta }_{\pm }$. In the process, we obtain a family of potentials that has been introduced by hand in the literature to explain cosmological data. Considering supersymmetric quantum cosmology, this family is scanned, fixing the exponential potential as more viable in the inflation scenario $V(\varphi )=V_0{e}^{-\sqrt{3}\varphi }$.

We introduce a new regularization for Thiemann’s Hamiltonian constraint. The resulting constraint can generate the 1–4 Pachner moves and is therefore more compatible with the dynamics defined by the spinfoam formalism. We calculate its matrix elements and observe the appearance of the $15j$ Wigner symbol in these.

The chameleonic behavior of the string theory dilaton is suggested. Some of the possible consequences of the chameleonic string dilaton are analyzed in detail. In particular, (1) we suggest a new stringy solution to the cosmological constant problem and (2) we point out the nonequivalence of different conformal frames at the quantum level. In order to obtain these results, we start taking into account the (strong coupling) string loop expansion in the string frame (S-frame), therefore the so-called form factors are present in the effective action. The correct dark energy scale is recovered in the Einstein frame (E-frame) without unnatural fine-tunings and this result is robust against all quantum corrections, granted that we assume a proper structure of the S-frame form factors in the strong coupling regime. At this stage, the possibility still exists that a certain amount of fine-tuning may be required to satisfy some phenomenological constraints. Moreover in the E-frame, in our proposal, all the interactions are switched off on cosmological length scales (i.e., the theory is IR-free), while higher derivative gravitational terms might be present locally (on short distances) and it remains to be seen whether these facts clash with phenomenology. A detailed phenomenological analysis is definitely necessary to clarify these points.

The ‘‘effective geometry” formalism is used to study the perturbations of a perfect barotropic Newtonian self-gravitating rotating and compressible fluid coupled with gravitational backreaction. The case of a uniformly rotating polytrope with index $n=1$ is investigated, due to its analytical tractability. Special attention is devoted to the geometrical properties of the underlying background acoustic metric, focusing, in particular, on null geodesics as well as on the analog light cone structure.

This note is devoted to the study of Hamiltonian formulation of modified $F(R)$ Hořava-Lifshitz theories of gravity that were proposed recently by Chaichian and collaborators [arXiv:1001.4102]. We also study Hamiltonian formulation of the healthy extended Hořava-Lifshitz gravities and show that these theories have the Hamiltonian structure that is different from Hamiltonian formulation general relativity.