We show that large gauge transformations in asymptotically flat spacetime can be implemented by sandwiching a shell containing the ingoing hard particles between two finite-width shells of soft gauge excitations. Integration of the graviton Dirac bracket implies that our observable soft degrees of freedom obey the algebra imposed by Strominger et al. on unobservable boundary degrees of freedom. Thus, we provide both a derivation and an observable realization of this algebra. We recently showed that soft charges fail to constrain the hard scattering problem, and so cannot be relevant to the black hole information paradox. By expressing the Bondi–van der Burg–Metzner–Sachs (BMS) algebra in terms of observable quantities, the present work shows that this conclusion was not an artifact of working with strictly zero frequency soft modes. The conservation laws associated with asymptotic symmetries are seen to arise physically from free propagation of infrared modes.

Resorting to Wilsonian renormalization group (RG) transformations, we propose an emergent geometric description for a topological phase transition in the Kitaev superconductor model. An effective field theory consists of an emergent bulk action with an extra dimension, an ultraviolet (UV) boundary condition for an initial value of a coupling function, and an infrared (IR) effective action with a fully renormalized coupling function. The bulk action describes the evolution of the coupling function along the direction of the extra dimension, where the extra dimension is identified with an RG scale and the resulting equation of motion is nothing but a $\beta$ function. In particular, the IR effective field theory turns out to be consistent with a Callan-Symanzik equation which takes into account both the bulk and IR boundary contributions. This derived Callan-Symanzik equation gives rise to a metric structure. Based on this emergent metric tensor, we uncover the equivalence of the entanglement entropy between the emergent geometric description and the quantum field theory in the vicinity of the quantum critical point.

We examine the effect of a wiggly cosmic string for both massless and massive particle propagation along the string axis. We show that the wave equation that governs the propagation of a scalar field in the neighborhood of a wiggly string is formally equivalent to the quantum wave equation describing the hydrogen atom in two dimensions. We further show that the wiggly string spacetime behaves as a gravitational waveguide in which the quantized wave modes propagate with frequencies that depend on the mass, string energy density, and string tension. We propose an analogy with an optical fiber, defining an effective refractive index likely to mimic the cosmic string effect in the laboratory.

The gravitational wave source localization problem is important in gravitational wave astronomy. About the source localization problem of ground-based detectors, almost all of the previous investigations only considered the arrival time difference. Within the matched filtering framework, the information beside the arrival time difference can possibly also help with source localization. Especially when an eccentric binary is considered, the character involved in the gravitational waveform may improve the source localization. We investigate this effect systematically in the current paper. During the investigation, the enhanced postcircular waveform model is used to describe the eccentric binary coalesce. We find that the source localization accuracy does increase along with the eccentricity increases. But such improvement depends on the total mass of the binary. For total mass $100M_{\odot }$ binary, the source localization accuracy may be improved about two times in general when the eccentricity increases from 0 to 0.4. For a total mass $65M_{\odot }$ binary (GW150914-like binary), the improvement factor is about 1.3 when the eccentricity increases from 0 to 0.4. For a total mass $22M_{\odot }$ binary (GW151226-like binary), such improvement is ignorable.

We present a comprehensive comparison of the spin-aligned effective-one-body (EOB) waveform model of Nagar et al. [Phys. Rev. D 93, 044046 (2016)], informed using 39 numerical-relativity (NR) data sets, against a set of 149 $\ell =m=2$ NR waveforms freely available through the Simulating Extreme Spacetimes (SXS) catalog. We find that, without further calibration, these EOBNR waveforms have unfaithfulness—at design Advanced-LIGO sensitivity and evaluated with total mass $M$ varying as $10M_{\odot }\le M\le 200M_{\odot }$—always below 1% against all NR waveforms except for three outliers, that still never exceed the 3% level; with a minimal retuning of the (effective) next-to-next-to-next-to-leading-order spin-orbit coupling parameter for the non-equal-mass and non-equal-spin sector, that only needs three more NR waveforms, one is left with another two (though different) outliers, with maximal unfaithfulness of up to only 2% for a total mass of $200M_{\odot }$. We show this is the effect of slight inaccuracies in the phenomenological description of the postmerger waveform of Del Pozzo and Nagar [Phys. Rev. D 95, 124034 (2017)] that was constructed by interpolating over only 40 NR simulations. We argue that this can be easily fixed by using either an alternative ringdown description (e.g., the superposition of quasi-normal-modes) or an improved version of the phenomenological representation. By analyzing a NR waveform with a mass ratio 8 and dimensionless spins $+0.85$ obtained with the bam code, we conclude that the model would benefit from NR simulations specifically targeted at improving the postmerger-ringdown phenomenological fits for mass ratios $\gtrsim 8$ and spins $\gtrsim 0.8$. We finally show that some of the longest SXS $q=7$ waveforms suffer from systematic uncertainties in the postmerger-ringdown part that are interpreted as due to unphysical drifts of the center of mass: thus some care should be applied when these waveforms are used for informing analytical models.

