The concordance model of cosmology favors a universe with a tiny positive cosmological constant. A tiniest positive constant curvature profoundly alters the asymptotic structure, forcing a relook at a theory of gravitational radiation. Even for compact astrophysical sources, the intuition from Minkowski background is challenged at every step. Nevertheless, at least for candidate sources such as compact binaries, it is possible to quantify the influence of the cosmological constant, as small corrections to the leading order Minkowski background results. Employing suitably chosen Fermi normal coordinates in the static patch of the de Sitter background, we compute the field due to a compact source to first order in $\mathrm{\Lambda }$. For contrast, we also present the field in the Poincaré patch where the leading correction is of order $\sqrt{\mathrm{\Lambda }}$. We introduce a gauge invariant quantity, deviation scalar, containing polarization information and compute it in both charts for a comparison.

In this paper, we show that there exists a class of dilaton models with nontrivial scalar-Ricci and scalar-matter couplings that strongly reduces observational deviations from general relativity in the dust limit. Essentially, depending on the coupling between the dilaton and the fundamental matter fields, various strengths of decoupling can appear. They range from no decoupling at all to a total decoupling state. In this latter case, the theory becomes indistinguishable from general relativity (in the dust limit), as all dilatonic effects can be reabsorbed through a simple change of unit. Furthermore, for particular decouplings, we show that the phenomenology used to constrain theories from the universality of free fall observations is significantly different from what is commonly used. Finally, from a fundamental perspective, the class of nondynamical decouplings proposed in this paper might play a role in the current nonobservation of any deviation from general relativity (in both tests of the equivalence principle and of the parametrized post-Newtonian formalism).

We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic models, because for all simulations—including sources with two independent, precessing spins—we perform comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported by Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)] (at the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing simulations. Follow-up simulations performed using previously estimated binary parameters most resemble the data, even when all quadrupolar and octopolar modes are included. Comparisons including only the quadrupolar modes constrain the total redshifted mass $M_z\in [64M_{\odot }-82M_{\odot }]$, mass ratio $1/q=m_2/m_1\in [0.6,1]$, and effective aligned spin ${\chi }_{\mathrm{eff}}\in [-0.3,0.2]$, where ${\chi }_{\mathrm{eff}}=({\mathbf{S}}_1/m_1+{\mathbf{S}}_2/m_2)·\widehat{\mathbf{L}}/M$. Including both quadrupolar and octopolar modes, we find the mass ratio is even more tightly constrained. Even accounting for precession, simulations with extreme mass ratios and effective spins are highly inconsistent with the data, at any mass. Several nonprecessing and precessing simulations with similar mass ratio and ${\chi }_{\mathrm{eff}}$ are consistent with the data. Though correlated, the components’ spins (both in magnitude and directions) are not significantly constrained by the data: the data is consistent with simulations with component spin magnitudes $a_{1,2}$ up to at least 0.8, with random orientations. Further detailed follow-up calculations are needed to determine if the data contain a weak imprint from transverse (precessing) spins. For nonprecessing binaries, interpolating between simulations, we reconstruct a posterior distribution consistent with previous results. The final black hole’s redshifted mass is consistent with $M_{f,z}$ in the range $64.0M_{\odot }-73.5M_{\odot }$ and the final black hole’s dimensionless spin parameter is consistent with $a_f=0.62–0.73$. As our approach invokes no intermediate approximations to general relativity and can strongly reject binaries whose radiation is inconsistent with the data, our analysis provides a valuable complement to Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)].

We study the production of light particles due to the oscillation of the Hubble parameter or the scale factor. Any coherently oscillating scalar field, irrespective of its energy fraction in the Universe, imprints such an oscillating feature on them. Not only Einstein gravity but the extended gravity models, such as models with nonminimal (derivative) coupling to gravity and $f(R)$ gravity, lead to oscillation of the scale factor. We present a convenient way to estimate the gravitational particle production rate in these circumstances. Cosmological implications of gravitational particle production, such as dark matter/radiation and moduli problem, are discussed. For example, if the theory is described solely by the standard model plus the Peccei-Quinn sector, the Starobinsky $R^2$ inflation may lead to an observable amount of axion dark radiation.

