We perform the complete stability study of the model of chromo-natural inflation by Adshead and Wyman [Phys. Rev. Lett. 108, 261302 (2012)], where, due to its coupling to a SU(2) vector, a pseudoscalar inflaton $\chi$ slowly rolls on a steep potential. As a typical example, one can consider an axion with a sub-Planckian decay constant $f$. The model was recently studied by Dimastrogiovanni, Fasiello, and Tolley [J. Cosmol. Astropart. Phys. 02, 046 (2013)] in the $m_g\gg H$ limit, where $m_g$ is the mass of the fluctuations of the vector field, and $H$ the Hubble rate. We show that the inflationary solution is stable for $m_g>2H$, while it otherwise experiences a strong instability due to scalar perturbations in the subhorizon regime. The tensor perturbations are instead enhanced at large $m_g$, while the vector ones remain perturbatively small. Depending on the parameters, this model can give a chiral gravity wave signal that can be detected in ongoing or forthcoming cosmic microwave background experiments. This detection can occur even if, during inflation, the inflaton spans an interval of size $\Delta \chi =\mathrm{O}(f)$ which is some orders of magnitude below the Planck scale, evading a well known bound that holds for a free inflaton by Lyth [Phys. Rev. Lett. 78, 1861 (1997)]. The spectral tilt of the scalar perturbations typically decreases with decreasing $m_g$. Therefore the simultaneous requirements of stability, sufficiently small tensor-to-scalar ratio, and sufficiently flat scalar spectrum can pose nontrivial bounds on the parameters of the model.

We use a phase space approach to study possible consequences of fixed points in a single fluid flat Friedmann-Lemaître-Robertson-Walker (FLRW) models with pressure $p(H)$, where $H$ is the Hubble parameter. One of these consequences is that a fluid with a differentiable pressure, i.e., a finite adiabatic speed of sound, reaches a fixed point in an infinite time and has no finite-time singularities of types I, II, and III described by Nojiri, Odintsov, and Tsujikawa [Phys. Rev. D 71, 063004 (2005)]. It is impossible for such a fluid to cross the phantom divide in a finite time. We show that a divergent $dp/dH$, or the speed of sound, is a necessary but not sufficient condition for phantom crossing. We use pressure properties, such as asymptotic behavior and fixed points, to qualitatively describe the entire behavior of a solution in flat FLRW models. We discuss FLRW models with bulk viscosity $\eta \sim {\rho }^r$, in particular, solutions for $r=1$ and $r=1/4$ cases, which can be expressed in terms of the Lambert-$W$ function. The last solution behaves as either a nonsingular phantom fluid or a unified dark fluid. Using causality and stability constraints, we show that the universe must end as a de Sitter space. Relaxing the stability constraint leads to a de Sitter universe, an empty universe, or a turnaround solution that reaches a maximum size and then recollapses.

We show that consistent nonlinear partially massless models cannot be obtained starting from “$f\mathrm{\text{−}}g$” massive gravity, with “$f$” the embedding de Sitter space. The obstruction, which is also the source of $f\mathrm{\text{−}}g$ acausality, is the very same fifth constraint that removes the notorious sixth ghost excitation. Here, however, it blocks extension of the gauge invariance (appearing for mass to de Sitter cosmological constant tunings) that removed the helicity-zero mode at linear level. Separately, our methods allow us to almost complete the proof that all $f\mathrm{\text{−}}g$ models are acausal.

We propose minimal and renormalizable nonsupersymmetric top $SU(5)$ models where the $SU(5)\times SU(3{)}_C^{\prime }\times SU(2{)}_L^{\prime }\times U(1{)}_Y^{\prime }$ gauge symmetry is broken down to the Standard Model gauge symmetry at the TeV scale. The first two families of the Standard Model fermions are charged under $SU(3{)}_C^{\prime }\times SU(2{)}_L^{\prime }\times U(1{)}_Y^{\prime }$, while the third family is charged under $SU(5)$. In the minimal top $SU(5)$ model, we show that the quark Cabibbo-Kobayashi-Maskawa mixing matrix can be generated via dimension-five operators, and the proton decay problem can be solved by fine-tuning the coefficients of the higher-dimensional operators at the order of ${10}^{-4}$. In the renormalizable top $SU(5)$ model, we can explain the quark Cabibbo-Kobayashi-Maskawa mixing matrix by introducing vectorlike particles, and we do not have the proton decay problem. The models give rise to leptoquark and diquark gauge bosons which violate both lepton and baryon numbers involving the third-family quarks and leptons. The current experimental limits for these particles is well below the TeV scale. We also discuss the productions and decays of these new gauge bosons, and their ensuing signals, as well as their reach at the LHC.

