A new routine is proposed to relate loop quantum cosmology (LQC) to loop quantum gravity (LQG) from the perspective of effective dynamics. We derive the big-bang singularity resolution and big bounce from the first principle of full canonical LQG. Our results are obtained in the framework of the reduced phase space quantization of LQG. As a key step in our work, we derive with coherent states a new discrete path integral formula of the transition amplitude generated by the physical Hamiltonian. The semiclassical approximation of the path integral formula gives an interesting set of effective equations of motion (EOMs) for full LQG. When solving the EOMs with homogeneous and isotropic ansatz, we reproduce the LQC effective dynamics in the ${\mu }_0$-scheme. The solution replaces the big-bang singularity by a big bounce. In the end, we comment on the possible relation between the $\overline{\mu }$-scheme of effective dynamics and the continuum limit of the path integral formula.

In an earlier short paper [Phys. Rev. Lett. 120, 101301 (2018)], I argued that the horizon-preserving diffeomorphisms of a generic black hole are enhanced to a larger three-dimensional Bondi-Metzner-Sachs symmetry, which is powerful enough to determine the Bekenstein-Hawking entropy. Here, I provide details and extensions of that argument, including a loosening of horizon boundary conditions and a more thorough treatment of dimensional reduction and meaning of a “near-horizon symmetry.”

Behind certain marginally trapped surfaces one can construct a geometry containing an extremal surface of equal, but not larger area. This construction underlies the Engelhardt-Wall proposal for explaining the Bekenstein-Hawking entropy as a coarse-grained entropy. The construction can be proven to exist classically but fails if the null energy condition is violated. Here we extend the coarse-graining construction to semiclassical gravity. Its validity is conjectural, but we are able to extract an interesting nongravitational limit. Our proposal implies Wall’s ant conjecture on the minimum energy of a completion of a quantum field theory state on a half-space. It further constrains the properties of the minimum energy state; for example, the minimum completion energy must be localized as a shock at the cut. We verify that the predicted properties hold in a recent explicit construction of Ceyhan and Faulkner, which proves our conjecture in the nongravitational limit.

We construct the $\mathcal{N}=8$ supersymmetric mechanics with a potential term whose configuration space is the special Kähler manifold of rigid type and show that it can be viewed as the Kähler counterpart of $\mathcal{N}=4$ mechanics related to “curved Witten-Dijkgraaf-Verlinde-Verlinde equations.” Then, we consider the special case of the supersymmetric mechanics with a nonzero potential term defined on the family of $U(1)$-invariant one-(complex)dimensional special Kähler metrics. The bosonic parts of these systems include superintegrable deformations of perturbed two-dimensional oscillators and Coulomb systems.

We present a model for the Universe in which quantum anomalies are argued to play an important dual role: they are responsible for generating matter-antimatter asymmetry in the cosmos, but also provide time-dependent contributions to the vacuum energy density of “running-vacuum” type, which drive the Universe’s evolution. According to this scenario, during the inflationary phase of a string-inspired Universe, and its subsequent exit, the existence of primordial gravitational waves induces gravitational anomalies, which couple to the [Kalb-Ramond (KR)] axion field emerging from the antisymmetric tensor field of the massless gravitational multiplet of the string. Such anomalous $CP$-violating interactions have two important effects. First, they lead to contributions to the vacuum energy density of the form appearing in the “running vacuum model” (RVM) framework, which are proportional to both, the square and the fourth power of the effective Hubble parameter, $H^2$ and $H^4$ respectively. The $H^4$ terms may lead to inflation, in a dynamical scenario whereby the role of the inflaton is played by the effective scalar-field (“vacuumon”) representation of the RVM. Second, there is an undiluted KR axion at the end of inflation, which plays an important role in generating matter-antimatter asymmetry in the cosmos, through baryogenesis via leptogenesis in models involving heavy right-handed neutrinos. As the Universe exits inflation and enters a radiation-dominated era, the generation of chiral fermionic matter is responsible for the cancellation of gravitational anomalies, thus restoring diffeomorphism invariance for the matter/radiation (quantum) theory, as required for consistency. Chiral U(1) anomalies may remain uncompensated, though, during matter/radiation dominance, providing RVM-like $H^2$ and $H^4$ contributions to the Universe energy density. Finally, in the current era, when the Universe enters a de Sitter phase again, and matter is no longer dominant, gravitational anomalies resurface, leading to RVM-like $H^2$ contributions to the vacuum energy density, which are however much more suppressed, as compared to their counterparts during inflation, due to the smallness of the present era’s Hubble parameter $H_0$. In turn, this feature endows the observed dark energy with a dynamical character that follows the RVM pattern, a fact which has been shown to improve the global fits to the current cosmological observations as compared to the concordance $\mathrm{\Lambda }\mathrm{CDM}$ model with its rigid cosmological constant, $\mathrm{\Lambda }>0$. Our model favors axionic dark matter, the source of which can be the KR axion. The uncompensated chiral anomalies in late epochs of the Universe are argued to play an important role in this, in the context of cosmological models characterized by the presence of large-scale cosmic magnetic fields at late eras.

