The recent observation of the 750 GeV diphoton excess at 13 TeV LHC has motivated many scenarios of physics beyond the standard model. In this work, we begin by showing that many models which explain the observed excess tend to get strongly coupled well below the Planck scale. We then study a simple scenario involving colored vectorlike fermions with exotic charges, which is expected to stay weakly coupled till the Planck scale. We find the conditions under which this happens, derive the renormalization group equations for such models and solve them to show that perturbativity till Planck scale can be maintained for a very reasonable choice of parameters. Finally, we discuss issues related to vacuum stability and the possibility of inflation in the scenarios we study.

Based on the weakly coupled spontaneous $CP$-violation two-Higgs-doublet model (called the Lee model) and the mechanism to generate the correlation between the smallness of $CP$ violation and the lightness of the scalar mass, as we proposed earlier, we predict a light $CP$ mixing scalar $\eta$ in which the pseudoscalar component is dominant. It is a natural scenario in which $m_{\eta }\sim \mathcal{O}(10\mathrm{GeV})\ll v$. It means new physics might be hidden below the electroweak scale $v$. Masses of all other scalars ($h$, $H$, $H^{\pm }$) should be around the electroweak scale $v$. Among them, the 125 GeV Higgs boson ($h$) couplings are standard-model-like, and the charged Higgs boson ($H^{\pm }$) mass should be around the heaviest neutral scalar ($H$) mass. We discussed all experimental constraints and showed that this scenario is still allowed by data. The strictest constraints come from the flavor violation experiments and the electric dipole moments of the electron and neutron. We also discussed the future tests for this scenario. It is possible to discover the extra scalars or exclude this scenario at future colliders, especially at the LHC and $e^{+}{e}^{-}$ colliders with $\mathcal{O}({\mathrm{ab}}^{-1})$ luminosity. We also pointed out that the $Z$-mediated Higgs pair production via $e^{+}{e}^{-}\to h_i{h}_j$ ($h_i$, $h_j$ stand for two of the $\eta$, $h$, $H$) would be the key observable to confirm or exclude $CP$ violation in the Higgs sector. The sensitivity to test this scenario is worth studying in greater detail.

We determine the renormalization constants for flavor nonsinglet fermion bilinear operators of Möbius domain-wall fermions. The renormalization condition is imposed on the correlation functions in the coordinate space, such that the nonperturbative lattice calculation reproduces the perturbatively calculated counterpart at short distances. The perturbative expansion is precise as the coefficients are available up to $O({\alpha }_s^4)$. We employ $2+1$-flavor lattice ensembles at three lattice spacings in the range 0.044–0.080 fm.

We consider how tetraquarks can affect the chiral phase transition in theories like QCD, with light quarks coupled to three colors. For two flavors the tetraquark field is an isosinglet, and its effect is minimal. For three flavors, however, the tetraquark field transforms in the same representation of the chiral symmetry group as the usual chiral order parameter, and so for very light quarks there may be two chiral phase transitions, which are both of first order. In QCD, results from the lattice indicate that any transition from the tetraquark condensate is a smooth crossover. In the plane of temperature, $T$, and quark chemical potential, $\mu$, a crossover line for the tetraquark condensate is naturally related to the transition line for color superconductivity. We stress that including tetraquarks is essential in using effective models to determine the position of a critical end point in the plane of $T$ and $\mu$. For four flavors we suggest that a triquark field, antisymmetric in both flavor and color, combine to form hexaquarks.

The hadroproduction of the radially excited heavy-quarkonium states $\psi (2S)$ and $\mathrm{\Upsilon }(3S)$ at high energies is studied in the parton Reggeization approach and the factorization formalism of nonrelativistic QCD at lowest order in the strong-coupling constant ${\alpha }_s$ and the relative heavy-quark velocity $v$. A satisfactory description of the $\psi (2S)$ transverse-momentum ($p_T$) distributions measured by ATLAS, CMS, and LHCb at center-of-mass energy $\sqrt{S}=7\mathrm{TeV}$ is obtained using the color-octet long-distance matrix elements (LDMEs) extracted from CDF data at $\sqrt{S}=1.96\mathrm{TeV}$. The importance of the fragmentation mechanism and the scale evolution of the fragmentation functions in the upper $p_T$ range, beyond 30 GeV, is demonstrated. The $\mathrm{\Upsilon }(3S)$ $p_T$ distributions measured by CDF at $\sqrt{S}=1.8\mathrm{TeV}$ and by LHCb at $\sqrt{S}=7\mathrm{TeV}$ and forward rapidities are well described using LDMEs fitted to ATLAS data at $\sqrt{S}=7\mathrm{TeV}$. Comparisons of polarization measurements by CDF and CMS at large $p_T$ values with our predictions consolidate the familiar problem in the $\psi (2S)$ case, but yield reasonable agreement in the $\mathrm{\Upsilon }(3S)$ case.

