In this paper we consider conformally flat perturbations on the Friedmann-Lemaitre-Robertson-Walker spacetime containing a general matter field. Working with the linearized field equations, we unearth some important geometrical properties of matter shear and vorticity and how they interact with the thermodynamical quantities in the absence of any free gravity powered by the Weyl curvature. As there are hardly any physically realistic rotating exact conformally flat solutions in general relativity, these covariant and gauge invariant results bring out transparently the role of vorticity in the linearized regime. Most interestingly, we demonstrate that the matter shear obeys a transverse traceless tensor wave equation, and the vorticity obeys a vector wave equation in this regime. These shear and vorticity waves replace the gravitational waves in the sense that they causally carry the information about local change in the curvature of these spacetimes. We also look at the heat transport equation in this case and how this varies from the Newtonian case.

Higher-curvature corrections to the effective gravitational action may leave signatures in the spectrum of primordial tensor perturbations if the inflationary energy scale is sufficiently high. In this paper, we further investigate the effects of a coupling of the Inflaton field to higher-curvature tensors in models with a minimal breaking of conformal symmetry. We show that an observable violation of the tensor consistency relation from higher-curvature tensors implies also a relatively large running of the tensor tilt, enhanced even by some order of magnitude with respect to the standard slow-roll case. This may leave signatures in the tensor two-point function that we could test to recognize higher-curvature effects, above all if they are translated into a blue tilted spectrum visible by future gravitational wave experiments. Exploiting current cosmic microwave background and gravitational wave data, we also derive constraints on the inflationary parameters, inferring that large higher-curvature corrections seem to be disfavored.

Product group unification is an attractive alternative to simple grand unification. It solves the infamous doublet-triplet splitting problem and the dimension-5 proton decay problems without introducing any fine-tuning. Furthermore, the matter multiplets are still embedded into unified SU(5) representations. In this paper, we discuss proton decay for the simplest product group unification model based on $\mathrm{SU}(5)\times \mathrm{U}(2{)}_{\mathrm{H}}$. We find that the minimal setup of the model has already been excluded by dimension-6 proton decay. We also show that a simple extension of the model, with naturally generated SU(5) incomplete multiplets, can rectify this problem. We find that the proton lifetime will be in reach of coming experiments like DUNE and Hyper-K, when the mass of the incomplete multiplet is associated with the Peccei-Quinn-symmetry breaking. In this case, the dark matter may be an admixture of the Wino lightest supersymmetric particle and the axion.

Cosmic inflation driven by the vacuum energy associated with the $D$ term of a supersymmetric Abelian gauge group and a possible existence of long-range force mediated by an ultralight gauge boson $Z^{\prime }$ are two extreme examples of models based on extra $U(1)$ symmetries. Large vacuum energy sets the scale of inflation while the scales of long-range forces induced by anomaly free extra gauged $U(1)$ symmetries are constrained by neutrino oscillations, binary pulsar timings, and invisible neutrino decay. There exists a difference of about 40 orders of magnitude between the scales of these two. Also, gauge couplings associated with the long-range forces are very small compared to the standard model couplings and the one required for inflation. We propose a framework based on clockwork mechanism in which these vastly different scales and associated new physics can coexist without invoking any arbitrarily small or large parameter in the fundamental theory. A chain of $U(1)$ is introduced with characteristic nearest-neighbor interactions. A large $D$ term introduced at one end governs the dynamics of inflation. $Z^{\prime }$ is localized on the other end of the chain, and it can be massless or can get naturally suppressed mass. The standard model fields can be charged under one of the intermediate $U(1)\mathrm{s}$ in the chain to give rise to their small effective coupling $g^{\prime }$ with $Z^{\prime }$. Constraints on $g^{\prime }$ and $M_{Z^{\prime }}$ are discussed in the context of the long-range forces of type $L_{\mu }-L_{\tau }$, $L_e-L_{\mu }$, and $B-L$. These, along with the inflation observables, are used to constraint the parameters of the underlying clockwork model.

We propose a practical procedure to extrapolate the spacelike quark propagator onto the complex plane, which follows the Schlessinger point method and the spectral representation of the propagator. As a feasible example, we employ quark propagators for different flavors, obtained from the solutions of their corresponding Dyson-Schwinger equation (DSE), with different truncations. Thus, the analytical structure of the quark propagator is studied, capitalizing on the current-quark mass dependence of the observed features.

