We show how a suitably prepared set of clocks can be used to determine all components of the gravitational field in general relativity. We call such an experimental setup a clock compass, in analogy to the usual gravitational compass. Particular attention is paid to the construction of the underlying reference frame. Conceptual differences between the clock compass and the standard gravitational compass, which is based on the measurement of the mutual accelerations between the constituents of a swarm of test bodies, are highlighted. Our results are of direct operational relevance for the setup of networks of clocks, for example in the context of relativistic geodesy.

We investigate the stability analysis of a Schwarzschild black hole in Einstein-scalar-Gauss-Bonnet theory because the instability of the Schwarzschild black hole without scalar hair implies the Gauss-Bonnet black hole with scalar hair. The linearized scalar equation is compared to the Lichnerowicz-Ricci tensor equation in the Einstein-Weyl gravity. It turns out that the instability of the Schwarzschild black hole in Einstein-scalar-Gauss-Bonnet theory is interpreted as not the tachyonic instability but the Gregory-Laflamme instability of a black string. In the small mass regime of $1/\lambda <1.174/r_{+}$, the Schwarzschild solution becomes unstable, and a new branch of the solution with scalar hair bifurcates from the Schwarzschild one. This is very similar to finding a newly non-Schwarzschild black hole in Einstein-Weyl gravity.

Gravitational waves detected by advanced ground-based detectors have allowed studying the Universe in a way which is fully complementary to electromagnetic observations. As more sources are detected, it will be possible to measure properties of the local population of black holes and neutron stars, including their mass and spin distributions. Once at design sensitivity, existing instruments will be able to detect heavy binary black holes at redshifts of $\sim 1$. Significant upgrades in the current facilities could increase the sensitivity by another factor of few, further extending reach and signal-to-noise ratio. More is required to access the most remote corners of the Universe. Third-generation gravitational-wave detectors have been proposed, which could observe most of the binary black holes merging anywhere in the Universe. In this paper, we check if, and to which extent, it makes sense to keep previous-generation detectors up and running once a significantly more sensitive detector is online. First, we focus on a population of binary black holes with redshifts distributed uniformly in comoving volume. We show that measurement of extrinsic parameters, such as sky position, inclination and luminosity distance can significantly benefit from the presence of a less sensitive detector. Conversely, intrinsic parameters such as detector-frame masses and spins are largely unaffected. Measurement of the source-frame masses is instead improved, owing to the improvement of the distance measurement. Then, we focus on nearby events. We simulated sources similar to GW150914 and GW151226 and check how well their parameters can be measured by various networks. Here, too, we find that the main difference is a better estimation of the sky position, although even a single triangular-shaped third-generation detector can estimate their sky position to $1{\mathrm{deg}}^2$ or better.

Transient gravitational-wave searches can be divided into two main families of approaches: modeled and unmodeled searches, based on matched filtering techniques and time-frequency excess power identification respectively. The former, mostly applied in the context of compact binary searches, relies on the precise knowledge of the expected gravitational-wave phase evolution. This information is not always available at the required accuracy for all plausible astrophysical scenarios, e.g., in the presence of orbital precession, or eccentricity. The other search approach imposes little priors on the targeted signal. We propose an intermediate route based on a modification of unmodeled search methods in which time-frequency pattern matching is constrained by astrophysical waveform models (but not requiring accurate prediction for the waveform phase evolution). The set of astrophysically motivated patterns is conveniently encapsulated in a graph, that encodes the time-frequency pixels and their co-occurrence. This allows the use of efficient graph-based optimization techniques to perform the pattern search in the data. We show in the example of black-hole binary searches that such an approach leads to an averaged increase in the distance reach ($+7–8\%$) for this specific source over standard unmodeled searches.

We consider the static domain wall braneworld scenario constructed from the Palatini formalism $f(\mathcal{R})$ theory. We check the self-consistency under scalar perturbations. By using the scalar-tensor formalism we avoid dealing with the higher-order equations. We develop the techniques to deal with the coupled system. We show that under some conditions, the scalar perturbation simply oscillates with time, which guarantees the stability. We also discuss the localization condition of the scalar mode by analyzing the effective potential and the fifth-dimensional profile of the scalar mode. We apply these results to an explicit example, and show that only some of the solutions allow for stable scalar perturbations. These stable solutions also give nonlocalizable massless mode. This is important for reproducing a viable four-dimensional gravity.

