We investigate three issues that have been discussed in the context of inflation: Fading of the importance of quantum noncommutativity; the phenomenon of quantum squeezing; and the ability to approximate the quantum state by a distribution function on the classical phase space. In the standard treatments, these features arise from properties of mode functions of quantum fields in (near) de Sitter space-time. Therefore, the three notions are often assumed to be essentially equivalent, representing different facets of the same phenomenon. We analyze them in general Friedmann-Lemaître- Robertson-Walker space-times, through the lens of geometric structures on the classical phase space. The analysis shows that: (i) inflation does not play an essential role; classical behavior can emerge much more generally; (ii) the three notions are conceptually distinct; classicality can emerge in one sense but not in another; and, (iii) the third notion is realized in a surprisingly strong sense; there is exact equality between completely general $n$-point functions in the classical theory and those in the quantum theory, provided the quantum operators are Weyl ordered. These features arise already for linear cosmological perturbations by themselves: considerations such as mode-mode coupling, decoherence, and measurement theory—although important in their own right—are not needed for emergence of classical behavior in any of the three senses discussed. Generality of the results stems from the fact that they can be traced back to geometrical structures on the classical phase space, available in a wide class of systems. Therefore, this approach may also be useful in other contexts.

Within cosmological perturbation theory, the cosmic microwave background anisotropies are usually computed from a Boltzmann hierarchy coupled to the perturbed Einstein equations. In this setup, one set of multipoles describes the temperature anisotropies, while two other sets, of electric and magnetic types, describe the polarization anisotropies. In order to reduce the number of multipoles types needed for polarization, and thus to speed up the numerical resolution, an optimal hierarchy has been proposed in the literature for Einstein-Boltzmann codes. However, it has been recently shown that the separability between directional and orbital eigenfunctions employed in the optimal hierarchy is not correct in the presence of spatial curvature. We investigate how the assumption of separability affects the optimal hierarchy and show that it introduces relative errors of order ${\mathrm{\Omega }}_K$ with respect to the full hierarchy. Despite that, we show that the optimal hierarchy still gives extremely good results for temperature and polarization angular spectra, with relative errors that are much smaller than cosmic variance even for curvatures as large as $|{\mathrm{\Omega }}_K|=0.1$. Still, we find that the polarization angular spectra from tensor perturbations are significantly altered when using the optimal hierarchy, leading to errors that are typically of order $50|{\mathrm{\Omega }}_K|\%$ on that component.

We apply a tension metric $Q_{\mathrm{UDM}}$, the update difference in mean parameters, to understand the source of the difference in the measured Hubble constant $H_0$ inferred with cosmic microwave background (CMB) lensing measurements from the Planck satellite ($H_0={67.9}_{-1.3}^{+1.1}\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$) and from the South Pole Telescope ($H_0={72.0}_{-2.5}^{+2.1}\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$) when both are combined with baryon acoustic oscillation (BAO) measurements with priors on the baryon density (BBN). $Q_{\mathrm{UDM}}$ isolates the relevant parameter directions for tension or concordance where the two datasets are both informative and aids in the identification of subsets of data that source the observed tension. With $Q_{\mathrm{UDM}}$, we uncover that the difference in $H_0$ originates from differences between Planck lensing and $\mathrm{BAO}+\mathrm{BBN}$ data, at a probability to exceed of 6.6%. Most of this mild disagreement comes from the galaxy BAO measurements parallel to the line of sight in the redshift range $0.2<z<0.75$. The redshift dependence of the parallel BAOs pulls both the matter density ${\mathrm{\Omega }}_m$ and $H_0$ high in $\mathrm{\Lambda }\mathrm{CDM}$, but these parameter anomalies are usually hidden when the BAO measurements are combined with other cosmological datasets with much stronger ${\mathrm{\Omega }}_m$ constraints.

