We present a one-function family of solutions to 4D vacuum Einstein equations. While all diffeomorphic to the same extremal Kerr black hole, they are labeled by well-defined conserved charges and are hence distinct geometries. We show that this family of solutions forms a phase space the symplectic structure of which is invariant under a $U(1)$ Kac-Moody algebra generated by currents ${\mathbb{J}}_n$ and Virasoro generators ${\mathbb{L}}_n$ with central charge six times angular momentum of the black hole. This symmetry algebra is well-defined everywhere in the spacetime, near the horizon or in the asymptotic flat region. Out of the appropriate combination of ${\mathbb{J}}_n$ charges, we construct another Virasoro algebra at the same central charge. Requiring that these two Virasoro algebras should describe the same system leads us to a proposal for identifying extreme Kerr black hole microstates, dubbed as extreme Kerr fluff. Counting these microstates, we not only correctly reproduce the Bekenstein-Hawking entropy of extreme Kerr black hole, but also its expected logarithmic corrections.

We introduce an iterative method to univocally determine the adiabatic expansion of the modes of Dirac fields in spatially homogeneous external backgrounds. We overcome the ambiguities found in previous studies and use this new procedure to improve the adiabatic regularization/renormalization scheme. We provide details on the application of the method for Dirac fields living in a four-dimensional Friedmann-Lemaître-Robertson-Walker spacetime with a Yukawa coupling to an external scalar field. We check the consistency of our proposal by working out the conformal anomaly. We also analyze a two-dimensional Dirac field in Minkowski space coupled to a homogeneous electric field and reproduce the known results on the axial anomaly. The adiabatic expansion of the modes given here can be used to properly characterize the allowed physical states of the Dirac fields in the above external backgrounds.

We consider a theory of scalars minimally coupled to an auxiliary background metric. The theory is generally covariant and subject to the constraint of vanishing energy-momentum tensor. Eliminating the auxiliary metric leads to a reparametrization invariant, nonpolynomial, metric-independent action for the scalar fields. Working in the limit of a large number of physical scalars, a composite massless spin-2 state, the graviton, was identified in previous work, in a two-into-two scalar scattering process. Here, we further explore the possibility that dynamical emergent gravity is a natural feature of generally covariant quantum field theories, by studying the self-interactions of the emergent composite graviton. We show that the fine-tuning previously imposed to ensure the vanishing of the cosmological constant, as well as the existence of the massless spin-2 state, also assures that the emergent graviton’s cubic self-interactions are consistent with those of Einstein’s general relativity, up to higher-derivative corrections. We also demonstrate in a theory with more than one type of scalar that the composite graviton coupling is universal.

It has been recently suggested that oscillons produced in the early universe from certain asymmetric potentials continue to emit gravitational waves for a number of $e$-folds of expansion after their formation, leading to potentially detectable gravitational wave signals. We revisit this claim by conducting a convergence study using graphics processing unit (GPU)-accelerated lattice simulations and show that numerical errors accumulated with time are significant in low-resolution scenarios, or in scenarios where the run-time causes the resolution to drop below the relevant scales in the problem. Our study determines that the dominant, growing high frequency peak of the gravitational wave signals in the fiducial “hill-top model” by Antusch et al., [Phys. Rev. Lett. 118, 011303 (2017).] is a numerical artifact. This finding prompts the need for a more careful analysis of the numerical validity of other similar results related to gravitational waves from oscillon dynamics.

We derive from first principles a third post-Newtonian (3PN) accurate Keplerian-type parametric solution to describe PN accurate dynamics of nonspinning compact binaries in hyperbolic orbits. Orbital elements and functions of the parametric solution are obtained in terms of the conserved orbital energy and angular momentum in both Arnowitt-Deser-Misner-type and modified harmonic coordinates. Elegant checks are provided that include a modified analytic continuation prescription to obtain our independent hyperbolic parametric solution from its eccentric version. A prescription to model gravitational wave polarization states for hyperbolic compact binaries experiencing 3.5PN accurate orbital motion is presented that employs our 3PN accurate parametric solution.