We study statistical anisotropies generated in the observed two-point function of the cosmic microwave background (CMB) fluctuations if the primordial statistics are non-Gaussian. Focusing on the dipole modulations of the anisotropies, we find that the hemispherical power asymmetry observed in the CMB temperature fluctuations can be modeled by a local-type trispectrum with amplitude ${\tau }_{\mathrm{NL}}(k_p=0.05{\mathrm{Mpc}}^{-1})\approx 2\times {10}^4$ and a large red tilt $n\approx -0.68$. We numerically evaluate the non-Gaussian covariance of the modulation estimators for both temperature and E-mode polarization fluctuations and discuss the prospects of constraining the model using Planck satellite data. We then discuss other effects of the scale-dependent trispectrum that could be used to distinguish this scenario from other explanations of the power asymmetry: higher-order modulations of the two-point function and the non-Gaussian angular power spectrum covariance. As an important consequence of the non-Gaussian power spectrum covariance, we discuss how the CMB-inferred spectral index of primordial scalar fluctuations can be significantly biased in the presence of a scale-dependent local-type trispectrum.

Gravitons are the quantum counterparts of gravitational waves in low-energy theories of gravity. Using Feynman rules one can compute scattering amplitudes describing the interaction between gravitons and other fields. Here, we consider the interaction between gravitons and photons. Using the quantum Boltzmann equation formalism, we derive fully general equations describing the radiation transfer of photon polarization, due to the forward scattering with gravitons. We show that the Q and U photon linear polarization modes couple with the V photon circular polarization mode, if gravitons have anisotropies in their power-spectrum statistics. As an example, we apply our results to the case of primordial gravitons, considering models of inflation where an anisotropic primordial graviton distribution is produced. Finally, we evaluate the effect on cosmic microwave background (CMB) polarization, showing that in general the expected effects on the observable CMB frequencies are very small. However, our result is promising, since it could provide a novel tool for detecting anisotropic backgrounds of gravitational waves, as well as for getting further insight on the physics of gravitational waves.

High precision astrometry now enables us to measure the time drift of astrophysical observables in real time, hence providing new ways to probe different cosmological models. This article presents a general derivation of the redshift and direction drifts for general observers. It is then applied to the standard cosmological framework of a Friedmann-Lemaître spacetime including all effects at first order in the cosmological perturbations, as well as in the class of spatially anisotropic universe models of the Bianchi I family. It shows that for a general observer, the direction drift splits into a parallax and an aberration drifts and order of magnitude estimates of these two components are provided. The multipolar decomposition of the redshift and aberration drifts is also derived and shows that the observer’s peculiar velocity contributes only as a dipole whereas the anisotropic shear contributes as a quadrupole.

In this paper we place observational constraints on the well-known $\gamma$-gravity $f(R)$ model using the latest cosmological data, namely we use the latest growth rate, Cosmic Microwave Background, Baryon Acoustic Oscillations, Supernovae type Ia and Hubble parameter data. Performing a joint likelihood analysis we find that the $\gamma$-gravity model is in very good agreement with observations. Utilizing the AIC statistical test we statistically compare the current $f(R)$ model with $\mathrm{\Lambda }\mathrm{CDM}$ cosmology and find that they are statistically equivalent. Therefore, $\gamma$-gravity can be seen as a useful scenario toward testing deviations from General Relativity. Finally, we note that we find somewhat higher values for the $f(R)$ best-fit values compared to those mentioned in the past in the literature and we argue that this could potential alleviate the halo-mass function problem.

If the inflaton couples to other degrees of freedom (d.o.f.) that populate the postinflationary stage, such coupling modifies the dynamics of the inflaton during inflation. We consider light fermions Yukawa coupled to the inflaton as “unobserved” d.o.f. integrated out of the total density matrix. Tracing out these d.o.f. yields a mixed density matrix whose time evolution is described by an effective field theory. We show that the coupling leads to profuse fermion pair production for super-Hubble inflaton fluctuations which lead to the growth of entanglement entropy during inflation. The power spectrum of inflaton fluctuations features scale invariance violations $\mathcal{P}(k)={\mathcal{P}}_0(k)\exp \{8{\xi }_k\}$ with corrections to the index and its running directly correlated with the entanglement entropy: $S_{vN}=-\sum _k[\ln (1-{\xi }_k)+\frac{{\xi }_k\ln ({\xi }_k)}{1-{\xi }_k}]$. For super-Hubble fluctuations we find ${\xi }_k=-\frac{Y^2}{48{\pi }^2}\{2N_T\ln (k/k_f)+{\ln }^2(k/k_f)\}$ with $Y$ the Yukawa coupling, $N_T$ the total number of e-folds during inflation, and $k_f$ a “pivot” scale corresponding to the mode that crosses the Hubble radius at the end of inflation.