We study bounds from perturbative unitarity in a composite two-Higgs doublet model (C2HDM) based on the spontaneous breakdown of a global symmetry $SO(6)\to SO(4)\times SO(2)$ at the compositeness scale $f$. The eight pseudo-Nambu-Goldstone bosons (pNGBs) emerging from such a dynamics are identified as two isospin doublet Higgs fields. We calculate the $S$-wave amplitude for all possible two-to-two-body elastic (pseudo)scalar boson scatterings at energy scales $\sqrt{s}$ reachable at the Large Hadron Collider (LHC) and beyond it, including the longitudinal components of weak gauge boson states as the corresponding pNGB states. In our calculation, the Higgs potential is assumed to have the same form as that in the elementary two-Higgs doublet model (E2HDM) with a discrete $Z_2$ symmetry, which is expected to be generated at the one-loop level via the Coleman-Weinberg mechanism. We find that the $S$-wave amplitude matrix can be block-diagonalized with maximally $2\times 2$ submatrices in a way similar to the E2HDM case as long as we only keep the contributions from $\mathcal{O}(\xi s)$ and $\mathcal{O}({\xi }^0{s}^0)$ in the amplitudes, where $\xi =v_{\mathrm{SM}}^2/f^2$ and $v_{\mathrm{SM}}\simeq 246\mathrm{GeV}$, which is an appropriate approximation for our analysis. By requiring the C2HDM to satisfy perturbative unitarity at energies reachable by the LHC, we derive bounds on its parameters such as $\xi$ and the masses of extra Higgs bosons present in the scenario alongside the Standard Model-like Higgs state discovered in 2012.

The dead cone is a well-known effect in gauge theories, where radiation from a charged particle of mass $m$ and energy $E$ is suppressed within an angular size of $m/E$. This effect is universal as it does not depend on the spin of the particle nor on the nature of the gauge interaction. It is challenging to directly measure the dead cone at colliders, however, since the region of suppressed radiation either is too small to be resolved or is filled by the decay products of the massive particle. In this paper, we propose to use jet substructure techniques to expose the dead cone effect in the strong-force radiation pattern around boosted top quarks at the Large Hadron Collider. Our study shows that with $300/\mathrm{fb}$ of 13–14 TeV collision data, ATLAS and CMS could obtain the first direct evidence of the dead cone effect and test its basic features.

We study the effects of a parity-odd “odderon” correlation in Jalilian-Marian–Iancu–McLerran–Weigert–Leonidov–Kovner renormalization group evolution at high energy. Firstly we show that in the eikonal picture where the scattering is described by Wilson lines, one obtains a strict mathematical upper limit for the magnitude of the odderon amplitude compared to the parity-even Pomeron one. This limit increases with $N_{\mathrm{c}}$, approaching infinity in the infinite $N_{\mathrm{c}}$ limit. We use a systematic extension of the Gaussian approximation including both two- and three-point correlations which enables us to close the system of equations even at finite $N_{\mathrm{c}}$. In the large-$N_{\mathrm{c}}$ limit we recover an evolution equation derived earlier. By solving this equation numerically we confirm that the odderon amplitude decreases faster in the nonlinear case than in the linear Balitsky-Fadin-Kuraev-Lipatov limit. We also point out that, in the three-point truncation at finite $N_{\mathrm{c}}$, the presence of an odderon component introduces azimuthal angular correlations $\sim \cos (n\phi )$ at all $n$ in the target color field. These correlations could potentially have an effect on future studies of multiparticle angular correlations.

The consistency of the embedding of four-dimensional $SO(8)$ gauged $\mathcal{N}=8$ supergravity into eleven-dimensional supergravity, where the internal directions are compactified on a seven-sphere, was established by de Wit and Nicolai in the 1980s. The reduction Ansatz for the eleven-dimensional metric, and for some of the components of the 4-form field strength, were found at that time, and recently the complete expression for the 4-form reduction has been obtained. The expressions are quite complicated, and in many practical applications it would be sufficient to know the Ansatz for a subset of the four-dimensional fields. In this paper, we obtain explicit expressions for the embedding of the truncation of the full $\mathcal{N}=8$ gauged theory to the $\mathcal{N}=2$ gauged STU supergravity. This corresponds, in the bosonic sector, to a consistent truncation of the $\mathcal{N}=8$ supergravity fields to those that are singlets under the $U(1{)}^4$ Cartan subalgebra of $SO(8)$. This truncation to STU supergravity, which comprises $\mathcal{N}=2$ supergravity coupled to three vector multiplets, suffices, for example, for lifting the general 8-charge asymptotically anti–de Sitter rotating black holes to eleven dimensions. We also give two distinct further truncations to $\mathcal{N}=2$ supergravities coupled to single vector multiplets.