We consider motion in spherically symmetric but time-dependent backgrounds. This problem is of interest, for example, in the context of ultralight dark matter, where galactic haloes produce a time-dependent and periodic gravitational potential. We study the properties of motion of stars in such spacetimes, for different field strengths and frequency, and including dissipative effects. We show that orbital resonances may occur and that spectroscopic emission lines from stars in these geometries exhibit characteristic, periodic modulation patterns. In addition, we work out a fully relativistic and weak-field description of a special class of time-periodic geometries, that of scalar oscillatons. When applied to the galactic center, our results indicate that the motion of S2-like stars may carry distinguishable observational imprints of ultralight dark matter.

We investigate how coherent oscillations backreact on the evolution of the condensate wave function of ultralight axions in the nonrelativistic regime appropriate to cosmic structure formation. The coherent oscillations induce higher harmonics beyond the fundamental mode considered so far when a self-interaction is present, and imprint oscillations in the gravitational potential. We emphasize that the effective self-interaction felt by the slowly-varying envelop of the wave function always differs from the bare Lagrangian interaction potential. We also point out that, in the hydrodynamical formulation of the Gross-Pitaevskii equation, oscillations in the gravitational potential result in an attractive force that counteracts the effect of the quantum pressure arising from the strong delocalization of the particles. Since these effects become significant on physical scales less than the (large) Compton wavelength of the particle, they are presumably not very relevant on the mildly nonlinear scales traced by intergalactic neutral hydrogen for axion masses consistent with the bounds from the Lyman-$\alpha$ forest. However, they might affect the formation of virialized cosmological structures and their stability.

Scalar field theories with ${\mathbb{Z}}_2$ symmetry are the traditional playground of critical phenomena. In this work, these models are studied using functional renormalization group (FRG) equations at order ${\partial }^2$ of the derivative expansion and, differently from previous approaches, the spike plot technique is employed to find the relative scaling solutions in two and three dimensions. The anomalous dimension of the first few universality classes in $d=2$ is given, and the phase structure predicted by conformal field theory is recovered (without the imposition of conformal invariance), while in $d=3$ a refined view of the standard Wilson-Fisher fixed point is found. Our study enlightens the strength of shooting techniques in studying FRG equations, suggesting them as candidates to investigate strongly nonperturbative theories even in more complex cases.

We consider the effects of $R$-parity violation due to the inclusion of a bilinear ${\mu }^{\prime }L{H}_u$ superpotential term in high-scale supersymmetric models with an EeV scale gravitino as dark matter. Although the typical phenomenological limits on this coupling (e.g., due to lepton number violation and the preservation of the baryon asymmetry) are relaxed when the supersymmetric mass spectrum is assumed to be heavy (in excess of the inflationary scale of $3\times {10}^{13}\mathrm{GeV}$), the requirement that the gravitino be sufficiently long lived so as to account for the observed dark matter density, leads to a relatively strong bound on ${\mu }^{\prime }\lesssim 20\mathrm{GeV}$. The dominant decay channels for the longitudinal component of the gravitino are $Z\nu$, $W^{\pm }{l}^{\mp }$, and $h\nu$. To avoid an excess neutrino signal in IceCube, our limit on ${\mu }^{\prime }$ is then strengthened to ${\mu }^{\prime }\lesssim 50\mathrm{keV}$. When the bound is saturated, we find that there is a potentially detectable flux of monochromatic neutrinos with EeV energies.

We develop an effective field theory approach for the $S$-wave quarkonium-nucleon system. We adopt a natural power counting equivalent to Weinberg’s power counting in nucleon-nucleon effective field theories and compute the quarkonium-nucleon potential, scattering length and effective range up to $\mathcal{O}(m_{\pi }^3/{\mathrm{\Lambda }}_{\chi }^3)$ accuracy, including the full light-quark mass dependence. We compare our results with lattice QCD studies of quarkonium-nucleon system, obtain an estimation of the leading order quarkonium-nucleon contact term and determine the $J/\psi$ and ${\eta }_c$ chromopolarizabilities.

