We consider gravitational waves from the point of view of both their production and their propagation in doubly coupled bigravity in the metric formalism. In bigravity, the two gravitons are coupled by a nondiagonal mass matrix and show birefrigence. In particular, we find that one of the two gravitons propagates with a speed which differs from one. This deviation is tightly constrained by both the gravitational Cerenkov effect and the energy loss of binary pulsars. When emitted from astrophysical sources, the Jordan frame gravitational wave, which is a linear combination of the two propagating gravitons, has a wave form displaying beats. The best prospect of detecting this phenomenon would come from nano-Hertz interferometric experiments.

Based on the highly improved staggered quark action, we perform lattice simulations of $N_f=8$ QCD and confirm our previous observations, both of a flavor-singlet scalar meson (denoted as $\sigma$) as light as the pion and of various “walking signals” through the low-lying spectra, with higher statistics, smaller fermion masses $m_f$, and larger volumes. We measure $M_{\pi }$, $F_{\pi }$, $M_{\rho }$, $M_{a_0}$, $M_{a_1}$, $M_{b_1}$, $M_N$, $M_{\sigma }$, $F_{\sigma }$, $⟨\overline{\psi }\psi ⟩$ (both directly and through the Gell-Mann-Oakes-Renner relation), and the string tension. The data are consistent with the spontaneously broken phase of the chiral symmetry, in agreement with the previous results: Ratios of the quantities to $M_{\pi }$ monotonically increase in the smaller $m_f$ region towards the chiral limit similarly to $N_f=4$ QCD, in sharp contrast to $N_f=12$ QCD where the ratios become flattened. We perform fits to chiral perturbation theory, with the value of $F_{\pi }$ found in the chiral limit extrapolation reduced dramatically to roughly $2/3$ of the previous result, suggesting the theory is much closer to the conformal window. In fact, each quantity obeys the respective hyperscaling relation throughout a more extensive $m_f$ region compared with earlier works. The hyperscaling relation holds with roughly a universal value of the anomalous dimension, ${\gamma }_m\simeq 1$, with the notable exception of $M_{\pi }$ with ${\gamma }_m\simeq 0.6$ as in the previous results, which reflects the above growing up of the ratios towards the chiral limit. This is a salient feature (walking signal) of $N_f=8$, unlike either $N_f=4$, which has no hyperscaling relation at all, or $N_f=12$ QCD, which exhibits universal hyperscaling. The effective ${\gamma }_m\equiv {\gamma }_m(m_f)$ of $M_{\pi }$ defined for each $m_f$ region has a tendency to grow towards unity near the chiral limit, in conformity with the Nambu-Goldstone boson nature, as opposed to the case of $N_f=12$ QCD where it is almost constant. We further confirm the previous observation of the light $\sigma$ with mass comparable to the pion in the studied $m_f$ region. In a chiral limit extrapolation of the $\sigma$ mass using the dilaton chiral perturbation theory and also using the simple linear fit, we find the value consistent with the 125 GeV Higgs boson within errors. Our results suggest that the theory could be a good candidate for walking technicolor model, having anomalous dimension ${\gamma }_m\simeq 1$ and a light flavor-singlet scalar meson as a technidilaton, which can be identified with the 125 GeV composite Higgs in the $N_f=8$ one-family model.

We determine a new set of parton distribution functions (ABMP16), the strong coupling constant ${\alpha }_s$ and the quark masses $m_c$, $m_b$ and $m_t$ in a global fit to next-to-next-to-leading order (NNLO) in QCD. The analysis uses the $\overline{\mathrm{MS}}$ scheme for ${\alpha }_s$ and all quark masses and is performed in the fixed-flavor number scheme for $n_f=3$, 4, 5. Essential new elements of the fit are the combined data from HERA for inclusive deep-inelastic scattering (DIS), data from the fixed-target experiments NOMAD and CHORUS for neutrino-induced DIS, data from Tevatron and the LHC for the Drell-Yan process and the hadro-production of single-top and top-quark pairs. The theory predictions include new improved approximations at NNLO for the production of heavy quarks in DIS and for the hadro-production of single-top quarks. The description of higher twist effects relevant beyond the leading twist collinear factorization approximation is refined. At NNLO, we obtain the value ${\alpha }_s^{(n_f=5)}(M_Z)=0.1147\pm 0.0008$.