We investigate the scattering of a spinning test particle by a Kerr black hole within the Mathisson-Papapetrou-Dixon model to linear order in spin. The particle’s spin and orbital angular momentum are taken to be aligned with the black hole’s spin. Both the particle’s mass and spin length are assumed to be small in comparison with the characteristic length scale of the background curvature, in order to avoid backreaction effects. We analytically compute the modifications due to the particle’s spin to the scattering angle, the periastron shift, and the condition for capture by the black hole, extending previous results valid for the nonrotating Schwarzschild background. Finally, we discuss how to generalize the present analysis beyond the linear approximation in spin, including spin-squared corrections in the case of a black-hole-like quadrupolar structure for the extended test body.

We present predictions of the Kähler moduli inflation model for the spectral tilt by parametrizing the reheating epoch by an effective equation-of-state parameter and the number of e-foldings of reheating; and taking into account the post-inflationary history of the model. This model has an epoch in which the energy density of the universe is dominated by cold moduli particles. We compare our results with data from the Planck mission and find that exotic reheating (with effective equation of state $w_{\mathrm{re}}$ greater than $1/3$) or dark radiation is required to match the observations. For canonical reheating case with $w_{\mathrm{re}}=0$, we deduce ${\log }_{10}(T_{\mathrm{re}}/{10}^3\mathrm{GeV})\simeq 1190(n_s-0.956)$. We also analyze our results in the context of observations being planned for the future and their projected sensitivities.

We study the dynamics of a hierarchical three-body system in the general relativistic regime: an extreme mass-ratio inner binary under the tidal influence of an external body. The inner binary consists of a central Schwarzschild black hole and a test body moving around it. We discuss three types of tidal effects on the orbit of the test body. First, the angular momentum of the inner binary precesses around the angular momentum of the outer binary. Second, the tidal field drives a “transient resonance” when the radial and azimuthal frequencies are commensurable. In contrast with resonances driven by the gravitational self-force, this tidal-driven resonance may boost the orbital angular momentum and eccentricity (a relativistic version of the Kozai-Lidov effect). Finally, for an orbit-dynamical effect during the nonresonant phase, we calculate the correction to the innermost stable circular (mean) orbit due to the tidal interaction. Hierarchical three-body systems are potential sources for future space-based gravitational wave missions, and the tidal effects that we find could contribute significantly to their waveform.

Assuming the existence of a local, analytic, unitary UV completion in a Poincaré invariant scalar field theory with a mass gap, we derive an infinite number of positivity requirements using the known properties of the amplitude at and away from the forward scattering limit. These take the form of bounds on combinations of the pole subtracted scattering amplitude and its derivatives. In turn, these positivity requirements act as constraints on the operator coefficients in the low energy effective theory. For certain theories these constraints can be used to place an upper bound on the mass of the next lightest state that must lie beyond the low energy effective theory if such a UV completion is to ever exist.

Due to integrability, baryon-baryon scattering in the massless Gross-Neveu model at large $N$ features only forward elastic scattering. A bare mass term breaks integrability and is therefore expected to induce backward elastic scattering as well as inelastic reactions. We confirm these expectations by a study of baryon-baryon scattering in the massive Gross-Neveu model near the nonrelativistic limit. This restriction enables us to solve the time-dependent Hartree-Fock equations with controlled approximations, using a combination of analytical methods from an effective field theory and the numerical solution of partial differential equations.