The Sydney University Giant Air-shower Recorder (SUGAR) measured the energy spectrum of ultra-high-energy cosmic rays reconstructed from muon-detector readings, while the Pierre Auger Observatory, looking at the same Southern sky, used the calorimetric fluorescence method for the same purpose. Comparison of their two spectra allows us to reconstruct the empirical dependence of the number of muons in a vertical shower on the primary energy for energies between $10^{17}$ and $10^{18.5}\mathrm{eV}$. We compare this dependence with the predictions of hadronic interaction models QGSJET-II-04, EPOS-LHC and SIBYLL-2.3c. The empirically determined number of muons with energies above 0.75 GeV in a vertical shower exceeds the simulated one by the factors $\sim 1.7$ and $\sim 1.3$ for $10^{17}\mathrm{eV}$ proton and iron primaries, respectively. The muon excess grows moderately with the primary energy, increasing by an additional factor of $\sim 1.2$ for $10^{18.5}\mathrm{eV}$ primaries.

We prove that all connected $n$-point Green functions of four-dimensional topological Yang-Mills theories quantized in the (anti-)self-dual Landau gauges are tree-level exact, i.e., there are no radiative corrections in this gauge choice.

We systematically study quantum effect on chiral and $U_A(1)$ symmetry breaking under external electromagnetic fields in the frame of equal-time Wigner function formalism. We derive the transport and constraint equations for the quark distribution functions and the chiral and pion condensates in a Nambu–Jona-Lasinio model. By taking semiclassical expansion of the equations, chiral symmetry is broken at classical level, while $U_A(1)$ symmetry breaking happens only at quantum level. Beyond quasiparticle approximation, the quark off-shell effect leads to strong oscillation for the chiral and pion condensates.

Quantum mechanical interactions between neutrinos and matter along the path of propagation, the Wolfenstein matter effect, are of particular importance for the upcoming long-baseline neutrino oscillation experiments, specifically the Deep Underground Neutrino Experiment (DUNE). Here, we explore specifically what about the matter density profile can be measured by DUNE, considering both the shape and normalization of the profile between the neutrinos’ origin and detection. Additionally, we explore the capability of a perturbative method for calculating neutrino oscillation probabilities and whether this method is suitable for DUNE. We also briefly quantitatively explore the ability of DUNE to measure the Earth’s matter density, and the impact of performing this measurement on measuring standard neutrino oscillation parameters.

We investigate the production and decays of doubly-charged Higgs bosons for the Type-II seesaw mechanism at an $e^{+}{e}^{-}$ collider with two center of mass energies, $\sqrt{s}=380\mathrm{GeV}$ and 3 TeV, and analyze the fully hadronic final states in detail. Lower mass ranges can be probed during the 380 GeV run of the collider, while high mass ranges, which are beyond the 13 TeV Large Hadron Collider discovery reach, can be probed with $\sqrt{s}=3\mathrm{TeV}$. For such a heavy Higgs boson, the final decay products are collimated, resulting in fat-jets. We perform a substructure analysis to reduce the background and find that a doubly-charged Higgs boson in the mass range 800–1120 GeV can be discovered during the 3 TeV run, with integrated luminosity $\mathcal{L}\sim 95{\mathrm{fb}}^{-1}$ of data. For 380 GeV center of mass energy, we find that for the doubly-charged Higgs boson in the range 160–172 GeV, a $5\sigma$ significance can be achieved with only integrated luminosity $\mathcal{L}\sim 24{\mathrm{fb}}^{-1}$. Therefore, a light Higgs boson can be discovered immediately during the run of a future $e^{+}{e}^{-}$ collider.