We present improved perturbative QCD (pQCD) predictions for Higgs boson hadroproduction at the LHC by applying the principle of maximum conformality (PMC), a procedure which resums the pQCD series using the renormalization group (RG), thereby eliminating the dependence of the predictions on the choice of the renormalization scheme while minimizing sensitivity to the initial choice of the renormalization scale. In previous pQCD predictions for Higgs boson hadroproduction, it has been conventional to assume that the renormalization scale ${\mu }_r$ of the QCD coupling ${\alpha }_s({\mu }_r)$ is the Higgs mass and then to vary this choice over the range $1/2m_H<{\mu }_r<2m_H$ in order to estimate the theory uncertainty. However, this error estimate is only sensitive to the nonconformal $\beta$ terms in the pQCD series, and thus it fails to correctly estimate the theory uncertainty in cases where a pQCD series has large higher-order contributions, as is the case for Higgs boson hadroproduction. Furthermore, this ad hoc choice of scale and range gives pQCD predictions which depend on the renormalization scheme being used, in contradiction to basic RG principles. In contrast, after applying the PMC, we obtain next-to-next-to-leading-order RG resummed pQCD predictions for Higgs boson hadroproduction which are renormalization-scheme independent and have minimal sensitivity to the choice of the initial renormalization scale. Taking $m_H=125\mathrm{GeV}$, the PMC predictions for the $pp\to HX$ Higgs inclusive hadroproduction cross sections for various LHC center-of-mass energies are ${\sigma }_{\mathrm{Incl}}{|}_{7\mathrm{TeV}}=21.21_{-1.32}^{+1.36}\mathrm{pb}$, ${\sigma }_{\mathrm{Incl}}{|}_{8\mathrm{TeV}}=27.37_{-1.59}^{+1.65}\mathrm{pb}$, and ${\sigma }_{\mathrm{Incl}}{|}_{13\mathrm{TeV}}=65.72_{-3.01}^{+3.46}\mathrm{pb}$. We also predict the fiducial cross section ${\sigma }_{\mathrm{fid}}(pp\to H\to \gamma \gamma )$: ${\sigma }_{\mathrm{fid}}{|}_{7\mathrm{TeV}}={30.1}_{-2.2}^{+2.3}\mathrm{fb}$, ${\sigma }_{\mathrm{fid}}{|}_{8\mathrm{TeV}}={38.3}_{-2.8}^{+2.9}\mathrm{fb}$, and ${\sigma }_{\mathrm{fid}}{|}_{13\mathrm{TeV}}={85.8}_{-5.3}^{+5.7}\mathrm{fb}$. The error limits in these predictions include the small residual high-order renormalization-scale dependence plus the uncertainty from the factorization scale. The PMC predictions show better agreement with the ATLAS measurements than the LHC Higgs Cross Section Working Group predictions which are based on conventional renormalization-scale setting.

We consider quantum field theoretic systems subject to a time-dependent perturbation, and discuss the question of defining a time-dependent particle number not just at asymptotic early and late times, but also during the perturbation. Naïvely, this is not a well-defined notion for such a nonequilibrium process, as the particle number at intermediate times depends on a basis choice of reference states with respect to which particles and antiparticles are defined, even though the final late-time particle number is independent of this basis choice. The basis choice is associated with a particular truncation of the adiabatic expansion. The adiabatic expansion is divergent, and we show that if this divergent expansion is truncated at its optimal order, a universal time dependence is obtained, confirming a general result of Dingle and Berry. This optimally truncated particle number provides a clear picture of quantum interference effects for perturbations with nontrivial temporal substructure. We illustrate these results using several equivalent definitions of adiabatic particle number: the Bogoliubov, Riccati, spectral function and Schrödinger picture approaches. In each approach, the particle number may be expressed in terms of the tiny deviations between the exact and adiabatic solutions of the Ermakov-Milne equation for the associated time-dependent oscillators.