An extra dimension is one of the most attractive candidates beyond the Standard Model. In warped extra dimensional space-time, not only the gauge hierarchy problem but also quark-lepton mass hierarchy can be naturally explained. In this setup, a sizable parity violation through a Kaluza-Klein gluon exchange appears in the QCD process such as helicity dependent top pair production. We investigate this QCD parity violating process by use of the $SO(5)\times U(1)$ gauge-Higgs unification model. We evaluate LHC observable quantities, i.e., a charge asymmetry and a forward-backward asymmetry of the top pair production, and find that a sizable charge asymmetry can be observed with specific model parameters.

We study the ${\rm Y}$ exclusive decay into double charmonium, specifically, the $S$-wave charmonium $J/\psi$ plus the $P$-wave charmonium ${\chi }_{c0,1,2}$ in the nonrelativistic QCD factorization framework. Three distinct decay mechanisms, i.e., the strong, electromagnetic, and radiative decay channels, are included, and their interference effects are investigated. The decay processes ${\rm Y}(1S,2S,3S)\to J/\psi +{\chi }_{c1,0}$ are predicted to have the branching fractions of order ${10}^{-6}$, which should be observed in the prospective Super $B$ factory.

We propose a mechanism which provides an explanation of the Gallium and antineutrino reactor anomalies. Differently from original Pontecorvo’s hypothesis, this mechanism is based on the phenomenological assumption in which the admixture of neutrino mass eigenstates in the moments of neutrino creation and detection can assume different configurations around the admixture parametrized by the usual values of the mixing angles ${\theta }_{12}$, ${\theta }_{23}$, and ${\theta }_{13}$. For simplicity, we assume a Gaussian distribution for the mixing angles in such a way that the average value of this distribution is given by the usual values of the mixing angles, and the width of the Gaussian is denoted by $\alpha$. We show that the proposed mechanism provides a possible explanation for very short-baseline neutrino disappearance, necessary to accommodate Gallium and antineutrino reactor anomalies, which is not allowed in usual neutrino oscillations based on Pontecorvo’s original hypotheses. We also can describe high-energy oscillation experiments, like LSND, Fermi, and NuTeV, assuming a weakly energy dependent width parameter, $\alpha (E)$, that nicely fits all experimental results.

The near future mm/sub-mm very long baseline interferometry experiments are ambitious projects aiming at imaging the “shadow” of the supermassive black hole candidate at the center of the Milky Way and of the ones in nearby galaxies. An accurate observation of the shape of the shadow can potentially test the nature of these objects and verify if they are Kerr black holes, as predicted by general relativity. However, previous work on the subject has shown that the shadows produced in other spacetimes are very similar to the one of the Kerr background, suggesting that tests of strong gravity are not really possible with these facilities in the near future. In this work, I instead point out that it will be relatively easy to distinguish black holes from wormholes, topologically nontrivial structures of the spacetime that might have been formed in the early Universe and might connect our Universe with other universes.

During heavy ion collisions, high temperatures and strong magnetic fields are generated. We employ the gauge-gravity duality to study the $N_f=2$ QCD phase diagram under these extreme conditions in the quenched approximation; in particular we use the non-antipodal Sakai-Sugimoto model (SSM). We take the different coupling of up and down flavors to the magnetic field into account geometrically, resulting in a split of the chiral phase transition according to flavor. We discuss the influence of the magnetic field on the chiral temperatures—in physical GeV units—in terms of the choice of the confinement scale in the model, extending hereby our elsewhere presented discussion of fixing the non-antipodal SSM parameters to the deconfinement phase. The flavor-dependent $(T,L,eB)$ phase diagram, with variable asymptotic brane-antibrane separation $L$, is also presented, as a direct generalization of the known $(T,L)$ phase diagram of the non-antipodal SSM at zero magnetic field. In particular, for sufficiently small $L$ we are probing a Nambu-Jona-Lasinio (NJL)–like boundary field theory in which case we do find results very reminiscent of the predictions in NJL models.

In the context of the fuzzball program, we investigate deforming the microscopic string description of the D1-D5 system on $T^4\times S^1$ away from the orbifold point. Using conformal perturbation theory and a generalization of Lunin-Mathur symmetric orbifold technology for computing twist-nontwist correlators developed in a companion paper Burrington et al., arXiv:1211.6689, we initiate a program to compute the anomalous dimensions of low-lying string states in the D1-D5 superconformal field theory. Our method entails finding four-point functions involving a string operator $\mathcal{O}$ of interest and the deformation operator, taking coincidence limits to identify which other operators mix with $\mathcal{O}$, subtracting the identified conformal family to isolate other contributions to the four-point function, finding the mixing coefficients, and iterating. For the lowest-lying string modes, this procedure should truncate in a finite number of steps. We check our method by showing how the operator dual to the dilaton does not participate in mixing that would change its conformal dimension, as expected. Next we complete the first stage of the iteration procedure for a low-lying string state of the form $\partial X\partial X\overline{\partial }X\overline{\partial }X$ and find its mixing coefficient. Our most interesting qualitative result is evidence of operator mixing at first order in the deformation parameter, which means that the string state acquires an anomalous dimension. After diagonalization this will mean that anomalous dimensions of some string states in the D1-D5 superconformal field theory must decrease away from the orbifold point while others increase.