Some cosmological scenarios with bulk viscosity for the dark energy fluid are considered. Based on some considerations related to hydrodynamics, two different equations of state for dark energy are assumed, leading to power-law and logarithmic effective corrections to the pressure. The models are tested with the latest astronomical data from type Ia supernovae (Pantheon sample), measurements of the Hubble parameter $H(z)$, baryon acoustic oscillations and cosmic microwave background radiation. In comparison with the $\mathrm{\Lambda }\mathrm{CDM}$ model, some different results are obtained and their viability is discussed. The power-law model shows some modest results, achieved under negative values of bulk viscosity, while the logarithmic scenario provide good fits in comparison to the $\mathrm{\Lambda }\mathrm{CDM}$ model.

We present a model of $F(R)$ gravity in the presence of a string theory motivated misalignment axion like particle materialized in terms of a canonical scalar field minimally coupled with gravity, and we study the cosmological phenomenology of the model, emphasizing mainly on the late-time era. The main result of the paper is that inflation and the dark energy era may be realized in a geometric way by an $F(R)$ gravity, while the axion is the dark matter constituent of the Universe. The $F(R)$ gravity model consists of an $R^2$ term, which as we show dominates the evolution during the early time, thus producing a viable inflationary phenomenology, and a power law term $\sim R^{\delta }$ with $\delta \ll 1$ and positive, which eventually controls the late-time era. The axion field remains frozen during the inflationary era, which is an effect known for misalignment axions, but as the Universe expands, the axion starts to oscillate, and its energy density scales eventually as we show, as ${\rho }_a\sim a^{-3}$. After appropriately rewriting the gravitational equations in terms of the redshift $z$, we study in detail the late-time phenomenology of the model, and we compare the results with the $\mathrm{\Lambda }\mathrm{CDM}$ model and the latest Planck 2018 data. As we show, the model for small redshifts $0<z<5$ is phenomenologically similar to the $\mathrm{\Lambda }\mathrm{CDM}$ model, however at large redshifts and deeply in the matter domination era, the results are different from those of the $\mathrm{\Lambda }\mathrm{CDM}$ model due to the dark energy oscillations. For the late-time study we investigate the behavior of several well-known statefinder quantities, like the deceleration parameter, the jerk and $Om(z)$, and we demonstrate that the statefinders which contain lower derivatives of the Hubble rate have similar behavior for both the $\mathrm{\Lambda }\mathrm{CDM}$ and the axion $F(R)$ gravity model. We conclude that the axion $F(R)$ gravity model can unify in a geometric way the inflationary epoch with the dark energy era, and with the axion being the main dark matter constituent.

We construct a deformed anti–de Sitter-Einstein-Born-Infeld black hole from noncommutative gauge theory of gravity and determine the metric coefficients up to second order on the noncommutative parameter. We analyze the modifications on the thermodynamical properties of the black hole due to the noncommutative contributions, and we show that noncommutativity has as a direct consequence, the removal of critical points.

We compute the spectrum, mixing and interaction structure of scalar models with a general coupling to the scalar curvature. As it is well known the perturbative states of these theories are given by two massive spin-0 modes in addition to one massless spin-2 state. This latter mode can be identified with the standard graviton field. Indeed, it is possible to define an Einstein frame, where the dynamics of the massless spin-2 graviton is the one associated with the Einstein-Hilbert action. We explore systematically the interactions of all these degrees of freedom in the mentioned frame, since part of the coupling structure can be anticipated by geometrical arguments.

The gravitational wave GW170817 is associated with the inspiral phase of a binary neutron star coalescence event. The LIGO-Virgo detectors’ sensitivity at high frequencies was not sufficient to detect the signal corresponding to the merger and postmerger phases. Hence, the question whether the merger outcome was a prompt black-hole formation or not must be answered using either the premerger gravitational-wave signal or electromagnetic counterparts. In this work we present two methods to infer the probability of prompt black-hole formation, using the analysis of the inspiral gravitational-wave signal. Both methods combine the posterior distribution from the gravitational-wave data analysis with numerical-relativity results. One method relies on the use of phenomenological models for the equation of state and on the estimate of the collapse threshold mass. The other is based on the estimate of the tidal polarizability parameter $\tilde{\mathrm{\Lambda }}$ that is correlated in an equation-of-state agnostic way with the prompt black-hole formation. We analyze GW170817 data and find that the two methods consistently predict a probability of $\sim 50\%–70\%$ for prompt black-hole formation, which however may significantly decrease below 10% if the maximum mass constraint from PSR J0348+0432 or PSR J0740+6620 is imposed.