We perform a joint analysis of the counts and weak lensing signal of redMaPPer clusters selected from the Dark Energy Survey (DES) Year 1 dataset. Our analysis uses the same shear and source photometric redshifts estimates as were used in the DES combined probes analysis. Our analysis results in surprisingly low values for $S_8={\sigma }_8({\mathrm{\Omega }}_{\mathrm{m}}/0.3{)}^{0.5}=0.65\pm 0.04$, driven by a low matter density parameter, ${\mathrm{\Omega }}_{\mathrm{m}}=0.179_{-0.038}^{+0.031}$, with ${\sigma }_8-{\mathrm{\Omega }}_{\mathrm{m}}$ posteriors in $2.4\sigma$ tension with the DES Y1 3x2pt results, and in $5.6\sigma$ with the Planck CMB analysis. These results include the impact of post-unblinding changes to the analysis, which did not improve the level of consistency with other data sets compared to the results obtained at the unblinding. The fact that multiple cosmological probes (supernovae, baryon acoustic oscillations, cosmic shear, galaxy clustering and CMB anisotropies), and other galaxy cluster analyses all favor significantly higher matter densities suggests the presence of systematic errors in the data or an incomplete modeling of the relevant physics. Cross checks with x-ray and microwave data, as well as independent constraints on the observable-mass relation from Sunyaev-Zeldovich selected clusters, suggest that the discrepancy resides in our modeling of the weak lensing signal rather than the cluster abundance. Repeating our analysis using a higher richness threshold ($\lambda \ge 30$) significantly reduces the tension with other probes, and points to one or more richness-dependent effects not captured by our model.

In the event of a gravitational-wave burst candidate, a key question will be which astrophysical signal hypothesis is most likely? Several different gravitational-wave transient sources can be modeled in the Fourier domain using a simple power law. This power-law model provides a reasonable approximation for gravitational-wave bursts from cosmic string cusps, cosmic string kinks, and the memory effect. Each of these sources is described using a different spectral index. In this work, we simulate interferometer strain data with injections of memory and other power-law bursts to demonstrate model selection in support of signal detection and for use in parameter estimation. We show how Bayesian inference can be used to measure the power-law spectral index, thereby distinguishing between different astrophysical scenarios. We propose a strategy for model selection of power-law burst signals for gravitational-wave candidates, and we aim to use this analysis to determine whether a specific candidate can be best described by a compact binary coalescence (CBC) signal or by some other interesting astrophysical mechanism.

We study the effects of custodial symmetry violation in the Georgi-Machacek (GM) model. The GM model adds isospin-triplet scalars to the Standard Model in a way that preserves custodial symmetry at tree level; however, this custodial symmetry has long been known to be violated at the one-loop level by hypercharge interactions. We consider the custodial-symmetric GM model to arise at some high scale as a result of an unspecified ultraviolet completion and quantify the custodial symmetry violation induced as the model is run down to the weak scale. The measured value of the electroweak $\rho$ parameter (along with perturbative unitarity) lets us constrain the scale of the ultraviolet completion to lie below tens to hundreds of tera-electron volts (TeV) over almost all of the parameter space. Subject to this constraint, we quantify the size of other custodial-symmetry-violating effects at the weak scale, including custodial symmetry violation in the couplings of the 125 GeV Higgs boson to $W$ and $Z$ boson pairs and mixings and mass splittings among the additional Higgs bosons in the theory. We find that these effects are small enough that they are unlikely to be probed by the Large Hadron Collider (LHC), but may be detectable at a future $e^{+}{e}^{-}$ collider. We note that the upper bound on the scale of the ultraviolet completion is large enough that virtual effects from the ultraviolet completion will also be undetectable at the LHC. This means that the GM model is a valid effective theory for LHC physics.