LHC experiments can provide a remarkable sensitivity to exotic metastable massive particles, decaying with significant displacement from the interaction point. The best sensitivity is achieved with models where the production and decay occur due to different coupling constants, and the lifetime of exotic particles determines the probability of decay within a detector. The lifetimes of such particles can be independently limited from standard cosmology, in particular, the big bang nucleosynthesis (BBN). In this paper, we analyze the constraints on the simplest scalar model coupled through the Higgs portal, where the production occurs via $h\to SS$, and the decay is induced by the small mixing angle of the Higgs field $h$ and scalar $S$. We find that throughout most of the parameter space, $2m_{\mu }<m_S<m_h/2$, the lifetime of an exotic particle has to be less than 0.1 s, while below $2m_{\mu }$ it could grow to about a second. The strong constraints on lifetimes are induced by the nucleonic and mesonic decays of scalars that tend to raise the $n/p$ ratio. Strong constraints on lifetimes of the minimal singlet extensions of the Higgs potential are welcome news for the MATHUSLA proposal that seeks to detect displaced decays of exotic particles produced in the LHC collisions. We also point out how more complicated exotic sectors could evade the BBN lifetime constraints.

New scalars from an extended Higgs sector could have weak scale masses and still have escaped detection. In a type I two Higgs doublet model, for instance, even the charged Higgs can be lighter than the top quark. Because electroweak production of these scalars is modest, the greatest opportunity for their detection might come from rare top decays. For mass hierarchies of the type $m_t>m_{H^{+}}>m_{A^0,H^0}$, the natural signal can arise from top quark pair production, followed by the decay chain $t\to b{H}^{+}$, $H^{+}\to W^{+(*)}{\varphi }^0$, ${\varphi }^0\to b\overline{b},{\tau }^{+}{\tau }^{-}$, where ${\varphi }^0=A^0,H^0$. These final states largely overlap with those of the Standard Model $t\overline{t}{H}_{\mathrm{SM}}$ process, and therefore can potentially contaminate $t\overline{t}{H}_{\mathrm{SM}}$ searches. We demonstrate that existing $t\overline{t}{H}_{\mathrm{SM}}$ analyses can already probe light extended Higgs sectors, and we derive new constraints from their results. Furthermore, we note that existing excesses in $t\overline{t}{H}_{\mathrm{SM}}$ searches can be naturally explained by the contamination of rare top decays to new light Higgses. We discuss how to distinguish this signal from the Standard Model process.

The exclusive production of magnetic monopoles and the bound states of magnetic monopoles (the monopolium) by the photon fusion is considered in different high energy processes. More specifically, we calculate the total cross sections of the ultraperipheral elastic collisions of electron-electron, proton-proton, and lead-lead in present and future colliders, comparing with the previous results found in the literature. Our results indicate that magnetic monopoles or the bound states, if both exist, can be measurable in future electron-electron colliders.

We explore the limits on lepton-flavor universality (LFU) violation in theories where the hierarchy problem is solved by means of a warped extra dimension. In those theories, LFU violation, in fermion interaction with Kaluza-Klein modes of gauge bosons, is provided ab initio when different flavors of fermions are differently localized along the extra dimension. As this fact arises from the mass pattern of quarks and leptons, LFU violation is natural in this class of theories. We analyze the experimental data pointing toward LFU violation, as well as the most relevant electroweak and flavor observables, and the LFU tests in the $\mu /e$ and $\tau /\mu$ sectors. We find agreement with $R_{K^{(*)}}$ and $R_{D^{(*)}}$ data at 95% C.L., provided the third-generation left-handed fermions are composite ($0.14<c_{b_L}<0.28$ and $0.27<c_{{\tau }_L}<0.33$), and find the absolute limits $R_{K^{(*)}}\gtrsim 0.79$ and $R_{D^{(*)}}/R_{D^{(*)}}^{\mathrm{SM}}\lesssim 1.13$. Moreover, we predict $\mathcal{B}(B\to K\nu \overline{\nu })\gtrsim 1.14\times {10}^{-5}$ at 95% C.L., smaller than the present experimental upper bound but a few times larger than the Standard Model prediction.