We propose a new method for measuring the top-quark width based on the on-/off-shell ratio of $b$-charge asymmetry in $pp\to Wbj$ production at the LHC. The charge asymmetry removes virtually all backgrounds and related uncertainties, while remaining systematic and theoretical uncertainties can be taken under control by the ratio of cross sections. Limited only by statistical error, in an optimistic scenario, we find that our approach leads to good precision at high integrated luminosity, at a few hundred MeV assuming $300–3000{\mathrm{fb}}^{-1}$ at the LHC. The approach directly probes the total width, in such a way that model-dependence can be minimized. It is complementary to existing cross section measurements which always leave a degeneracy between the total rate and the branching ratio, and provides valuable information about the properties of the top quark. The proposal opens up new opportunities for precision top measurements using a $b$-charge identification algorithm.

The shear viscosity to the entropy density ratio $\eta /s$ of the anisotropic superfluid has been calculated by means of the gauge/gravity duality in the presence of the dark matter sector. The dark matter has been described by the Yang-Mills field analogous to the one describing the visible matter sector, and it is assumed to interact with the visible field with coupling constant $\alpha$. Close to the superfluid transition temperature ($T_c$), the analytical solution has been given up to the leading order in a symmetry breaking parameter and the ratio of the gravitational constant and Yang-Mils coupling. The tensor element of ratio $\eta /s$ remains unaffected by the dark matter for the viscosity tensor in the plane perpendicular to the symmetry breaking direction (here, $yz$). The temperature dependence and the linear correction in ($1-\alpha$) in the plane containing this direction (here, $xy$) was also revealed. The correction linearly vanishes for temperature tending to the critical one $T\to T_c$.

We investigate the proposed duality between a quantum information metric in a ${\mathrm{CFT}}_{d+1}$ and the volume of a maximum time slice in the dual ${\mathrm{AdS}}_{d+2}$ for topological geons. Examining the specific cases of Banados-Teitelboim-Zannelli (BTZ) black holes and planar Schwarzschild–anti-de Sitter black holes, along with their geon counterparts, we find that the proposed duality relation for geons is the same apart from a factor of 4. The information metric therefore provides a probe of the topology of the bulk spacetime.

We consider “twin supergravities”—pairs of supergravities with ${\mathcal{N}}_{+}$ and ${\mathcal{N}}_{-}$ supersymmetries, ${\mathcal{N}}_{+}>{\mathcal{N}}_{-}$, with identical bosonic sectors—in the context of tensoring super Yang-Mills multiplets. It is demonstrated that the pairs of twin supergravity theories are related through their left and right super Yang-Mills factors. This procedure generates new theories from old ones. In particular, the matter coupled ${\mathcal{N}}_{-}$ twins in $D=3$, 5, 6 and the ${\mathcal{N}}_{-}=1$ twins in $D=4$ have not, as far as we are aware, been obtained previously using the double-copy construction, adding to the growing list of double-copy constructible theories. The use of fundamental matter multiplets in the double-copy construction leads us to introduce a bifundamental scalar that couples to the well-known biadjoint scalar field. It is also shown that certain matter coupled supergravities admit more than one factorization into left and right super Yang-Mills-matter theories.

We describe holographic thermal quenches that are inhomogeneous in space. The main characteristic of the quench is to take the system far from its equilibrium configuration. Except in special extreme cases, the problem has no analytic solution. Using the numerical holography methods, we study different observables that measure thermalization such as the time evolution of the apparent horizon, two-point Wightman function and entanglement entropy (EE). Having an extra nontrivial spacial direction allows us to study this peculiar generalization since we categorize the problem based on whether we do the measurements along this special direction or perpendicular to it. Exciting new features that are absent in the common computations appear in the literature; the appearance of negative EE valleys surrounding the positive EE hills and abrupt quenches that occupy the whole space at their universal limit are some of the results of this paper. Physical explanation is given, and connections to Cardy’s idea of thermalization are discussed.