In this article, I present a volume average regularization for the second functional derivative operator that appears in the metric-basis Wheeler-DeWitt equation. Naively, the second functional derivative operator in the Wheeler-DeWitt equation is infinite, since it contains terms with a factor of a delta function or derivatives of the delta function. More precisely, the second functional derivative contains terms that are only well defined as a distribution—these terms only yield meaningful results when they appear within an integral. The second functional derivative may, therefore, be regularized by performing an integral average of the distributional terms over some finite volume; I argue that such a regularization is appropriate if one regards quantum general relativity (from which the Wheeler-DeWitt equation may be derived) to be the low-energy effective field theory of a full theory of quantum gravity. I also show that a volume average regularization can be viewed as a natural generalization of the same-variable second partial derivative for an ordinary multivariable function. Using the regularized second functional derivative operator, I construct an approximate solution to the Wheeler-DeWitt equation in the low-curvature, long-distance limit.

We study the cosmology on the Friedmann-Lemaître-Robertson-Walker background in scalar-vector-tensor theories with a broken $U(1)$ gauge symmetry. For parity-invariant interactions arising in scalar-vector-tensor theories with second-order equations of motion, we derive conditions for the absence of ghosts and Laplacian instabilities associated with tensor, vector, and scalar perturbations at linear order. This general result is applied to the computation of the primordial tensor power spectrum generated during inflation as well as to the speed of gravity relevant to the late-time cosmic acceleration. We also construct a concrete inflationary model in which a temporal vector component $A_0$ contributes to the dynamics of cosmic acceleration besides a scalar field $\varphi$ through their kinetic mixings. In this model, we show that all the stability conditions of perturbations can be consistently satisfied during inflation and subsequent reheating.

We study the entropy evolution of black holes in Lovelock gravity by formulating a thermodynamic generalization of the null Raychaudhuri equation. We show that the similarity between the expressions of entropy change of the black hole horizon, due to perturbation, and that of a fluid, which is out of equilibrium, transcends beyond general relativity to the Lovelock class of theories. Exploiting this analogy we find that the shear and bulk viscosities for the black holes in Lovelock theories exactly match with those obtained in the membrane paradigm and also from holographic considerations.

We investigate the effects of a disformal coupling between dark energy and dark matter in the predictions of the spherical collapse and its signatures in galaxy cluster number counts. We find that the disformal coupling has no significant effects on spherical collapse at high redshifts, and in particular during matter domination epoch. However, at lower redshifts, the extrapolated linear density contrast at collapse close to redshift $z\lesssim 1$ and overdensity at virialization can be strongly suppressed by a disformal coupling between dark energy and dark matter. We also find that disformal coupling can have different imprints on cluster number counts compared with conformal coupling, such that the disformal coupling can strongly suppress the predicted number of clusters per redshift interval at $z>0.1$ while enhance the number of cluster at $z<0.05$. Using the specifications of eROSITA survey, we find that the disformal coupling between dark energy and dark matter can be tightly constrained by cluster number counts.

We study stationary, electrically charged fluid structures encircling a rotating compact object with a dipole magnetic field oriented along the rotation axis. This situation is described in an idealized way by the Kerr metric and a magnetic dipole “test” field, that does not affect the spacetime. The self-gravitational and self-electromagnetic field of the fluid are neglected and the fluid is assumed to be nonconductive and in rigid motion. Our work generalizes a previous study by Kovář et al. [1] by taking into account the rotation of the central object. Therefore, we focus on the influence of the rotation onto the existence and position of bound fluid structures. Frame dragging effects allow the existence of polar clouds, which could not be found in nonrotating case. Furthermore counterrotating equatorial tori become more preferred the faster the central object is spinning.