In this paper, we study a particular deformation of the Jackiw-Teitelboim gravity recently considered by Maxfield, Turiaci, and independently by Witten. We will compute the partition function of this model as well as its higher order correlators to all orders in genus expansion in the low temperature limit for small perturbations. In this limit, the results match with those obtained from the Airy limit of a Hermitian random matrix ensemble. Using this result, we will also study the free energy of the model. One observes that although the annealed free energy has pathological behaviors, under certain assumptions, the quenched free energy evaluated by replica trick exhibits the desired properties at low temperatures.

We compute the renormalized vacuum polarization for a massless, conformally coupled scalar field on asymptotically anti–de Sitter black hole backgrounds. Mixed (Robin) boundary conditions are applied on the spacetime boundary. We consider black holes with nonspherical event horizon topology as well as spherical event horizons. The quantum scalar field is in the Hartle-Hawking state, and we employ Euclidean methods to calculate the renormalized expectation values. Far from the black hole, we find that the vacuum polarization approaches a finite limit, which is the same for all boundary conditions except Dirichlet boundary conditions.

We explore some (especially, thermodynamical) properties of the dyonic Kerr-Sen-${\mathrm{AdS}}_4$ black hole and its ultraspinning counterpart, and check whether or not both black holes satisfy the first law and Bekenstein-Smarr mass formulas. To this end, new Christodoulou-Ruffini-like squared-mass formulas for the usual dyonic Kerr-Sen-${\mathrm{AdS}}_4$ solution and its ultraspinning cousin are deduced. Similar to the ultraspinning Kerr-Sen-${\mathrm{AdS}}_4$ black hole case, we demonstrate that the ultraspinning dyonic Kerr-Sen-${\mathrm{AdS}}_4$ black hole does not always violate the reverse isoperimetric inequality (RII) since the value of the isoperimetric ratio can either be larger/smaller than, or equal to unity, depending upon the range of the solution parameters, as is the case only with an electric charge. This property is apparently distinct from that of the superentropic dyonic Kerr-Newman-${\mathrm{AdS}}_4$ black hole, which always strictly violates the RII, although both of them have some similar properties in other aspects, such as the horizon geometry and conformal boundary.

Transient non-Gaussian noise in gravitational wave detectors, commonly referred to as glitches, pose challenges for detection and inference of the astrophysical properties of detected signals when the two are coincident in time. Current analyses aim toward modeling and subtracting the glitches from the data using a flexible, morphology-independent model in terms of sine-Gaussian wavelets before the signal source properties are inferred using templates for the compact binary signal. We present a new analysis of gravitational wave data that contain both a signal and glitches by simultaneously modeling the compact binary signal in terms of templates and the instrumental glitches using sine-Gaussian wavelets. The model for the glitches is generic and can thus be applied to a wide range of glitch morphologies without any special tuning. The simultaneous modeling of the astrophysical signal with templates allows us to efficiently separate the signal from the glitches, as we demonstrate using simulated signals injected around real O2 glitches in the two LIGO detectors. We show that our new proposed analysis can separate overlapping glitches and signals, estimate the compact binary parameters, and provide ready-to-use glitch-subtracted data for downstream inference analyses.

Full, nonlinear general relativity predicts a memory effect for gravitational waves. For compact binary coalescence, the total gravitational memory serves as an inferred observable, conceptually on the same footing as the mass and the spin of the final black hole. Given candidate waveforms for any LIGO-Virgo event, then one can calculate the posterior probability distribution functions for the total gravitational memory and use them to compare and contrast the waveforms. In this paper, we present these posterior distributions for the binary black hole merger events reported in the first Gravitational Wave Transient Catalog, using the phenomenological and effective-one-body waveforms. On the whole, the two sets of posterior distributions agree with each other quite well though we find larger discrepancies for the $\ell =2$, $m=1$ mode of the memory. This signals a possible source of systematic errors that was not captured by the posterior distributions of other inferred observables. Thus, the posterior distributions of various angular modes of total memory can serve as diagnostic tools to further improve the waveforms. Analyses such as this would be valuable especially for future events as the sensitivity of ground-based detectors improves, and for LISA which could measure the total gravitational memory directly.

We study thin shells of matter in ($2+1$)-dimensional $F(R)$ theories of gravity with constant scalar curvature $R$. We consider a wide class of spacetimes with circular symmetry, in which a thin shell joins an inner region with an outer one. We analyze the stability of the static configurations under radial perturbations. As examples of spacetimes asymptotically anti–de Sitter, we present a charged bubble and a charged thin shell surrounding a noncharged black hole. In both cases, we show that stable solutions can be found for suitable values of the parameters.