We investigate some higher-loop structural properties of the $\beta$ function in asymptotically free vectorial gauge theories. Our main focus is on theories with fermion contents that lead to an infrared (IR) zero in $\beta$. We present analytic and numerical calculations of the value of the gauge coupling where $\beta$ reaches a minimum, the value of $\beta$ at this minimum, and the slope of $\beta$ at the IR zero, at two-, three-, and four-loop order. The slope of $\beta$ at the IR zero is relevant for estimates of a dilaton mass in quasiconformal gauge theories. Some inequalities are derived concerning the dependence of the above quantities on loop order. A general inequality is derived concerning the dependence of the shift of the IR zero of $\beta$, from the $n$-loop to the ($n+1$)-loop order, on the sign of the ($n+1$)-loop coefficient in $\beta$. Some results are also given for gauge theories with $\mathcal{N}=1$ supersymmetry.

The scattering theory approach makes it possible to carry out exact calculations of Casimir energies in any geometry for which the scattering $T$-matrix and a partial wave expansion of the free Green’s function are available. We implement this program for the case of a perfectly conducting elliptic cylinder, thereby completing the set of geometries where electromagnetic scattering is separable. Particular emphasis is placed on the case of zero radius, where the elliptic cylinder reduces to a strip.

We perform full three-dimensional numerical relaxations of isospinning Hopf solitons with Hopf charge up to 8 in the Skyrme-Faddeev model with mass terms included. We explicitly allow the soliton solution to deform and to break the symmetries of the static configuration. It turns out that the model with its rich spectrum of soliton solutions, often of similar energy, allows for transmutations, formation of new solution types, and the rearrangement of the spectrum of minimal-energy solitons in a given topological sector when isospin is added. We observe that the shape of isospinning Hopf solitons can differ qualitatively from that of the static solution. In particular, the solution type of the lowest energy soliton can change. Our numerical results are of relevance for the quantization of the classical soliton solutions.

We evaluate the modifications to the cosmic microwave background anisotropy spectrum that result from a semiclassical expansion of the Wheeler-DeWitt equation. Recently, such an investigation in the case of a real scalar field coupled to gravity has led to the prediction that the power at large scales is suppressed. We make here a more general analysis and show that there is an ambiguity in the choice of solution to the equations describing the quantum gravitational effects. Whereas one of the two solutions describes a suppression of power, the other one describes an enhancement. We investigate possible criteria for an appropriate choice of solution. The absolute value of the correction term is in both cases of the same order and currently not observable. We also obtain detailed formulas for arbitrary values of a complex parameter occurring in the general solution of the nonlinear equations of the model. We finally discuss the modification of the spectral index connected with the power spectrum and comment on the possibility of a quantum-gravity induced unitarity violation.

Resonant conversion of high energy gravitons into photons in large scale cosmological magnetic fields at the post-recombination epoch is considered. It is shown that the probability of the resonance photon production is much higher than the nonresonant one. As a result, an observable isotropic background of cosmic gamma rays might be created. As shown in our previous paper, an early population of primordial black holes prior to big bang nucleosynthesis could be an efficient source of high frequency gravitational waves. For the primordial black hole mass, about ${10}^8\mathrm{g}$, the produced photons would be the dominant component of the soft to hard cosmic x-ray background and for lower masses the spectrum is shifted down to the ultraviolet and optic.

This paper defines an angular velocity for time-dependent functions on the sphere and applies it to gravitational waveforms from compact binaries. Because it is geometrically meaningful and has a clear physical motivation, the angular velocity is uniquely useful in helping to solve an important—and largely ignored—problem in models of compact binaries: the inverse problem of deducing the physical parameters of a system from the gravitational waves alone. It is also used to define the corotating frame of the waveform. When decomposed in this frame, the waveform has no rotational dynamics and is therefore as slowly evolving as possible. The resulting simplifications lead to straightforward methods for accurately comparing waveforms and constructing hybrids. As formulated in this paper, the methods can be applied robustly to both precessing and nonprecessing waveforms, providing a clear, comprehensive, and consistent framework for waveform analysis. Explicit implementations of all these methods are provided in accompanying computer code.

