We present results on the quark unpolarized, helicity and transversity parton distributions functions of the nucleon. We use the quasiparton distribution approach within the lattice QCD framework and perform the computation using an ensemble of twisted mass fermions with the strange and charm quark masses tuned to approximately their physical values and light quark masses giving pion mass of 260 MeV. We use hierarchical probing to evaluate the disconnected quark loops. We discuss identification of ground state dominance, the Fourier transform procedure and convergence with the momentum boost. We find nonzero results for the disconnected isoscalar and strange quark distributions. The determination of the quark parton distribution and in particular the strange quark contributions that are poorly known provide valuable input to the structure of the nucleon.

We discuss transverse momentum dependent (TMD) gluon distributions within high energy factorization at next-to-leading order in the strong coupling within the framework of Lipatov’s high energy effective action. We provide a detailed discussion of both rapidity divergences related to the TMD definition and its soft factor on the one hand, and rapidity divergences due to high energy factorization on the other hand, and discuss common features and differences between Collins-Soper (CS) and Balitsky-Fadin-Kuarev-Lipatov (BFKL) evolution. While we confirm earlier results which state that the unpolarized and linearly polarized gluon TMD agree in the BFKL limit at leading order, we find that both distributions differ, once next-to-leading order corrections are being included. Unlike previous results, our framework allows us to recover the complete anomalous dimension associated with the Collins-Soper-Sterman (CSS) evolution of the TMD distribution, including also single-logarithmic terms in the CSS evolution. As an additional result, we provide a definition of $k_T$ factorization, i.e., matching of off shell coefficients to collinear factorization at next-to-leading order within high energy factorization and the effective action framework. We furthermore establish a link between the QCD operator definition of the TMD gluon distribution and a previously derived off shell TMD gluon-to-gluon splitting function, which is within the present framework obtained as the real one-loop correction.

We outline a strategy of how to search for QCD instantons of invariant mass 20–60 GeV in diffractive events in low-luminosity runs at the LHC. We show that, by imposing appropriate selection criteria on the final states, one can select the kinematic regime where the instanton signal exceeds the background by a factor of at least 8. In spite of the relatively strong cuts that we impose on the total transverse energy and the number of charged tracks, ${\sum }_i{E}_{T,i}>15\mathrm{GeV}$ and $N_{\mathrm{ch}}>20$ measured within the $0<\eta <2$ interval and excluding events with high-$p_T$ particles, the expected cross section is sufficiently large to study the instanton production in events with large rapidity gaps at low luminosities, thus avoiding problems with pileup. The paper also includes an updated computation of instanton cross sections and other parameters relevant for ongoing studies.

Chiral effective theory of scalar and vector diquarks is formulated according to the linear sigma model. The main application is to describe the ground and excited states of singly heavy baryons with a charm or bottom quark. Applying the potential quark model between the diquark and the heavy quark ($Q=c$, $b$), we construct a heavy-quark–diquark model. The spectra of the positive- and negative-parity states of ${\mathrm{\Lambda }}_Q$, ${\mathrm{\Sigma }}_Q$, ${\mathrm{\Xi }}_Q^{{(}^{\prime })}$, and ${\mathrm{\Omega }}_Q$ are obtained. The masses and interaction parameters of the effective theory are fixed partly from the lattice QCD data and also from fitting low-lying heavy-baryon masses. We find that the negative parity excited states of ${\mathrm{\Xi }}_Q$ (flavor $\overline{\mathbf{3}}$) are different from those of ${\mathrm{\Lambda }}_Q$, because of the inverse hierarchy of the pseudoscalar diquark. On the other hand, ${\mathrm{\Sigma }}_Q$, ${\mathrm{\Xi }}_Q^{\prime }$, and ${\mathrm{\Omega }}_Q$ (flavor $\mathbf{6}$) baryons have similar spectra. We compare our results of the heavy-quark–diquark model with experimental data as well as the quark model.

We employ a nonequilibrium quantum chromodynamics kinetic description to study the kinetic and chemical equilibration of the quark-gluon plasma at weak coupling. Based on our numerical framework, which explicitly includes all leading order processes involving light flavor degrees of freedom, we investigate the thermalization process of homogeneous and isotropic plasmas far-from equilibrium and determine the relevant timescales for kinetic and chemical equilibration. We further simulate the longitudinally expanding preequilibrium plasma created in ultrarelativistic heavy-ion collisions at zero and nonzero density of the conserved charges and study its microscopic and macroscopic evolution toward equilibrium.