We study the off-shell production of the Higgs boson at the LHC to probe Higgs physics at higher energy scales utilizing the process $gg\to h^{*}\to ZZ$. We focus on the energy scale dependence of the off-shell Higgs propagation, and of the top quark Yukawa coupling, $y_t(Q^2)$. Extending our recent study [D. Goncalves, T. Han, and S. Mukhopadhyay, Phys. Rev. Lett. 120, 111801 (2018).], we first discuss threshold effects in the Higgs propagator due to the existence of new states, such as a gauge singlet scalar portal, and a possible continuum of states in a conformal limit, both of which would be difficult to discover in other traditional searches. We then examine the modification of $y_t(Q^2)$ from its Standard Model (SM) prediction in terms of the renormalization group running of the top Yukawa, which could be significant in the presence of large flat extra dimensions. Finally, we explore possible strongly coupled new physics in the top-Higgs sector that can lead to the appearance of a nonlocal $Q^2$-dependent form factor in the effective top-Higgs vertex. We find that considerable deviations compared to the SM prediction in the invariant mass distribution of the $Z$-boson pair can be conceivable, and may be probed at the $2\sigma$ level at the high-luminosity 14 TeV HL-LHC for a new physics scale up to $\mathcal{O}(1\mathrm{TeV})$, and at the upgraded 27 TeV HE-LHC for a scale up to $\mathcal{O}(3\mathrm{TeV})$. For a few favorable scenarios, $5\sigma$ level observation may be possible at the HE-LHC for a scale of about $\mathcal{O}(1\mathrm{TeV})$.

We propose a new model of five-dimensional $SU(3)\otimes U(1{)}_X$ gauge-Higgs unification with a successful electroweak symmetry breaking and a realistic Higgs boson mass. In our model, the representations of the fermions are very simple, the $\mathbf{3},\overline{\mathbf{3}}$ and $\overline{\mathbf{15}}$ representations of $SU(3)$ gauge group. Employing the antiperiodic boundary conditions for $\overline{\mathbf{15}}$ reduces massless exotic fermions and simplifies the brane-localized mass terms. We calculate the one-loop Higgs potential in detail and find that a realistic electroweak symmetry breaking and the observed Higgs mass are obtained.

When building $CP$-symmetric models beyond the Standard Model, one can impose $CP$ symmetry of higher order. This means that one needs to apply the $CP$ transformation more than two times to get the identity transformation, but still the model is perfectly $CP$-conserving. A multi-Higgs-doublet model based on $CP$ symmetry of order 4, dubbed CP4, was recently proposed and its phenomenology is being explored. Here, we show that the construction does not stop at CP4. We build examples of renormalizable multi-Higgs-doublet potentials which are symmetric under CP8 or CP16, without leading to any accidental symmetry. If the vacuum conserves $CP$ symmetry of order $2k$, then the neutral scalars become $CP$ eigenstates, which are characterized not by $CP$ parities but by $CP$ charges defined modulo $2k$. One or more lightest states can be the dark matter candidates, which are protected against decay not by the internal symmetry but by the exotic $CP$. We briefly discuss their mass spectra and interaction patterns for CP8 and CP16.

We consider the extension of the Standard Model with a light inflaton where both the unitarity problem in Higgs inflation and the vacuum instability problem are resolved. The linear nonminimal coupling of the inflaton to gravity leads to a significant kinetic mixing between the inflaton and the graviton such that perturbative unitarity is restored up to the Planck scale. We show the correlation between the unitarity scale and inflationary observables in this model and discuss how the effective Higgs inflation appears.

We formulate the quantum field theory description of neutron-antineutron oscillations in the framework of canonical quantization, in analogy with the Bardeen–Cooper–Schrieffer theory and the Nambu–Jona-Lasinio model. The physical vacuum of the theory is a condensate of pairs of would-be neutrons and antineutrons in the absence of the baryon-number violating interaction. The quantization procedure defines uniquely the mixing of massive Bogoliubov quasiparticle states that represent the neutron. In spite of not being mass eigenstates, neutron and antineutron states are defined on the physical vacuum and the oscillation formulated in asymptotic states. The exchange of the baryonic number with the vacuum condensate engenders what may be observed as neutron-antineutron oscillation. The convergence between the present canonical approach and the Lagrangian/path integral approach to neutron oscillations is shown by the calculation of the anomalous (baryon-number violating) propagators. The quantization procedure proposed here can be extended to neutrino oscillations and, in general, to any particle oscillations.