We study the geodesic motion of massless particles in singly rotating black ring spacetimes. We find stable stationary orbits of massless particles in a toroidal spiral shape in the case that the thickness parameter of a black ring is less than a critical value. Furthermore, there exist nonstationary massless particles bounded in a finite region outside the horizon. This is the first example of stable bound orbits of massless particles around a black object.

Assuming that the observed Higgs-like resonance at the Large Hadron Collider is a technicolor isosinglet scalar (the technicolor Higgs), we argue that the standard model top-induced radiative corrections reduce its mass toward the desired experimental value. We discuss conditions for the spectrum of technicolor theories to feature a technicolor Higgs with the phenomenologically required dynamical mass. We consider different representations under the technicolor gauge group and employ scaling laws in terms of the dimension of the representation. We also summarize the potential effects of walking dynamics on the mass of the technicolor Higgs.

In this paper we perform a comprehensive study of the four $B\to K{\eta }^{(\prime )}$ decays in the perturbative QCD (pQCD) factorization approach. We calculate the $CP$-averaged branching ratios and $CP$-violating asymmetries of $B\to K{\eta }^{(\prime )}$ decays in the ordinary $\eta \mathrm{\text{−}}{\eta }^{\prime }$, the $\eta \mathrm{\text{−}}{\eta }^{\prime }\mathrm{\text{−}}G$, and the $\eta \mathrm{\text{−}}{\eta }^{\prime }\mathrm{\text{−}}G\mathrm{\text{−}}{\eta }_c$ mixing schemes. Besides the full leading order (LO) contributions, all currently known next-to-leading-order (NLO) contributions to $B\to K{\eta }^{(\prime )}$ decays in the pQCD approach are taken into account. From our calculations and phenomenological analysis, we find the following. (a) The NLO contributions in general can provide significant enhancements to the LO pQCD predictions for the decay rates of the two $B\to K{\eta }^{\prime }$ decays, around 70%–89% in magnitude, but result in relatively small changes to $\mathrm{Br}(B\to K\eta )$. (b) Although the NLO pQCD predictions in all three considered mixing schemes agree well with the data within one standard deviation, those pQCD predictions in the $\eta \mathrm{\text{−}}{\eta }^{\prime }\mathrm{\text{−}}G$ mixing scheme provide the best interpretation for the measured pattern of $\mathrm{Br}(B\to K{\eta }^{(\prime )})$: $\mathrm{Br}(B^0\to K^0\eta )\approx 1.13\times {10}^{-6}$, $\mathrm{Br}(B^0\to K^0{\eta }^{\prime })\approx 66.5\times {10}^{-6}$, $\mathrm{Br}(B^{\pm }\to K^{\pm }\eta )\approx 2.36\times {10}^{-6}$, and $\mathrm{Br}(B^{\pm }\to K^{\pm }{\eta }^{\prime })\approx 67.3\times {10}^{-6}$, which agree perfectly with the measured values. (c) The NLO pQCD predictions for the $CP$-violating asymmetries for the four considered decays are also in good agreement with the data. (d) The newly known NLO contribution to the relevant form factors ${\mathcal{M}}_{\mathrm{FF}}$ can produce about a 20% enhancement to the branching ratios $\mathrm{Br}(B\to K{\eta }^{\prime })$, which plays an important role in closing the gap between the pQCD predictions and the relevant data. (e) The general expectations about the relative strength of the LO and NLO contributions from different sources are examined and confirmed by explicit numerical calculations.

We present new measurements of the inclusive forward-backward $t\overline{t}$ production asymmetry, $A_{\mathrm{FB}}$, and its dependence on several properties of the $t\overline{t}$ system. The measurements are performed with the full Tevatron data set recorded with the CDF II detector during $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$, corresponding to an integrated luminosity of $9.4{\mathrm{fb}}^{-1}$. We measure the asymmetry using the rapidity difference $\Delta y=y_t-y_{\overline{t}}$. Parton-level results are derived, yielding an inclusive asymmetry of $0.164\pm 0.047(\mathrm{stat}+\mathrm{syst})$. We establish an approximately linear dependence of $A_{\mathrm{FB}}$ on the top-quark pair mass $M_{t\overline{t}}$ and the rapidity difference $|\Delta y|$ at detector and parton levels. Assuming the standard model, the probabilities to observe the measured values or larger for the detector-level dependencies are $7.4\times {10}^{-3}$ and $2.2\times {10}^{-3}$ for $M_{t\overline{t}}$ and $|\Delta y|$ respectively. Lastly, we study the dependence of the asymmetry on the transverse momentum of the $t\overline{t}$ system at the detector level. These results are consistent with previous lower-precision measurements and provide additional quantification of the functional dependencies of the asymmetry.