Supersymmetric Yang-Mills (SYM) theories in four dimensions exhibit many interesting nonperturbative phenomena that can be studied by means of Monte Carlo lattice simulations. However, the lattice regularization breaks supersymmetry explicitly, and in general a fine-tuning of a large number of parameters is required to correctly extrapolate the theory to the continuum limit. From this perspective, it is important to preserve on the lattice as many symmetries of the original continuum action as possible. Chiral symmetry for instance prevents an additive renormalization of the fermion mass. A (modified) version of chiral symmetry can be preserved exactly if the Dirac operator fulfills the Ginsparg-Wilson relation. In this contribution, we present an exploratory nonperturbative study of $\mathcal{N}=1$ supersymmetric Yang-Mills theory using the overlap formalism to preserve chiral symmetry at nonzero lattice spacings. $\mathcal{N}=1$ SYM is an ideal benchmark toward the extension of our studies to more complex supersymmetric theories, as the only parameter to be tuned is the gluino mass. Overlap fermions allow us therefore to simulate the theory without fine-tuning. We compare our approach to previous investigations of the same theory, and we present clear evidences for gluino condensation.

We calculate the helicity amplitudes for scattering of a quark from both large and small $x$ gluons of a target proton or nucleus using spinor helicity formalism. We show that scattering from large $x$ gluons of the target results in nonzero spin asymmetry at intermediate $p_t$ as well as rapidity loss of the projectile quark. We comment on how this can also generate angular asymmetries in particle production in high energy collisions.

The forward doubly-virtual Compton scattering (VVCS) off the nucleon contains a wealth of information on nucleon structure, relevant to the calculation of the two-photon-exchange effects in atomic spectroscopy and electron scattering. We report on a complete next-to-leading-order (NLO) calculation of low-energy VVCS in chiral perturbation theory ($\chi \mathrm{PT}$). Here we focus on the unpolarized VVCS amplitudes $T_1(\nu ,Q^2)$ and $T_2(\nu ,Q^2)$, and the corresponding structure functions $F_1(x,Q^2)$ and $F_2(x,Q^2)$. Our results are confronted, where possible, with “data-driven” dispersive evaluations of low-energy structure quantities, such as nucleon polarizabilities. We find significant disagreements with dispersive evaluations at very low momentum-transfer $Q$; for example, in the slope of polarizabilities at zero momentum transfer. By expanding the results in powers of the inverse nucleon mass, we reproduce the known “heavy-baryon” expressions. This serves as a check of our calculation, as well as demonstrates the differences between the manifestly Lorentz-invariant ($\mathrm{B}\chi \mathrm{PT}$) and heavy-baryon ($\mathrm{HB}\chi \mathrm{PT}$) frameworks.

In this paper, we studied systematically the semileptonic decays ${\overline{B}}_s\to K^{(*)}{\ell }^{+}{\ell }^{-}$ with $l^{-}=(e^{-},{\mu }^{-},{\tau }^{-})$ by using the perturbative QCD (PQCD) and the “$\mathrm{PQCD}+\mathrm{Lattice}$” factorization approach, respectively. We first evaluated all relevant form factors $F_i(q^2)$ in the low-$q^2$ region using the PQCD approach, and we also took the available lattice QCD results at the end point $q_{\max }^2$ as additional inputs to improve the extrapolation of the form factors to the high-$q^2$ region. We calculated the branching ratios and twelve other kinds of physical observables. From our studies, we find the following points: (a) for ${\overline{B}}_s\to K{l}^{+}{l}^{-}$ decays, the PQCD and $\mathrm{PQCD}+\mathrm{Lattice}$ predictions for branching ratios $\mathcal{B}({\overline{B}}_s\to K{l}^{+}{l}^{-})$, the ratios of the branching ratios $R_K^{e\mu }$ and $R_K^{\mu \tau }$, and the longitudinal polarization asymmetry of the leptons $P_L$ agree well within errors; (b) the PQCD and $\mathrm{PQCD}+\mathrm{Lattice}$ predictions for the $CP$-averaged branching ratio $\mathcal{B}({\overline{B}}_s\to K^{*}{\mu }^{+}{\mu }^{-})$ are $(3.17_{-0.78}^{+0.95})\times {10}^{-8}$ and $(2.48_{-0.50}^{+0.56})\times {10}^{-8}$ respectively, which agree well with the LHCb measured value $(2.9\pm 1.1)\times {10}^{-8}$ and the light-cone sum rule prediction; (c) for the ratios $R_{K^{*}}^{e\mu }$ and $R_{K^{*}}^{\mu \tau }$, the PQCD and $\mathrm{PQCD}+\mathrm{Lattice}$ predictions agree well with each other and have a small error less than 10%; (d) for the direct $CP$ asymmetries ${\mathcal{A}}_{CP}$ of all considered decay modes, they are always very small as expected: less than 5% in magnitude; (e) for the angular observables $P_{1,2,3}$ and $P_{4,5,6,8}^{\prime }$, our theoretical predictions for each kind of lepton are consistent within errors; (f) the theoretical predictions of the angular observables $P_3$ and $P_6^{\prime }$ are less than ${10}^{-2}$ in size, but the magnitude of $P_{1,2}$ and $P_{4,5}^{\prime }$ are larger than 0.2; and (g) the PQCD and $\mathrm{PQCD}+\mathrm{Lattice}$ predictions of the binned values of all considered observables in the two $q^2$ bins $[0.1–0.98]{\mathrm{GeV}}^2$ and $[1.1–6]{\mathrm{GeV}}^2$ generally agree with each other and are also consistent with the light-cone sum rule results within errors. We believe that above predictions could be tested by future LHCb and Belle-II experiments.