We study how to unravel the dark matter blind spots by phase transition gravitational waves in synergy with collider signatures at electroweak one-loop level taking the inert doublet model as an example. We perform a detailed Monte Carlo study at the future lepton colliders in the favored parameter space, which is consistent with current dark matter experiments and collider constraints. Our studies demonstrate that the Circular Electron Positron Collider and other future lepton colliders have the potential to explore the dark matter blind spots.

In this work, we study gravity duals of conformal field theories with boundaries—known as AdS/BCFT correspondence, put forward by Takayanagi [Phys. Rev. Lett. 107, 101602 (2011)]—within a scalar-tensor theory, as proposed by Horndeski in 4D [Int. J. Theor. Phys. 10, 363 (1974)]. We consider the case of 3D gravity dual to 2D BCFT, take a Gibbons-Hawking surface term modified by Horndeski’s theory, and find the corresponding 3D (Bañados-Teitelboim-Zanelli) black hole solutions. We analyze the effects of Horndeski gravity on the profile of the extra boundary for the black hole by using an approximate analytic solution. Performing a holographic renormalization, we calculate the free energy and obtain the total entropy and corresponding area, as well as the boundary entropy for the black hole. In particular, the boundary entropy found here can be seen as an extension of the one proposed by Takayanagi. From the free energy, we perform a systematic study of the 3D black hole thermodynamics and present, among our results, an indication of the restoration of conformal symmetry for high temperatures. Finally, we present a study on the influence of Horndeski gravity on the Hawking-Page phase transition where we can see the stable and unstable phases throughout the plane of free energy versus temperature.

In local scalar quantum field theories at finite temperature correlation functions are known to satisfy certain nonperturbative constraints, which for two-point functions in particular implies the existence of a generalization of the standard Källén-Lehmann representation. In this work, we use these constraints in order to derive a spectral representation for the shear viscosity arising from the thermal asymptotic states, ${\eta }_0$. As an example, we calculate ${\eta }_0$ in ${\varphi }^4$ theory, establishing its leading behavior in the small and large coupling regimes.

Using gravitational wave observations to search for deviations from general relativity (GR) in the strong-gravity regime has become an important research direction. One aspect of the strong gravity modifications to GR is parity violation. Chern Simons (CS) gravity is one of the most frequently studied parity-violating models of strong gravity. CS gravity is indistinguishable from GR for all conformally flat space-times and for space-times that possess a maximally symmetric two-dimensional subspace. Also, it is known that the Kerr black hole is not a solution for CS gravity. At the same time, the only rotating solution available in the literature for dynamical CS (DCS) gravity is the slow-rotating case most accurately known to quadratic order in spin. In this work, for the slow-rotating case (accurate to first order in spin), we derive the linear perturbation equations governing the metric and the DCS field accurate to linear order in spin and quadratic order in the CS coupling parameter ($\alpha$) and obtain the quasinormal mode (QNM) frequencies. After confirming the recent results of Wagle et al. arXiv:2103.09913, we find an additional contribution to the eigenfrequency correction at the leading perturbative order of ${\alpha }^2$. Unlike Wagle et al., we also find corrections to frequencies in the polar sector. We compute these extra corrections by evaluating the expectation values of the perturbative potential on unperturbed QNM wave functions along a contour deformed into the complex-$r$ plane. For $\alpha =0.1M^2$, we obtain the ratio of the imaginary parts of the DCS correction to the GR correction in the first QNM frequency (in the polar sector) to be 0.263 implying significant change. For the (2, 2) mode, the DCS corrections make imaginary part of the first QNM of the fundamental mode less negative, thereby decreasing the decay rate. Our results, along with future gravitational wave observations, can be used as a test for DCS gravity and to further constrain the CS coupling parameters.

We study the dynamical Chern-Simons gravity as an effective quantum field theory, and discuss a broad range of its parameter space where the theory is valid. Within that validity range, we show that slowly rotating black holes acquire novel geometric structures due to the gravitational dynamical Chern-Simons term. In particular, the rotating black-hole solutions get endowed with two caplike domains, emanating from the north and south poles in the standard Boyer-Lindquist coordinates. The domains extend out to a distance that is approximately a few percent of the black hole’s size. The caplike domains have an unusual equation of state, pointing to nonstandard dynamics within the caps. In particular, the focusing condition for geodesics is violated in those domains. This in turn implies that the Hawking-Penrose singularity theorem cannot be straightforwardly applied to hypothetical probe matter placed within the Chern-Simons caps.