In this paper we develop a formalism for studying the nonrelativistic limit of relativistic field theories in a systematic way. By introducing a simple, nonlocal field redefinition, we transform a given relativistic theory, describing a real, self-interacting scalar field, into an equivalent theory, describing a complex scalar field that encodes at each time both the original field and its conjugate momentum. Our low-energy effective theory incorporates relativistic corrections to the kinetic energy as well as the backreaction of fast-oscillating terms on the behavior of the dominant, slowly varying component of the field. Possible applications of our new approach include axion dark matter, though the methods developed here should be applicable to the low-energy limits of other field theories as well.

Vectorlike quarks (VLQs) are predicted by several theoretical scenarios of new physics and having colour quantum numbers they can copiously be produced at the Large Hadron Collider (LHC) so long that their mass is within the testable kinematic regime of this machine. While it would be convenient to assume that such objects are narrow and can be treated in the so-called narrow width approximation (NWA), this is not always possible: non-minimal new physics scenarios can predict VLQs with potentially large couplings and/or exotic decays, which can contribute to generate a large decay width for such extra quarks without being constrained by current bounds. In this analysis we consider single production of VLQs, which is rapidly becoming a channel of choice in experimental searches owing to the ever increasing limits on their mass, and we describe an approach to treat the large width regime which retains to a large extent a degree of model independence. We also consider the role of potentially sizable and model-dependent interference effects between different VLQ production and decay channels as well as between these and the corresponding irreducible background.

New QCD-like “hypercolor” sectors can generate a broad class of new signatures at hadron colliders and furnish a variety of dark matter candidates. Paired diboson resonances are a particularly important collider signature, arising both from $CP$-conserving vector hypermeson decays of the form $\tilde{\rho }\to \tilde{\pi }\tilde{\pi }\to 4V$ and from $CP$-violating pseudoscalar hypermeson decays of the form $\tilde{\eta }\to \tilde{\pi }\tilde{\pi }\to 4V$. The latter are sensitive to the vacuum angle $\tilde{\theta }$ in the hypercolor sector. We study single- and paired-diboson resonance signatures in final states involving gluons and photons at the LHC and a future 100 TeV $pp$ collider, illustrating the discovery potential at both colliders in simple benchmark models. We also describe some of the theoretical and cosmological consequences of $\tilde{\theta }$. If $CP$-violating hypermeson decays are observable at hadron colliders, ordinary QCD must have an axion. Such scenarios also provide a natural setting for a dark pion component of dark matter, with its relic abundance set by $CP$-violating annihilations. If the new vacuum angle is relaxed to zero by a dark axion, the relic density can instead be a mixture of axions and dark axions. Overproduction of dark axions is most easily avoided if the Universe underwent a period of early matter domination.

We argue that radiative lepton flavor violating (RLFV) decays $P\to \gamma {\ell }_1{\overline{\ell }}_2$ of $P=B_q^0$, ${\overline{D}}^0$, and $K^0$ meson states are robust probes of new physics models. In particular, they could be used to put constraints on the Wilson coefficients of effective operators describing lepton flavor-changing neutral current interactions at low energy scales. We set up a generic framework for describing these transitions and review new physics constraints from $P\to {\ell }_1{\overline{\ell }}_2$ decays. There is discussion of how RLFV transitions provide access to the operators that cannot be constrained in two-body decays and we in turn motivate further experimental searches via these channels.

We propose a new way of explaining the observed Higgs mass, within the cosmological relaxation framework. The key feature distinguishing it from other scanning scenarios is that the scanning field has a noncanonical kinetic term, whose role is to terminate the scan around the desired Higgs mass value. We propose a concrete realization of this idea with two new singlet fields, one that scans the Higgs mass, and another that limits the time window in which the scan is possible. Within the provided time period, the scanning field does not significantly evolve after the Higgs field gets close to the Standard Model value, due to particle production friction.