In this paper we consider the $\mathbb{C}{P}^{N-1}$ model confined to an interval of finite size at finite temperature and chemical potential. We obtain, in the large-$N$ approximation, a mixed-gradient expansion of the one-loop effective action of the order parameter associated with the effective mass of the quantum fluctuations. This expansion gives an expression for the thermodynamic potential density as a functional of the order parameter, generalizing previous calculations to arbitrarily large order and to the case of finite chemical potential and allows one to discuss some generic features of the ground state of the model. The technique used here relies on analytic regularization and provides an efficient scheme to extract the coefficients of the expansion. Once a solution for the ground state is known these coefficients can be used to deduce some generic properties of the ground state as a function of external conditions. We also show that there can be no transition to a massless phase for any value of the external conditions considered and clarify a seemingly important point regarding the regularization of the effective action connected to the appearance of logarithmic divergences and to the Mermin-Wagner-Hoenberg-Coleman theorem.

We study behavior of the critical $O(N)$ vector model with quartic interaction in $2\le d\le 6$ dimensions to the next-to-leading order in the large-$N$ expansion. We derive and perform consistency checks that provide an evidence for the existence of a nontrivial fixed point and explore the corresponding conformal field theory (CFT). In particular, we use conformal techniques to calculate the multiloop diagrams up to and including 4 loops in general dimension. These results are used to calculate a new CFT data associated with the three-point function of the Hubbard-Stratonovich field. In $6-\epsilon$ dimensions our results match their counterparts obtained within a proposed alternative description of the model in terms of $N+1$ massless scalars with cubic interactions. In $d=3$ we find that the operator product expansion coefficient vanishes up to $\mathcal{O}(1/N^{3/2})$ order.

The ladder operators in harmonic oscillators are a well-known strong tool for various problems in physics. In the same sense, it is sometimes expected to handle the problems of repulsive harmonic oscillators in a similar way to the ladder operators in harmonic oscillators, though their analytic solutions are well known. In this paper, we discuss a simple algebraic way to introduce the ladder operators of the repulsive harmonic oscillators, which can reproduce well-known analytic solutions. Applying this formalism, we discuss the charged particles in a constant electric field in relation to the Schwinger effect; the discussion is also made on a supersymmetric extension of this formalism.

A black hole that is ringing down to quiescence emits gravitational radiation of a very specific nature that can inform us of its mass and angular momentum, test the no-hair theorem for black holes, and perhaps even give us additional information about its progenitor system. This paper provides a detailed description of, and investigation into the behavior of, multimode fitting of the ringdown signal provided by numerical simulations. We find that there are at least three well-motivated multimode fitting schemes that can be used. These methods are tested against a specific numerical simulation to allow for comparison to prior work.