We investigate particle production à la the Schwinger mechanism in an expanding, flat de Sitter patch as is relevant for the inflationary epoch of our Universe. Defining states and particle content in curved spacetime is certainly not a unique process. There being different prescriptions on how that can be done, we have used the Schrödinger formalism to define instantaneous particle content of the state, etc. This allows us to go past the adiabatic regime to which the effect has been restricted in the previous studies and bring out its multifaceted nature in different settings. Each of these settings gives rise to contrasting features and behavior as per the effect of the electric field and expansion rate on the instantaneous mean particle number. We also quantify the degree of classicality of the process during its evolution using a “classicality parameter” constructed out of parameters of the Wigner function to obtain information about the quantum to classical transition in this case.

In the framework of Einstein-Yang-Mills theories, we study the gauge Lorentz group and establish a particular correspondence between this case and a certain class of theories with torsion within Riemann-Cartan space-times. This relation is specially useful in order to simplify the problem of finding exact solutions to the Einstein-Yang-Mills equations. The applicability of the method is divided into two approaches: one associated with the Lorentz group $SO(1,n-1)$ of the space-time rotations, and another one with its subgroup $SO(n-2)$. Solutions for both cases are presented by the explicit use of this correspondence and, interestingly, for the last one by imposing on our ansatz the same kind of rotation and reflection symmetry properties as for a nonvanishing space-time torsion. Although these solutions were found in previous literature by a different approach, our method provides an alternative way to obtain them, and it may be used in future research to find other exact solutions within this theory.

We revisit the computation of maximally winding violating string amplitudes in three-dimensional anti–de Sitter space discussed in Ref. G. Giribet, Violating the string winding number maximally in anti-de Sitter space, Phys. Rev. D 84, 024045 (2011). Here, we give an alternative derivation of these observables. This derivation, the simplest to the best of our knowledge, follows from identities between spectrally flowed representations of $\widehat{sl}(2{)}_k$ Kac-Moody algebra and, in contrast to G. Giribet, Violating the string winding number maximally in anti-de Sitter space, Phys. Rev. D 84, 024045 (2011), it does not resort to conjugate representations with auxiliary fields, but it rather involves the standard Wakimoto free field representation.

We analyze the Galileon ghost condensate implementation of a bouncing cosmological model in the presence of a non-negligible anisotropic stress. We exhibit its structure, which we find to be far richer than previously thought. In particular, even restricting attention to a single set of underlying microscopic parameters, we obtain, numerically, many qualitatively different regimes: depending on the initial conditions on the scalar field leading the dynamics of the Universe, the contraction phase can evolve directly towards a singularity, avoid it by bouncing once, or even bounce many times before settling into an ever-expanding phase. We clarify the behavior of the anisotropies in these various situations.

A Lagrangian formulation of perfect fluid due to a noncanonical three-form field is investigated. The thermodynamic quantities such as energy density, pressure and the four velocity are obtained and then analyzed by comparing with the k-essence scalar field. The nonrelativistic matter due to the generalized three-form field with the equation of state parameter being zero is realized while it might not be possible for the k-essence scalar field. We also found that nonadiabatic pressure perturbations can be possibly generated. The fluid dynamics of the perfect fluid due to the three-form field corresponds to the system in which the number of particles is not conserved. We argue that it is interesting to use this three-form field to represent the dark matter for the classical interaction theory between dark matter and dark energy.

Theoretical models of self-interacting dark matter represent a promising answer to a series of open problems within the so-called collisionless cold dark matter paradigm. In case of asymmetric dark matter, self-interactions might facilitate gravitational collapse and potentially lead to the formation of compact objects predominantly made of dark matter. Considering both fermionic and bosonic (scalar ${\varphi }^4$) equations of state, we construct the equilibrium structure of rotating dark stars, focusing on their bulk properties and comparing them with baryonic neutron stars. We also show that these dark objects admit the $I$-Love-$Q$ universal relations, which link their moments of inertia, tidal deformabilities, and quadrupole moments. Finally, we prove that stars built with a dark matter equation of state are not compact enough to mimic black holes in general relativity, thus making them distinguishable in potential events of gravitational interferometers.