We obtain a remarkable semianalytic expression concerning the role of purely tidal curvature on accelerated probes, revealing some novel insights into the role of absolute vs tidal acceleration in the response of such probes. The key quantity we evaluate is the relation between geodesic (${\tau }_{\mathrm{geod}}$) and proper time (${\tau }_{\mathrm{acc}}$) intervals between events on the probe trajectory. This is obtained as a covariant power series in curvature using a combination of analytical and numerical tools. A serendipitous observation then reveals that one can exactly sum all terms involving the purely tidal component ${ℰ}_n=R_{abcd}{ϵ}^{ab}{ϵ}^{cd}$ of curvature, with ${ϵ}^{ab}$ the binormal to the plane of motion, ${\tau }_{\mathrm{geod}}=\frac{2}{\sqrt{{-ℰ}_n}}{\sinh }^{-1}[\sqrt{\frac{-{ℰ}_n}{a^2-{ℰ}_n}}\sinh (\frac{1}{2}\sqrt{a^2-{ℰ}_n}{\tau }_{\mathrm{acc}})]$. For classical clocks, the above result represents an interesting closed form contribution of tidal curvature to the differential ageing of twins in the classic twin paradox. For quantum probes, it gives a thermal contribution to the detector response with a modified Unruh temperature, $[k_{\mathrm{B}}T{]}_{{ℰ}_n}=\frac{\hslash \sqrt{a^2-{ℰ}_n}}{2\pi }$. As an operational tool, the computational framework we present and the corresponding results should find applications to a wide range of physical problems that involve measurements and observations by use of accelerated probes in curved spacetimes.

A powerful technique to calculate gravitational radiation from binary systems involves a perturbative expansion: if the masses of the two bodies are very different, the “small” body is treated as a point particle of mass $m_p$ moving in the gravitational field generated by the large mass $M$, and one keeps only linear terms in the small mass ratio $m_p/M$. This technique usually yields finite answers, which are often in good agreement with fully nonlinear numerical relativity results, even when extrapolated to nearly comparable mass ratios. Here we study two situations in which the point-particle approximation yields a divergent result: the instantaneous flux emitted by a small body as it orbits the light ring of a black hole, and the total energy absorbed by the horizon when a small body plunges into a black hole. By integrating the Teukolsky (or Zerilli/Regge-Wheeler) equations in the frequency and time domains we show that both of these quantities diverge. We find that these divergences are an artifact of the point-particle idealization, and are able to interpret and regularize this behavior by introducing a finite size for the point particle. These divergences do not play a role in black-hole imaging, e.g., by the Event Horizon Telescope.

We perform a comprehensive study of cosmological constraints on nonstandard neutrino self-interactions using cosmic microwave background and baryon acoustic oscillation data. We consider different scenarios for neutrino self-interactions distinguished by the fraction of neutrino states allowed to participate in self-interactions and how the relativistic energy density, $N_{\mathrm{eff}}$, is allowed to vary. Specifically, we study cases in which all neutrino states self-interact and $N_{\mathrm{eff}}$ varies; two species free-stream, which we show alleviates tension with laboratory constraints, while the energy in the additional interacting states varies; and a variable fraction of neutrinos self-interact with either the total $N_{\mathrm{eff}}$ fixed to the Standard Model value or allowed to vary. In no case do we find compelling evidence for new neutrino interactions or nonstandard values of $N_{\mathrm{eff}}$. In several cases, we find additional modes with neutrino decoupling occurring at lower redshifts $z_{\mathrm{dec}}\sim {10}^{3–4}$. We do a careful analysis to examine whether new neutrino self-interactions solve or alleviate the so-called $H_0$ tension and find that, when all Planck 2018 CMB temperature and polarization data are included, none of these examples eases the tension more than allowing a variable $N_{\mathrm{eff}}$ comprised of free-streaming particles. Although we focus on neutrino interactions, these constraints are applicable to any light relic particle.

The dark matter (DM) can consist of the primordial black holes (PBHs) in addition to the conventional weakly interacting massive particles (WIMPs). The Poisson fluctuations of the PBH number density produce the isocurvature perturbations which can dominate the matter power spectrum at small scales and enhance the early structure formation. We study how the WIMP annihilation from those early formed structures can affect the cosmic microwave background (in particular the $E$-mode polarization anisotropies and $y$-type spectral distortions) and global 21-cm signals. Our studies would be of particular interest for the light (sub-GeV) WIMP scenarios which have been less explored compared with the mixed DM scenarios consisting of PBHs and heavy ($\gtrsim 1\mathrm{GeV}$) WIMPs. For instance, for the self-annihilating DM mass $m_{\chi }=1\mathrm{MeV}$ and the thermally averaged annihilation cross section $⟨\sigma v⟩\sim {10}^{-30}{\mathrm{cm}}^3/\mathrm{s}$, the latest Planck cosmic microwave background data requires the PBH fraction with respect to the whole DM to be at most $\mathcal{O}({10}^{-3})$ for the subsolar mass PBHs and an even tighter bound (by a factor $\sim 5$) can be obtained from the global 21-cm measurements.