We present the results of a recent analysis to study the nucleon’s charm sigma term, ${\sigma }_{c\overline{c}}$. We construct a minimal model in terms of light-front variables and constrain the range of possibilities using extant knowledge from deeply inelastic scattering (DIS) and Bayesian parameter estimation, ultimately computing ${\sigma }_{c\overline{c}}$ in an explicitly covariant manner. We find a close correlation between a possible nonperturbative component of the charm structure function, $F_{2,\mathrm{IC}}^{c\overline{c}}$, and ${\sigma }_{c\overline{c}}$. Independent of the prescription for the covariant relativistic quark-nucleon vertex, we determine ${\sigma }_{c\overline{c}}$ under several different scenarios for the magnitude of intrinsic charm in DIS, namely $⟨x{⟩}_{c+\overline{c}}=0.1\%$, 0.35%, and 1%, obtaining for these ${\sigma }_{c\overline{c}}=4\pm 4$, $12\pm 13$, and $32\pm 34\mathrm{MeV}$, respectively. These results imply the existence of a reciprocity between the intrinsic charm parton distribution function and ${\sigma }_{c\overline{c}}$ such that new information from either DIS or improved determinations of ${\sigma }_{c\overline{c}}$ could significantly impact constraints to the charm sector of the proton wave function.

We extend the standard model with two extra Higgs doublets. Making use of a symmetry principle, we present flavor symmetries based on cycle groups $Z_N$ that oblige each Higgs doublet to contribute to the mass of only one generation. The Higgs doublets couple to the fermions with different strengths and in this way accommodate the quark mass hierarchy. We systematically search for all charge configurations that naturally lead to the alignment in flavor space of the quark sectors, resulting in a Cabibbo-Kobayashi-Maskawa matrix near to the identity, determined by the quark mass hierarchy, and with the correct overall phenomenological features. The minimal realization is by the group $Z_7$. We show that only a limited number of solutions exist and that any accidental global symmetry that may occur together with the discrete symmetry is necessarily anomalous. A phenomenological study of each class of solutions concerning predictions to the flavor-changing neutral current phenomena is also performed; for some solutions, it is possible to obtain realistic quark masses and mixing, while the flavor-violating neutral Higgs are light enough to be accessible at the LHC.

We study neutron stars (NSs) in an ungravity (UG) inspired model. We examine the UG effects on the static properties of the selected NSs, in different mass and radius regimes, i.e., ultralow, moderate, and ultrahigh mass NSs, using a polytropic equation of state approach. Based on the observational data, we obtain bounds on the characteristic length and scaling dimension of the UG model. Furthermore, we obtain dynamic properties, such as inertial moment (I), Love number (Love), and quadrupole moment (Q) of a slowly rotating NS in the presence of the exterior gravity and ungravity fields. The UG model is also examined with respect to the I-Love-Q universal relation.

The thermal relic density of dark matter is conventionally set by two-body annihilations. We point out that in many simple models, $3\to 2$ annihilations can play an important role in determining the relic density over a broad range of model parameters. This occurs when the two-body annihilation is kinematically forbidden, but the $3\to 2$ process is allowed; we call this scenario not-forbidden dark matter. We illustrate this mechanism for a vector-portal dark matter model, showing that for a dark matter mass of $m_{\chi }\sim \mathrm{MeV}\text{−}10\mathrm{GeV}$, $3\to 2$ processes not only lead to the observed relic density, but also imply a self-interaction cross section that can solve the cusp/core problem. This can be accomplished while remaining consistent with stringent CMB constraints on light dark matter, and can potentially be discovered at future direct detection experiments.

The growth of a massive black hole will steepen the cold dark matter density at the center of a galaxy into a dense spike, enhancing the prospects for indirect detection. We study the impact of black hole spin on the density profile using the exact Kerr geometry of the black whole in a fully relativistic adiabatic growth framework. We find that, despite the transfer of angular momentum from the hole to the halo, rotation increases significantly the dark matter density close to the black hole. The gravitational effects are still dominated by the black hole within its influence radius, but the larger dark matter annihilation fluxes might be relevant for indirect detection estimates.