We argue that extra dimensions with a properly chosen compactification scheme could be a natural source for emergent gauge symmetries. Actually, some proposed vector field potential terms or polynomial vector field constraints introduced in five-dimensional Abelian and non-Abelian gauge theory are shown to smoothly lead to spontaneous violation of an underlying 5D spacetime symmetry and generate pseudo-Goldstone vector modes as conventional 4D gauge boson candidates. As a special signature, there appear, apart from conventional gauge couplings, some properly suppressed direct multiphoton (multiboson, in general) interactions in emergent QED and Yang-Mills theories whose observation could shed light on their high-dimensional nature. Moreover, in emergent Yang-Mills theories an internal symmetry $G$ also occurs spontaneously broken to its diagonal subgroups once 5D Lorentz violation happens. This breaking originates from the extra vector field components playing a role of some adjoint scalar field multiplet in the 4D spacetime. So, one naturally has the Higgs effect without a specially introduced scalar field multiplet. Remarkably, when being applied to grand unified theories (GUTs) this results in a fact that the emergent GUTs generically appear broken down to the Standard Model just at the 5D Lorentz violation scale $M$.

Anomaly-free perturbations of loop quantum cosmology with holonomy corrections reveal an $\mathrm{\Omega }$-deformed spacetime structure, $\mathrm{\Omega }≔1-2\rho /{\rho }_c$, where $\mathrm{\Omega }<0$ indicates a Euclidean-like space and $\mathrm{\Omega }>0$ indicates a Lorentz-like space. It would be reasonable to give the initial value at the spacetime transition point, $\rho ={\rho }_c/2$, but we find that it is impossible to define a Minkowski-like vacuum even for large $k$ modes at that time. However, if we loosen the condition and give the initial value slightly after $\mathrm{\Omega }=0$, e.g., $\mathrm{\Omega }\simeq 0.2$, the vacuum state can be well defined and, furthermore, the slow roll approximation also works well in that region. Both scalar and tensor spectra are considered in the framework of loop quantum cosmology with holonomy corrections. We find that, if the energy density is not too small in relation to ${\rho }_c/2$ when the considered $k$ mode crossing the horizon, effective theory can give a much smaller scalar power spectrum than classical theory and the spectrum of tensor perturbations could blueshift. However, when compared to other observations, since the energy densities when the modes crossed the horizon were significantly smaller than ${\rho }_c$, the results we get agree with previous work in the literature and with the classical inflation theory.

In this work, we use a dynamical system approach to analyze the viability of $f(R,\mathcal{L})$ candidates for dark energy. We compare these with nonminimal coupled $f(R)$ theories and study the solutions for exponential and power-law forms in order to constrain the allowed range of model parameters.

In a previous work [S. Rahbardehghan and H. Pejhan, Phys. Lett. B 750, 627 (2015)], we considered a simple brane-world model: a single four-dimensional brane embedded in a five-dimensional de Sitter (dS) space-time. Then, by including a conformally coupled scalar field in the bulk, we studied the induced Casimir energy-momentum tensor. Technically, the Krein-Gupta-Bleuler quantization scheme as a covariant and renormalizable quantum field theory in dS space was used to perform the calculations. In the present paper, we generalize this study to a less idealized, but physically motivated, scenario; namely, we consider Friedmann-Robertson-Walker (FRW) space-time which behaves asymptotically as a dS space-time. More precisely, we evaluate a Casimir energy-momentum tensor for a system with two $D$-dimensional curved branes on background of $D+1$-dimensional FRW space-time with negative spatial curvature and a conformally coupled bulk scalar field that satisfied the Dirichlet boundary condition on the branes.

The gravitational wave signal GW150914, recently detected by LIGO and Virgo collaborations, is used to place a bound on the scale of quantum fuzziness of noncommutative space-time. We show that the leading noncommutative correction to the phase of the gravitational waves produced by a binary system appears at the second order of the post-Newtonian expansion. This correction is proportional to ${\mathrm{\Lambda }}^2\equiv |{\theta }^{0i}{|}^2/(l_P{t}_P{)}^2$, where ${\theta }^{\mu \nu }$ is the antisymmetric tensor of noncommutativity. To comply with GW150914 data, we find that $\sqrt{\mathrm{\Lambda }}\lesssim 3.5$, namely at the order of the Planck scale. This is the most stringent bound on the noncommutative scale, exceeding the previous constraints from particle physics processes by $\sim 15$ orders of magnitude.