We investigate various dark energy models by taking into account the thermal effects induced from Hawking radiation on the apparent horizon of the Universe, for example, near a finite-time future singularity. If the dark energy density increases as the Universe expands, the Universe’s evolution reaches a type II singularity (or sudden future singularity). The second derivative of the scale factor diverges, but the first derivative remains finite. Quasi–de Sitter evolution can change to sudden future singularity in the case of with an effective cosmological constant larger than the maximum possible value of the energy density of the Universe. Another interesting feature of the cosmological solution is the possibility of a transition between deceleration and acceleration for quintessence dark energy with a simple equation of state. Finally, we investigate which fluid component can remedy big rip singularities and other crushing-type singularities.

We measure the expansion rate of the recent Universe and the calibration scale of the baryon acoustic oscillation (BAO) from low-redshift data. BAO relies on the calibration scale, i.e., the sound horizon at the end of drag epoch $r_d$, which often imposes a prior of the cosmic microwave background (CMB) measurement from the Planck satellite. In order to make really independent measurements of $H_0$, we leave $r_d$ completely free and use the BAO data sets combined with the 31 observational $H(z)$ data, GW170817, and Pantheon sample of Type Ia supernovae. In lambda cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model, we get $H_0=68.63_{-1.77}^{+1.75}\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$, $r_d=146.85_{-3.77}^{+3.29}\mathrm{Mpc}$. For the two model-independent reconstructions of $H(z)$, we obtain $H_0=68.02\pm 1.82\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$, $r_d=148.18_{-3.78}^{+3.36}\mathrm{Mpc}$ in the cubic expansion, and $H_0=68.58\pm 1.76\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$, $r_d=148.02_{-3.60}^{+3.63}\mathrm{Mpc}$ in the polynomial expansion. The values of Hubble constant $H_0$ and sound horizon $r_d$ are consistent with the estimate derived from the Planck CMB data assuming a flat $\mathrm{\Lambda }\mathrm{CDM}$ model, but $H_0$ is in $2.4\sim 2.6$ $\sigma$ tension with SH0ES 2019, respectively.

Upcoming data of the 21-cm hydrogen line during cosmic dawn ($z\sim 10–30$) will revolutionize our understanding of the astrophysics of the first galaxies. Here we present a case study on how to exploit those same measurements to learn about the nature of dark matter (DM) at small scales. Focusing on the effective theory of structure formation (ETHOS) paradigm, we run a suite of simulations covering a broad range of DM microphysics, connecting the output of $N$-body simulations to dedicated 21-cm simulations to predict the evolution of the 21-cm signal across the entire cosmic dawn. We find that observatories targeting both the global signal and the 21-cm power spectrum are sensitive to all ETHOS models we study, and can distinguish them from CDM if the suppression wave number is smaller than $k\approx 300h/\mathrm{Mpc}$, even when accounting for feedback with a phenomenological model. This is an order of magnitude smaller comoving scales than currently constrained by other datasets, including the Lyman-$\alpha$ forest. Moreover, if a prospective 21-cm detection confirmed a deficiency of power at small scales, we show that ETHOS models with strong dark acoustic oscillations can be discriminated from the pure suppression of warm dark matter, showing the power of 21-cm data to understand the behavior of DM at the smallest physical scales.

Chain inflation is an alternative to slow roll inflation in which the Universe undergoes a series of transitions between different vacua. The density perturbations (studied in this paper) are seeded by the probabilistic nature of tunneling rather than quantum fluctuations of the inflaton. We find the scalar power spectrum of chain inflation and show that it is fully consistent with a $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. In agreement with some of the previous literature (and disagreement with others), we show that ${10}^4$ phase transitions per $e$-fold are required in order to agree with the amplitude of cosmic microwave background anisotropies within the observed range of scales. Interestingly, the amplitude of perturbations constrains chain inflation to a regime of highly unstable de Sitter spaces, which may be favorable from a quantum gravity perspective since the swampland conjecture on trans-Planckian censorship is automatically satisfied. We provide new analytic estimates for the bounce action and the tunneling rate in periodic potentials which replace the thin-wall approximation in the regime of fast tunneling. Finally, we study model implications and derive an upper limit of $\sim {10}^{10}\mathrm{GeV}$ on the axion decay constant in viable chain inflation with axions.