We provide a first systematic and quantitative discussion of the phenomenology of the nonrelativistic effective Hamiltonian describing the nuclear scattering process for a weakly interacting massive particle (WIMP) of arbitrary spin $j_{\chi }$. To this aim we obtain constraints from a representative sample of present direct detection experiments assuming the WIMP-nucleus scattering process to be driven by each one of the 44 effective couplings that arise for $j_{\chi }\le 2$. We find that a high value of the multipolarity $s\le 2j_{\chi }$ of the coupling, related to the power of the momentum transfer $q$ appearing in the scattering amplitude, leads to a suppression of the expected rates and pushes the expected differential spectra to large recoil energies $E_R$. For $s\le 4$ the effective scales probed by direct detection experiments can be suppressed by up to five orders of magnitude compared to the case of a standard spin-independent interaction. For operators with large $s$ the expected differential spectra can be pushed to recoil energies in the MeV range, with the largest part of the signal concentrated at $E_R\gtrsim 100\mathrm{keV}$ and a peculiar structure of peaks and minima arising when both the nuclear target and the WIMPs are heavy. As a consequence the present bounds on the effective operators can be significantly improved by extending the recoil energy intervals to higher recoil energies. Our analysis assumes effective interaction operators that are irreducible under the rotation group. Such operators drive the interactions of high-multipole dark matter candidates, i.e., states that possess only the highest multipole allowed by their spin. As a consequence our analysis represents also the first phenomenological study of the direct detection of quadrupolar, octupolar, and hexadecapolar dark matter.

We introduce a systematic approach to characterize the most general nonrelativistic weakly interacting massive particle (WIMP)-nucleus interaction allowed by Galilean invariance for a WIMP of arbitrary spin $j_{\chi }$ in the approximation of one-nucleon currents and for a WIMP-nucleon effective potential at most linear in the velocity. Under these assumptions our framework can be matched to any high-energy model of particle dark matter, including elementary particles and composite states. Five nucleon currents arise from the nonrelativistic limit of the free nucleon Dirac bilinears. Our procedure consists in (1) organizing the WIMP currents according to the rank of the $2j_{\chi }+1$ irreducible operator products of up to $2j_{\chi }$ WIMP spin vectors, and (2) coupling each of the WIMP currents to each of the five nucleon currents. The transferred momentum $q$ appears to a power fixed by rotational invariance. For a WIMP of spin $j_{\chi }$ we find a basis of $4+20j_{\chi }$ independent operators that exhaust all the possible operators that drive elastic WIMP-nucleus scattering in the approximation of one-nucleon currents. By comparing our operator basis, which is complete, to the operators already introduced in the literature we show that some of the latter for $j_{\chi }=1$ were not independent and some were missing. We provide explicit formulas for the squared scattering amplitudes in terms of the nuclear response functions, which are available in the literature for most of the targets used in WIMP direct detection experiments.

Gravitational wave interferometers achieve their profound sensitivity by combining a Michelson interferometer with optical cavities, suspended masses, and now, squeezed quantum states of light. These states modify the measurement process of the LIGO, VIRGO and GEO600 interferometers to reduce the quantum noise that masks astrophysical signals; thus, improvements to squeezing are essential to further expand our gravitational view of the Universe. Further reducing quantum noise will require both lowering decoherence from losses as well more sophisticated manipulations to counter the quantum back-action from radiation pressure. Both tasks require fully understanding the physical interactions between squeezed light and the many components of km-scale interferometers. To this end, data from both LIGO observatories in observing run three are expressed using frequency-dependent metrics to analyze each detector’s quantum response to squeezed states. The response metrics are derived and used to concisely describe physical mechanisms behind squeezing’s simultaneous interaction with transverse-mode selective optical cavities and the quantum radiation pressure noise of suspended mirrors. These metrics and related analysis are broadly applicable for cavity-enhanced optomechanics experiments that incorporate external squeezing, and—for the first time—give physical descriptions of every feature so far observed in the quantum noise of the LIGO detectors.

We develop a numerical method to nonperturbatively study scattering and gluon emission of a quark from a colored target using a light-front Hamiltonian approach. The target is described as a classical color field, as in the color glass condensate effective theory. The Fock space of the scattering system is restricted to the $|q⟩+|qg⟩$ sectors, but the time evolution of this truncated system is solved exactly. This method allows us to study the interplay between coherence and multiple scattering in gluon emission. It could be applied both to studying subeikonal effects in high-energy scattering and to understanding jet quenching in a hot plasma.