We extend the loop quantum cosmology matter bounce scenario in order to include a dark energy era, which ends abruptly at a rip singularity where the scale factor and the Hubble rate diverge. In the “deformed matter bounce scenario,” the Universe is contracting from an initial noncausal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, and thus the model is described by a dark energy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the dark energy era is quintessential as what follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the dark energy era, a rip singularity exists, where the scale factor and Hubble rate diverge; however, the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, first that the ordinary loop quantum cosmology matter bounce evolution stops, thus ending the infinite repetition of the ordinary matter bounce scenario. Second, the fact that both the pressure and the density become complex probably indicates that the description of the cosmic evolution within the theoretical context of loop quantum cosmology ceases to describe the physics of the system and possibly a more fundamental theory of quantum gravity is needed near the would be rip singularity. We describe the qualitative features of the model, and we also investigate how this cosmology could be realized by a viscous fluid in the context of loop quantum cosmology. In addition to this, we show how this deformed model can be realized by a canonical scalar field filled Universe, in the context of loop quantum cosmology. Finally, we demonstrate how the model can be generated by a vacuum $F(R)$ gravity.

The Immirzi parameter is promoted to be a scalar field and the Hamiltonian analysis of the corresponding dynamical system is performed in the presence of gravity. We identified some $SU(2)$ connections, generalizing Ashtekar-Barbero variables, and we rewrite the constraints in terms of them, setting the classical formulation suitable for loop quantization. Then, we consider the reduced system obtained when restricting to a flat isotropic cosmological model. By mimicking loop quantization via an effective semiclassical treatment, we outline how quantum effects are able to tame the initial singularity both in synchronous time and when the Immirzi field is taken as a relational time.

Up to hundreds of black hole binaries individually resolvable by eLISA will coalesce in the Advanced LIGO and Virgo band within 10 yr, allowing for multiband gravitational wave observations. Binaries formed via dynamical interactions in dense star clusters are expected to have eccentricities $e_0\sim {10}^{-3}-{10}^{-1}$ at the frequencies $f_0={10}^{-2}\mathrm{Hz}$ where eLISA is most sensitive, while binaries formed in the field should have negligible eccentricity in both frequency bands. We estimate that eLISA should always be able to detect a nonzero $e_0$ whenever $e_0\gtrsim {10}^{-2}$; if $e_0\sim {10}^{-3}$, eLISA should detect nonzero eccentricity for a fraction $\sim 90\%$ ($\sim 25\%$) of binaries when the observation time is $T_{\mathrm{obs}}=5$ (2) yr, respectively. Therefore eLISA observations of black hole binaries have the potential to distinguish between field and cluster formation scenarios.

For a conformally coupled scalar field we obtain the conformally related Einstein-Langevin equations, using appropriate transformations for all the quantities in the equations between two conformally related spacetimes. In particular, we analyze the transformations of the influence action, the stress energy tensor, the noise kernel and the dissipation kernel. In due course the fluctuation-dissipation relation is also discussed. The analysis in this paper thereby facilitates a general solution to the Einstein-Langevin equation once the solution of the equation in a simpler, conformally related spacetime is known. For example, from the Minkowski solution of Martín and Verdaguer, those of the Einstein-Langevin equations in conformally flat spacetimes, especially for spatially flat Friedmann-Robertson-Walker models, can be readily obtained.

The theory of nonexpanding horizons (NEHs) geometry and the theory of near-horizon geometries (NHGs) are two mathematical relativity frameworks generalizing the black hole theory. From the point of view of the NEHs theory, a NHG is just a very special case of a spacetime containing a NEH of many extra symmetries. It can be obtained as the Horowitz limit of a neighborhood of an arbitrary extremal Killing horizon. An unexpected relation between the two of them was discovered in the study of spacetimes foliated by a family of NEHs. The class of four-dimensional NHG solutions (either vacuum or coupled to a Maxwell field) was found as a family of examples of spacetimes admitting a NEH foliation. In the current paper, we systematically investigate geometries of the NEHs foliating a spacetime for arbitrary matter content and in arbitrary spacetime dimensions. We find that each horizon belonging to the foliation satisfies a condition that may be interpreted as an invitation for a transversal NEH to exist and to admit the structure of an extremal isolated horizon. Assuming the existence of a transversal extremal isolated horizon, we derive all the spacetime metrics satisfying the vacuum Einstein’s equations. In this case, the NEHs become bifurcated Killing horizons.