In presence of gravitational radiation, the notion of angular momentum of an isolated system acquires an infinite dimensional supertranslation ambiguity. This fact has been emphasized in the mathematical general relativity literature over several decades. We analyze the issue in the restricted context of compact binary coalescence (CBC) where the initial total angular momentum of the binary and the final black hole spin generically refer to distinct rotation subgroups of the Bondi-Metzner-Sachs group, related by supertranslations. We show that this ambiguity can be quantified using gravitational memory and the “black hole kick.” Our results imply that, although the ambiguity is conceptually important, under assumptions normally made in the CBC literature, it can be ignored in practice for the current and foreseeable gravitational wave detectors.

The defining feature of a classical black hole is being a perfect absorber. Any evidence showing otherwise would indicate a departure from the standard black-hole picture. Energy and angular momentum absorption by the horizon of a black hole is responsible for tidal heating in a binary. This effect is particularly important in the latest stages of an extreme mass ratio inspiral around a spinning supermassive object, one of the main targets of the future LISA mission. We study how this effect can be used to probe the nature of supermassive objects in a model independent way. We compute the orbital dephasing and the gravitational-wave signal emitted by a point particle in circular, equatorial motion around a spinning supermassive object to the leading order in the mass ratio. Absence of absorption by the central object can affect the gravitational-wave signal dramatically, especially at high spin. This effect will make it possible to put an unparalleled upper bound on the reflectivity of exotic compact objects, at the level of $\mathcal{O}(0.01)\%$. This stringent bound would exclude the possibility of observing echoes in the ringdown of a supermassive binary merger.

We exhibit a Hamiltonian formulation, both for electromagnetism and gravitation, in which it is not required that the Bondi “news” vanish but only that the incoming news be equal to the outgoing ones. This requirement is implemented by defining the fields on a two–sheeted hyperbolic surface, which we term “the hourglass.” It is a spacelike deformation of the complete light cone. On it, one approaches asymptotically (null) past and future infinity while remaining at a fixed (hyperbolic) time, by going to large spatial distances on its two sheets. The Hamiltonian formulation and—in particular—a conserved angular momentum, can only be constructed if one brings in both the electric and magnetic Bondi-Metzner-Sachs (BMS) charges together with their canonically conjugate “memories.” This reveals a close interplay between the BMS and electric-magnetic duality symmetries.

We study gravitational waves emitted by a binary system of nonspinning bodies in a quasicircular inspiral within the framework of Einstein-aether theory. In particular, we compute explicitly and analytically the expressions for the time-domain and frequency-domain waveforms, gravitational wave polarizations, and response functions for both ground- and space-based detectors in the post-Newtonian approximation. We find that, when going beyond the leading order in the post-Newtonian approximation, the non-Einsteinian polarization modes contain terms that depend on both the first and the second harmonics of the orbital phase. We also calculate analytically the corresponding parametrized post-Einsteinian parameters, generalizing the existing framework to allow for different propagation speeds among the scalar, vector, and tensor modes, without assumptions about the magnitude of its coupling parameters, and meanwhile, allowing the binary system to have relative motions with respect to the aether field. Such results allow for the easy construction of Einstein-aether templates that could be used in Bayesian tests of general relativity in the future.

An important property of the three-point functions generated in the early universe is the so-called consistency condition. According to the condition, in the squeezed limit wherein the wave number of one of the three modes (constituting the triangular configuration of wave vectors) is much smaller than the other two, the three-point functions can be completely expressed in terms of the two-point functions. It is found that while the consistency condition is mostly satisfied by the primordial perturbations generated in the inflationary scenario, it is often violated in the bouncing models. The validity of the consistency condition in the context of inflation can be attributed to the fact that the amplitude of the scalar and tensor perturbations freezes on super-Hubble scales. Whereas, in the bouncing scenarios, the amplitude of the scalar and tensor perturbations often grows rapidly as one approaches the bounce, leading to a violation of the condition. In this work, with the help of a specific example involving the tensor perturbations, we explicitly show that suitable nonminimal couplings can restore the consistency condition even in the bouncing models. We briefly discuss the implications of the result.