We extend the color glass condensate (CGC) approach to a calculation of the double inclusive gluon production by including the high density effect in the CGC wave function of the projectile (proton). Our main result is that these effects lead to the appearance of odd harmonics in the two particle correlation $C(k,p)$. We find that in the high momentum limit, $|k|,|p|\gg Q_s$, this results in a positive $c_1\{2\}$. Additionally when the magnitudes of the two momenta are approximately equal, $|k|/|p|\approx 1$, the density effects also generate a positive third harmonic $c_3\{2\}$, which translates into a nonvanishing $v_3$ when the momenta of the trigger and an associated particle are in the same momentum bin. The sign of $c_3\{2\}$ becomes negative when $|k|/|p|>1.1$ suggesting an interesting experimental signature.

The low-energy sector of QCD with $N_f=2+1$ dynamical quark flavors at nonvanishing chemical potential and temperature is studied with a nonperturbative functional renormalization group method. The analysis is performed in different truncations in order to explore fluctuation-induced modifications of the quark-meson correlations as well as quark and meson propagators on the chiral phase transition of QCD. Depending on the chosen truncation, significant quantitative implications on the phase transition are found. In the chirally symmetric phase, the quark flavor composition of the pseudoscalar $(\eta ,{\eta }^{\prime })$-meson complex turns out to be drastically sensitive to fluctuation-induced modifications in the presence of the axial $U(1{)}_A$ anomaly. This has important phenomenological consequences for the assignment of chiral partners to these mesons.

A well-studied possibility is that dark matter may reside in a sector secluded from the Standard Model, except for the so-called photon portal: kinetic mixing between the ordinary and dark photons. Such interactions can be probed in dark matter direct detection experiments, and new experimental techniques involving detection of dark matter–electron scattering offer new sensitivity to sub-GeV dark matter. Typically however it is implicitly assumed that the dark matter is not altered as it traverses the Earth to arrive at the detector. In this paper we study in detail the effects of terrestrial stopping on dark photon models of dark matter, and find that they significantly reduce the sensitivity of XENON10 and DAMIC. In particular we find that XENON10 only excludes masses in the range (5–3000) MeV while DAMIC only probes (20–50) MeV. Their corresponding cross section sensitivity is reduced to a window of cross sections between $(5\times {10}^{-38}–{10}^{-30}){\mathrm{cm}}^2$ for XENON10 and a small window around $\sim {10}^{-31}{\mathrm{cm}}^2$ for DAMIC. We also examine implications for a future DAMIC run.

We perform a detailed analysis of dark matter signals of supersymmetric models containing an extra $U(1{)}^{\prime }$ gauge group. We investigate scenarios in which either the right sneutrino or the lightest neutralino are phenomenologically acceptable dark matter candidates and we explore the parameter spaces of different supersymmetric realisations featuring an extra $U(1{)}^{\prime }$. We impose consistency with low energy observables, with known mass limits for the superpartners and $Z^{\prime }$ bosons, as well as with Higgs boson signal strengths, and we moreover verify that predictions for the anomalous magnetic moment of the muon agree with the experimental value and require that the dark matter candidate satisfies the observed relic density and direct and indirect dark matter detection constraints. For the case where the sneutrino is the dark matter candidate, we find distinguishing characteristics among different $U(1{)}^{\prime }$ mixing angles. If the neutralino is the lightest supersymmetric particle, its mass is heavier than that of the light sneutrino in scenarios where the latter is a dark matter candidate, the parameter space is less restricted and differentiation between models is more difficult. We finally comment on the possible collider tests of these models.

Within the extension of MSSM by two right-handed neutrinos, with tree level mass degeneracy, we address the issue of leptogenesis. Investigating the quantum corrections in detail, we show that the lepton asymmetry is induced at the one-loop level and a decisive role is played by the tau lepton Yukawa coupling. On a concrete and predictive neutrino model, which enables us to predict the $CP$ violating $\delta$ phase and relate it to the cosmological $CP$ asymmetry, we demonstrate that the needed amount of the baryon asymmetry is generated via the resonant leptogenesis.