By using complex angular momentum techniques, we study the electromagnetic radiation generated by a charged particle falling radially from infinity into a Schwarzschild black hole. We consider both the case of a particle initially at rest and that of a particle projected with a relativistic velocity and we construct complex angular momentum representations and Regge pole approximations of the partial wave expansions defining the Maxwell scalar ${\varphi }_2$ and the energy spectrum $dE/d\omega$ observed at spatial infinity. We show, in particular, that Regge pole approximations involving only one Regge pole provide effective resummations of these partial wave expansions permitting us (i) to reproduce with very good agreement the black hole ringdown without requiring a starting time, (ii) to describe with rather good agreement the tail of the signal and sometimes the preringdown phase, and (iii) to explain the oscillations in the electromagnetic energy spectrum radiated by the charged particle. The present work as well as a previous one concerning the gravitational radiation generated by a massive particle falling into a Schwarzschild black hole [A. Folacci and M. Ould El Hadj, Phys. Rev. D 98, 064052 (2018)] highlight the benefits of studying radiation from black holes in the complex angular momentum framework (they obviously appear when the approximations obtained involve a small number of Regge poles and have a clear physical interpretation) but also to exhibit the limits of this approach (this is the case when it is necessary to take into account background integral contributions).

We propose a regularization procedure for the novel Einstein-Gauss-Bonnet theory of gravity, which produces a set of field equations that can be written in closed form in four dimensions. Our method consists of introducing a counterterm into the action, and does not rely on the embedding or compactification of any higher-dimensional spaces. This counterterm is sufficient to cancel the divergence in the action that would otherwise occur, and exactly reproduces the trace of the field equations of the original formulation of the theory. All other field equations display an extra scalar gravitational degree of freedom in the gravitational sector, in keeping with the requirements of Lovelock’s theorem. We discuss issues concerning the equivalence between our new regularized theory and the original.

To inherit more features of full loop quantum Brans-Dicke theory, the Euclidean and Lorentzian terms of the Hamiltonian constraint are quantized independently in loop quantum Brans-Dicke cosmology. An alternative Hamiltonian constraint operator and its effective expression are obtained in the cosmological model. A residual quantum correction term is found in the effective Hamiltonian constraint, which has no analog in the effective Hamiltonian of the loop quantum cosmology from general relativity. The dynamics driven by this effective Hamiltonian constraint is analyzed in detail. For the physically interesting case of $\omega \gg 1$, this effective Hamiltonian drives a bouncing evolution which evolves from a de Sitter universe to a classical Brans-Dicke solution.

The ringdown is the late part of the postmerger signature emitted during the coalescence of two black holes and comprises a superposition of quasinormal modes. Within the general theory of relativity, the no-hair theorem for black holes states that the frequencies and the damping times of these modes are entirely determined by the mass and the angular momentum of the final Kerr black hole. Detection of multiple ringdown modes in the gravitational wave signal emitted during a binary black hole coalescence would allow us to validate the no-hair theorem with observations. The signal-to-noise ratio of the black hole ringdown and the amplitude of the subdominant modes to the dominant mode determine the detectability of the subdominant mode. We use Bayesian inference to investigate the interplay between these two factors towards their detectability. We systematically vary the two factors in a set of simulated analytical ringdown signals to infer the minimum signal-to-noise ratio needed in a ringdown signal for performing black hole spectroscopy. Our estimates on the minimum signal strength required to perform black hole spectroscopy as a function of amplitude ratio allows us to gain insight into the kind of signals that will be promising for black hole spectroscopy.

We study the late cosmological evolution, from the nonrelativistic matter dominated era to the dark energy era, in modified gravity models described by degenerate higher-order scalar-tensor (DHOST) theories. They represent the most general scalar-tensor theories propagating a single scalar degree of freedom and include Horndeski and beyond Horndeski theories. We provide the homogeneous evolution equations for any quadratic DHOST theory, without restricting ourselves to theories where the speed of gravitational waves coincides with that of light since the present constraints apply to wavelengths much smaller than cosmological scales. To illustrate the potential richness of the cosmological background evolution in these theories, we consider a simple family of shift-symmetric models, characterized by three parameters and compute the evolution of dark energy and of its equation of state. We also identify the regions in parameter space where the models are perturbatively stable.