It is known that a coherently oscillating axion field is a candidate of the dark matter. In the presence of the oscillating axion, the photon can be resonantly produced through the parametric amplification. In the universe, there also exist cosmological magnetic fields which are coherent electromagnetic fields. In the presence of magnetic fields, an axion can be converted into a photon, and vice versa. Thus, it is interesting to investigate what happens for the axion-photon system in the presence of both the axion dark matter and the magnetic fields. This system can be regarded as a coupled system of the axion and the photon whose equations contain the Mathieu type terms. We find that the instability condition is changed in the presence of magnetic fields in contrast to the conventional Mathieu equation. The positions of bifurcation points between stable and unstable are shifted and new instability bands appear. This is because the resonantly amplified axion can be converted to photon, and vice versa.

If dark matter is efficiently captured by a planet, energy released in its annihilation can exceed that planet’s total heat output. Building on prior work, we treat Earth’s composition and dark matter capture in detail and present improved limits on dark matter-nucleon scattering cross sections for dark matter masses ranging from 0.1 to ${10}^{10}\mathrm{GeV}$. We also extend Earth limits by applying the same treatment to Mars. The scope of dark matter models considered is expanded to include spin-dependent nuclear interactions including isospin-independent, proton only, and neutron only interactions. We find that Earth and Mars heating bounds are alleviated for dark matter s-wave self-annihilation cross sections $\lesssim {10}^{-44}{\mathrm{cm}}^2$.

We outline the evaluation of $n$-dimensional fermion traces ($n\in \mathbb{N}$) built by products of Dirac-$\gamma$ matrices suitable for a uniform dimensional continuation. Such a continuation is needed for calculations employing a dimensional regulator whenever intrinsically integer dimensional tensors yield nonvanishing contributions. A prime example for such a tensor is given by ${\gamma }_5$ for $n=4$. The main difference between dimensional regularization (DREG) and a dimensionally continued regularization (DCREG) is that DCREG does not attempt to lift the algebra to continuous $d$ dimensions ($d\in \mathbb{R}$). As a consequence one has to properly deal with evanescent structures in order to ensure the uniform application of the regulator. In basic steps we identify evanescent structures in fermion traces and show that their proper treatment is crucial for example when calculating the $VVA$ anomaly in four dimensions. We checked that the performed considerations enable the evaluation of Standard Model $Z$ factors within DCREG up to including three loops.

We study displaced vertex signatures of long-lived particles (LLPs) from exotic Higgs decays in the context of a Higgs-portal model and a neutral-naturalness model at the circular electron positron collider (CEPC) and future circular collider $e^{+}{e}^{-}$ (FCC-ee). Such two models feature two representative mass ranges for LLPs, which show very different behavior in their decay signatures. The Higgs-portal model contains a very light sub-GeV scalar boson stemming from a singlet scalar field appended to the Standard Model. Such a light scalar LLP decays into a pair of muons or pions, giving rise to a distinctive signature of collimated muon-jet or pion-jet, thanks to the sub-GeV mass. On the other hand, the neutral-naturalness model, e.g., folded supersymmetry, predicts the lightest mirror glueball of mass $O(10)\mathrm{GeV}$, giving rise to long decays with a large transverse impact parameter because of the relatively large mass. Utilizing such distinct characteristics to remove the background, we estimate the sensitivities of searches for light scalar bosons and mirror glueballs at the CEPC and FCC-ee. We find either complementary or stronger coverage compared to the previous results in the similar contexts.

Despite considerable experimental progress large parts of the axionlike particle (ALP) parameter space remain difficult to probe in terrestrial experiments. In some cases, however, small-scale structure of the ALP dark matter (DM) distribution is strongly enhanced, offering opportunities for astrophysical tests. Such an enhancement can be produced by a period of prenucleosynthesis early matter domination (EMD). This cosmology arises in many ultraviolet completions and generates the correct relic abundance for weak coupling $f_a\sim {10}^{16}\mathrm{GeV}$, ALP masses in the range ${10}^{-13}\mathrm{eV}<m_a<1\mathrm{eV}$, and without fine-tuning of the initial misalignment angle. This range includes the QCD axion around ${10}^{-9}-{10}^{-8}\mathrm{eV}$. EMD enhances the growth of ALP small-scale structure, leading to the formation of dense ALP miniclusters which can contain nearly all of DM (depending on ALP mass and reheating temperature). We study the interplay between the initial ALP oscillation, reheating temperature, and effective pressure to provide analytic estimates of the minicluster abundance and properties. ALP miniclusters in the EMD cosmology are denser and more abundant than in $\mathrm{\Lambda }\mathrm{CDM}$. While enhanced substructure generically reduces the prospects of direct detection experiments, we show that pulsar timing and lensing observations can discover these minihalos over a large range of ALP masses and reheating temperatures.