We show that gravitational wave radiative patterns from a point test particle falling radially into a Schwarzschild black hole, as derived by Davis, Ruffini, Press and Price [M. Davis et al., Phys. Rev. Lett. 27, 1466 (1971).], are present in the nonlinear regime of head-on mergers of black holes. We use the Bondi-Sachs characteristic formulation and express the gravitational wave luminosity and the net momentum flux in terms of the news functions. We then evaluate the ($-2$)-spin-weighted $\ell$-multipole decomposition of these quantities via exact expressions valid in the nonlinear regime and defined at future null infinity. Our treatment is made in the realm of Robinson-Trautman dynamics, with characteristic initial data corresponding to the head-on merger of two black holes. We consider mass ratios in the range $0.01\le \alpha \le 1$. We obtain the exponential decay with $\ell$ of the total energy contributed by each multipole $\ell$, with an accurate linear correlation in the log-linear plot of the points up to $\alpha \simeq 0.7$. Above this mass ratio the contribution of the odd modes to the energy decreases faster than that of the even modes, leading to the breaking of the linear correlation; for $\alpha =1$ the energy in all odd modes is zero. The dominant contribution to the total radiated energy comes from the quadrupole mode $\ell =2$ corresponding, for instance, to about $\simeq 84\%$ for small mass ratios up to $\simeq 99.8\%$ for the limit case $\alpha =1$. The total rescaled radiated energy $E_W^{\text{total}}/m_0{\alpha }^2$ decreases linearly with decreasing $\alpha$, yielding for the point particle limit $\alpha \to 0$ the value $\simeq 0.0484$, about 5 times larger than the result of Davis et al. [1]. The mode decomposition of the net momentum flux and of the associated gravitational wave impulses results in an adjacent-even-odd mode-mixing pattern. We obtain that the impulses contributed by each $(\ell ,\ell +1)$ mixed mode also accurately satisfy the exponential decay with $\ell$, for the whole mass ratio domain considered, $0.01\le \alpha <1$. The (2, 3) mode contributions to the total impulses are dominant. The mode-mixing effect can also be seen in the decomposition of the net kick velocity imparted to the system by the gravitational wave emission. The mixed mode impulses reach a maximum at $\alpha \simeq 0.7$; for $\alpha >0.7$ the impulses decrease and are zero in the equal mass case, due to the decrease to zero of the odd modes of the news functions.

Cosmology in Eddington-inspired Born-Infeld gravity is investigated using a scalar Born-Infeld field (e.g. tachyon condensate) as matter. In this way, both in the gravity and matter sectors we have Born-Infeld-like structures characterized by their actions and via two separate constants, $\kappa$ and ${\alpha }_T^2$, respectively. With a particular choice of the form of $\dot{\varphi }$ (the time derivative of the Born-Infeld scalar), analytical cosmological solutions are found. Thereafter, we explore some of the unique features of the corresponding cosmological spacetimes. For $\kappa >0$, our solution has a de Sitter-like expansion both at early and late times, with an intermediate deceleration sandwiched between the accelerating phases. On the other hand, when $\kappa <0$, the initial de Sitter phase is replaced by a bounce. Our solutions, at late time, fit well with available supernova data—a fact we demonstrate explicitly. The estimated properties of the Universe obtained from the fitting of the $\kappa >0$ solution are as good as in $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. However, the $\kappa <0$ solution has to be discarded due to the occurrence of a bounce at an unacceptably low redshift.

Dark matter annihilation or decay could have a significant impact on the ionization and thermal history of the universe. In this paper, we study the potential contribution of dark matter annihilation ($s$-wave- or $p$-wave-dominated) or decay to cosmic reionization, via the production of electrons, positrons and photons. We map out the possible perturbations to the ionization and thermal histories of the universe due to dark matter processes, over a broad range of velocity-averaged annihilation cross sections/decay lifetimes and dark matter masses. We have employed recent numerical studies of the efficiency with which annihilation/decay products induce heating and ionization in the intergalactic medium, and in this work extended them down to a redshift of $1+z=4$ for two different reionization scenarios. We also improve on earlier studies by using the results of detailed structure formation models of dark matter haloes and subhaloes that are consistent with up-to-date $N$-body simulations, with estimates on the uncertainties that originate from the smallest scales. We find that for dark matter models that are consistent with experimental constraints, a contribution of more than 10% to the ionization fraction at reionization is disallowed for all annihilation scenarios. Such a contribution is possible only for decays into electron/positron pairs, for light dark matter with mass $m_{\chi }\lesssim 100\mathrm{MeV}$, and a decay lifetime ${\tau }_{\chi }\sim 10^{24}–10^{25}\mathrm{s}$.