The evolution of neutrino flavor in dense environments such as core-collapse supernovae and binary compact object mergers constitutes an important and unsolved problem. Its solution has potential implications for the dynamics and heavy-element nucleosynthesis in these environments. In this paper, we build upon recent work to explore inference-based techniques for the estimation of model parameters and neutrino flavor evolution histories. We combine data assimilation, ordinary differential equation solvers, and neural networks to craft an inference approach tailored for nonlinear dynamical systems. Using this architecture, and a simple two-neutrino-beam, two-flavor model, we compare the performances of nine different optimization algorithms and expand upon previous assessments of the efficacy of inference for tackling problems in flavor evolution. We find that employing this new architecture, together with evolutionary optimization algorithms, accurately captures flavor histories in the small-scale model and allows us to quickly explore both model parameters and initial flavor content. In future work we plan to extend these inference techniques to large numbers of neutrinos.

The future space-based gravitational wave observatory laser interferometer space antenna (LISA) will consist of a constellation of three spacecraft in a triangular constellation, connected by laser interferometers with 2.5 million-kilometer arms. Among other challenges, the success of the mission strongly depends on the quality of the cancellation of laser frequency noise, whose power lies 8 orders of magnitude above the gravitational signal. The standard technique to perform noise removal is time-delay interferometry (TDI). TDI constructs linear combinations of delayed phasemeter measurements tailored to cancel laser noise terms. Previous work has demonstrated the relationship between TDI and principal component analysis (PCA). We build on this idea to develop an extension of TDI based on a model likelihood that directly depends on the phasemeter measurements. Assuming stationary Gaussian noise, we decompose the measurement covariance using PCA in the frequency domain. We obtain a comprehensive and compact framework that we call PCI for “principal component interferometry” and show that it provides an optimal description of the LISA data analysis problem.

Observations of the time-dependent cosmic-ray Sun shadow have been proven as a valuable diagnostic for the assessment of solar magnetic field models. In this paper, seven years of IceCube data are compared to solar activity and solar magnetic field models. A quantitative comparison of solar magnetic field models with IceCube data on the event rate level is performed for the first time. Additionally, a first energy-dependent analysis is presented and compared to recent predictions. We use seven years of IceCube data for the moon and the Sun and compare them to simulations on data rate level. The simulations are performed for the geometrical shadow hypothesis for the moon and the Sun and for a cosmic-ray propagation model governed by the solar magnetic field for the case of the Sun. We find that a linearly decreasing relationship between Sun shadow strength and solar activity is preferred over a constant relationship at the $6.4\sigma$ level. We test two commonly used models of the coronal magnetic field, both combined with a Parker spiral, by modeling cosmic-ray propagation in the solar magnetic field. Both models predict a weakening of the shadow in times of high solar activity as it is also visible in the data. We find tensions with the data on the order of $3\sigma$ for both models, assuming only statistical uncertainties. The magnetic field model CSSS fits the data slightly better than the PFSS model. This is generally consistent with what is found previously by the Tibet $\mathrm{AS}\text{−}\gamma$ Experiment; a deviation of the data from the two models is, however, not significant at this point. Regarding the energy dependence of the Sun shadow, we find indications that the shadowing effect increases with energy during times of high solar activity, in agreement with theoretical predictions.

We present a flexible model to describe the effects of generic deviations of observed gravitational-wave signals from modeled waveforms in the LIGO and Virgo gravitational-wave detectors. With the detection of 11 gravitational-wave events from the GWTC-1 catalog, we are able to constrain possible deviations from our modeled waveforms. In this paper, we present our coherent spline model that describes the deviations, then choose to validate our model on an example phenomenological and astrophysically motivated departure in waveforms based on extreme spontaneous scalarization. We find that the model is capable of recovering the simulated deviations. By performing model comparisons, we observe that the spline model effectively describes the simulated departures better than a normal compact binary coalescence (CBC) model. We analyze the entire GWTC-1 catalog of events with our model and compare it to a normal CBC model, finding that there are no significant departures from the modeled template gravitational waveforms used.

In the constrained sequential dominance (CSD), tri-bimaximal mixing (TBM) pattern in the neutrino sector has been explained, by proposing a certain Yukawa coupling structure for the right-handed neutrinos of the model. However, from the current experimental data it is known that the values of neutrino mixing angles are deviated from the TBM values. In order to explain this neutrino mixing, we first propose a phenomenological model where we consider Yukawa couplings which are modified from that of CSD. Essentially, we add small complex parameters to the Yukawa couplings of CSD. Using these modified Yukawa couplings, we demonstrate that neutrino mixing angles can deviate from their TBM values. We also construct a model, based on a flavor symmetry, in order to justify the modified form of Yukawa couplings of our work.