We study quantum mechanical tunneling using complex solutions of the classical field equations. Simple visualization techniques allow us to unify and generalize previous treatments, and straightforwardly show the connection to the standard approach using Euclidean instanton solutions. We demonstrate that the negative modes of solutions along various contours in the complex time plane reveal which paths give the leading contribution to tunneling and which do not, and we provide a criterion for identifying the negative modes. Central to our approach is the solution of the background and perturbation equations not only along a single path, but over an extended region of the complex time plane. Our approach allows for a fully continuous and coherent treatment of classical evolution interspersed by quantum tunneling events and is applicable in situations where singularities are present and also where Euclidean solutions might not exist.

We reinvestigate gravitational ellipsoidal collapse with special focus on its impact on primordial black hole formation. We start with the results for the collapse threshold in the case of ellipsoidal collapse in the context of structure formation, and show heuristically that a similar functional form for the threshold should be expected in the case of primordial black hole formation. For a generic model we apply this to demonstrate that the abundance and energy density of the produced primordial black holes can be significantly decreased when the nonsphericity of the overdensities is taken into account. Further numerical study of this phenomenon may be crucial in order to produce reliable predictions for primordial black hole abundances from inflationary models.

We study the nature of potentials in scalar field based models for dark energy—with both canonical and noncanonical kinetic terms. We calculate numerically, and using an analytic approximation around $a\approx 1$, potentials for models with constant equation-of-state parameter $w_{\varphi }$. We find that for a wide range of models with canonical and noncanonical kinetic terms there is a simple approximation for the potential that holds when the scale factor is in the range $0.6\lesssim a\lesssim 1.4$. We discuss how this form of the potential can also be used to represent models with nonconstant $w_{\varphi }$ and, hence, how it could be used in reconstruction from cosmological data.

One of the possible sources of hadronic cosmic rays (CRs) are newborn pulsars. If this is indeed the case, they should feature diffusive gamma-ray halos produced by interactions of CRs with interstellar gas. In this paper we try to identify extended gamma-ray emission around young pulsars, making use of the 7-year Fermi-LAT data. For this purpose we select and analyze a set of eight pulsars that are most likely to possess detectable gamma-ray halos. We find extended emission that might be interpreted as a gamma-ray halo only in the case of PSR $\mathrm{J}0007+7303$. Its luminosity accords with the total energy of injected cosmic rays $\sim 10^{50}\mathrm{erg}$, although other interpretations of this source are possible. Irrespectively of the nature of this source, we put bounds on the luminosity of gamma-ray halos which suggest that pulsars’ contribution to the overall energy budget of galactic CRs is subdominant in the GeV–TeV range.

A general consensus now is that there are two physically inequivalent complete decompositions of the nucleon spin, i.e. the decomposition of the canonical type and that of mechanical type. The well-known Jaffe-Manohar decomposition is of the former type. Unfortunately, there is a wide-spread misbelief that this decomposition matches the partonic picture, which states that motion of quarks in the nucleon is approximately free. In the present monograph, we reveal that this understanding is not necessarily correct and that the Jaffe-Manohar decomposition is not such a decomposition, which natively reflects the intrinsic (or static) orbital angular momentum structure of the nucleon.

This work deals with the right-handed sneutrino as thermal cold dark matter candidate. This scalar emerges in a supersymmetric version of the $SU(3{)}_c\otimes SU(3{)}_L\otimes U(1{)}_X$ gauge model where right-handed neutrinos are a natural component of leptonic chiral scalar supermultiplets. We first consider the issue of a 125 GeV Higgs boson mass in this model, showing that constraints on the stop mass and trilinear soft coupling are considerably alleviated compared to the minimal supersymmetric standard model. Then, we investigate the region of parameter space that is consistent with right-handed sneutrino as thermal cold dark matter, under the light of Planck results on the relic abundance and direct detection from the LUX experiment. This sneutrino mainly annihilates through an extra neutral gauge boson, $Z^{\prime }$, and Higgs exchange so that the physics of dark matter is somewhat related to the parameters determining Higgs and $Z^{\prime }$ masses. We then obtain that the right-handed sneutrino in this model must be heavier than 400 GeV to conform with Planck and LUX, simultaneously constraining the $Z^{\prime }$ mass to be above 2400 GeV, which is in perfect agreement with LHC searches in a nonsupersymmetric version of this model.