We consider an extension of the Standard Model with a singlet sector consisting of a real (pseudo)scalar and a Dirac fermion coupled with the Standard Model only via the scalar portal. We assume that the portal coupling is weak enough for the singlet sector not to thermalize with the Standard Model allowing the production of singlet particles via the freeze-in mechanism. If the singlet sector interacts with itself sufficiently strongly, it may thermalize within itself, resulting in dark matter abundance determined by the freeze-out mechanism operating within the singlet sector. We investigate this scenario in detail. In particular, we show that requiring the absence of inflationary isocurvature fluctuations provides lower bounds on the magnitude of the dark sector self-interactions and in parts of the parameter space favors sufficiently large self-couplings, supported also by the features observed in the small-scale structure formation.

We propose a formalism for the analysis of direct-detection dark-matter searches that covers all coherent responses for scalar and vector interactions and incorporates QCD constraints imposed by chiral symmetry, including all one- and two-body WIMP-nucleon interactions up to third order in chiral effective field theory. One of the free parameters in the WIMP-nucleus cross section corresponds to standard spin-independent searches, but in general different combinations of new-physics couplings are probed. We identify the interference with the isovector counterpart of the standard spin-independent response and two-body currents as the dominant corrections to the leading spin-independent structure factor, and discuss the general consequences for the interpretation of direct-detection experiments, including minimal extensions of the standard spin-independent analysis. Fits for all structure factors required for the scattering off xenon targets are provided based on state-of-the-art nuclear shell-model calculations.

Fermi-LAT observations of the Milky Way Galactic Center (GC) have revealed a spherically symmetric excess of GeV $\gamma$ rays extending to at least 10° from the dynamical center of the Galaxy. A critical uncertainty in extracting the intensity, spectrum, and morphology of this excess concerns the accuracy of astrophysical diffuse $\gamma$-ray emission models near the GC. Recently, it has been noted that many diffuse emission models utilize a cosmic-ray injection rate far below that predicted based on the observed star-formation rate in the Central Molecular Zone. In this study, we add a cosmic-ray injection component which nonlinearly traces the Galactic ${\mathrm{H}}_2$ density determined in three dimensions, and find that the associated $\gamma$-ray emission is degenerate with many properties of the GC $\gamma$-ray excess. Specifically, in models that utilize a large sideband ($40°\times 40°$ surrounding the GC) to normalize the best-fitting diffuse emission models, the intensity of the GC excess decreases by approximately a factor of 2, and the morphology of the excess becomes less peaked and less spherically symmetric. In models which utilize a smaller region of interest ($15°\times 15°$) the addition of an excess template instead suppresses the intensity of the best-fit astrophysical diffuse emission, and the GC excess is rather resilient to changes in the details of the astrophysical diffuse modeling. In both analyses, the addition of a GC excess template still provides a statistically significant improvement to the overall fit to the $\gamma$-ray data. We also implement advective winds at the GC, and find that the Fermi-LAT data strongly prefer outflows of order several hundred km/s, whose role is to efficiently advect low-energy cosmic rays from the inner-few kpc of the Galaxy. Finally, we perform numerous tests of our diffuse emission models, and conclude that they provide a significant improvement in the physical modeling of the multiwavelength nonthermal emission from the GC region.

Scalar particles are a common prediction of many beyond the Standard Model theories. If they are light and cold enough, there is a possibility they may form Bose-Einstein condensates, which will then become gravitationally bound. These boson stars are solitonic solutions to the Einstein-Klein-Gordon equations but may be approximated in the nonrelativistic regime with a coupled Schrödinger-Poisson system. General properties of single soliton states are derived, including the possibility of quartic self-interactions. Binary collisions between two solitons are then studied, and the effects of different mass ratios, relative phases, self-couplings, and separation distances are characterized, leading to an easy conceptual understanding of how these parameters affect the collision outcome in terms of conservation of energy. Applications to dark matter are discussed.

Relativistic Bose-Einstein condensates (rBECs) have recently become a well-established system for analogue gravity. Indeed, while such relativistic systems cannot be yet realized experimentally, they provide an interesting framework for mimicking metrics for which no analogue is yet available, thus paving the way for further theoretical and numerical explorations. In this vein, we here discuss black holes in rBECs and explore how their features relate to the bulk properties of the system. We then propose the coupling of external fields to the rBEC as a way to mimic nonmetric features. In particular, we use a Proca field to simulate an aether field, as found in Einstein-aether or Hořava-Lifshitz gravity. This allows us to mimic a universal horizon, the causal barrier relevant for superluminal modes in these modified gravitational theories.