Significant disturbances in the test masses, arising from unforeseen instrument anomalies during scientific measurements, have a considerable impact on space-borne gravitational wave detection. Therefore, exploring effective data processing methods to mitigate these effects is of crucial importance. In a pioneering effort, previous literature proposed the use of time-delay interferometry for this purpose and developed a first-generation combination to mitigate disturbances from two test masses on the same spacecraft. However, due to its inherent limitations in suppressing laser phase noise, it is not suitable for actual data processing in space-borne gravitational wave detection. This paper aims to devise a comprehensive approach to derive more practical second-generation time-delay interferometry combinations. The technique was initially developed for laser phase noise suppression. Specifically, laser interference data streams between and within satellites are preprocessed to form six synthetic data streams, which contain three laser phase noises. Then, time-delay interferometry combinations are applied to these six data streams to construct virtual equal-arm interference, thereby suppressing the three laser phase noises. This process leaves two degrees of freedom, which can be strategically used to reduce one or two major disturbances in the test masses. Therefore, we used an algebraic approach to construct the necessary constraint equations. From these, we derived more practical second-generation time-delay interferometry combinations capable of simultaneously suppressing laser phase noise and disturbances from two test masses, either within one spacecraft or across two spacecraft. In addition, for acquiring second-generation time-delay interferometry combinations, both the geometric approach and the combinatorial algebraic approach have been proven effective. The former utilizes the synthesis of virtual optical paths, which have intuitive physical interpretations, while the latter employs algebraic methods to solve equations with some constraints. However, it is found that the combinatorial algebraic approach, as well as second-generation geometric combinations of length not exceeding 16 links, cannot address all scenarios of the test mass anomalies. This work provides a strategy for addressing large disturbances from partial test masses in space-borne gravitational wave detection from a data processing perspective, thereby contributing to the implementation of the detection task.

It is a common belief that a theory of quantum gravity should ultimately cure curvature singularities which are inevitable within general relativity, and plague for instance the Schwarzschild and Kerr metrics, usually considered as prototypes for primordial black holes (PBHs) as dark matter (DM) candidates. We continue our study, initiated in a companion paper, of nonsingular objects as PBHs, considering three regular non-$tr$ (non-time-radial)-symmetric metrics, all of which are one-parameter extensions of the Schwarzschild space-time: the Simpson-Visser, Peltola-Kunstatter, and D’Ambrosio-Rovelli space-times, with the latter two motivated by loop quantum gravity. We study evaporation constraints on PBHs described by these regular metrics, deriving upper limits on $f_{\mathrm{pbh}}$, the fraction of DM in the form of PBHs. Compared to their Schwarzschild counterparts, these limits are weaker, and result in a larger asteroid mass window where all the DM can be in the form of PBHs, with the lower edge moving potentially more than an order of magnitude. Our work demonstrates as a proof-of-principle that quantum gravity-inspired space-times can simultaneously play an important role in the resolution of singularities and in the DM problem.

Primordial black holes (PBHs) are usually assumed to be described by the Schwarzschild or Kerr metrics, which however feature unwelcome singularities. We study the possibility that PBHs are nonsingular objects, considering three phenomenological, regular tr (time-radial)-symmetric space-times (including the well-known Bardeen and Hayward ones), featuring either de Sitter or Minkowski cores. We characterize the evaporation of these PBHs and constrain their abundance from $\gamma$-ray observations. For all three metrics we find that constraints on $f_{\mathrm{pbh}}$, the fraction of dark matter (DM) in the form of PBHs, weaken with respect to the Schwarzschild limits, because of modifications to the PBH temperature and graybody factors. This moves the lower edge of the asteroid mass window down by potentially an order of magnitude or more, leading to a much larger region of parameter space where PBHs can make up all the DM. A companion paper is devoted to non-tr-symmetric metrics, including loop quantum gravity-inspired ones. Our work provides a proof-of-principle for the interface between the DM and singularity problems being a promising arena with a rich phenomenology.

Pixelated dark energy is a string theory scenario with a quantum mechanically stable cosmological constant. The number of pixels that make up the universe slowly increases, manifesting as a time-dependent source of dark energy. DESI has recently reported evidence for dynamical dark energy that fits within this framework. In light of this, we perform the first cosmological analysis of the pixelated model. We find that the simplest model where the pixel growth rate is constant is able to accommodate the data, providing a marginally better fit than $\mathrm{\Lambda }\mathrm{CDM}$; and we show that models where the pixel growth rate is increasing and of order the Hubble constant today could provide better fits. Our analysis helps to clarify the features of UV constructions of dark energy necessary to accommodate the data.

Primordial black holes (PBHs) are the natural candidate of dark matter (DM) as they only interact gravitationally and can evade any experiments on earth. In the standard semiclassical calculation of Hawking radiation, PBHs with mass below ${10}^{15}\mathrm{g}$ evaporated by now and therefore cannot be DM. However, the recently discovered quantum memory burden effect can significantly suppress the evaporation of PBHs after the half-decay time. This quantum effect could open up a new mass window below ${10}^{10}\mathrm{g}$ where PBHs can still exist today and be DM. In this paper, we compute the gravitational wave (GW) signals associated with the formation of PBHs in this new mass window. We consider two formation scenarios: PBHs formed from inflationary perturbation and PBHs formed from collapse of Fermi-balls in a first-order phase transition (FOPT). GWs produced from these two scenarios have distinct features and, while the GW from inflation peaks at high frequency, the GW from FOPT peaks at lower frequency that can be within the reach of future experiments.

The large-scale structure of the Universe is well approximated by the Friedmann equations, parametrized by several energy densities which can be observationally inferred. A natural question to ask is: How different would the Universe be if these densities took on other values? While there are many ways this can be approached depending on interpretation and mathematical rigor, we attempt an answer by building a “history space” of different cosmologies. A metric is introduced after overcoming technical hurdles related to Lorentzian signature and infinite volume, at least for topologically closed cases. Geodesics connecting two points on the superspace are computed to express how distant—in a purely geometric sense—two universes are. Age can be treated as a free parameter in such an approach, leading to a more general mathematical construct relative to geometrodynamical configuration space. Connections to bubble inflation and phase transitions are explored.

Multipole expansions have been often used for extracting cosmological information from anisotropic quantities in observation. However, which basis of the expansion is best suited to quantify the anisotropies is not a trivial question in any summary statistics. In this paper, using the Fisher matrix formalism, we investigate the information content in multipole moments of the power spectra of galaxy density and intrinsic ellipticity fields in linear theory from the Alcock-Paczynski effect and redshift-space distortions (RSD). We consider two expansion schemes, the associated Legendre basis as well as the standard Legendre basis conventionally used in literature. We find that the information in the multipoles of the intrinsic alignment (IA) power spectra in the associated Legendre basis converges more slowly to that in the full 2D power spectra than in the Legendre basis. This trend is particularly significant when we consider a high number density sample. In this high number density case, we show that the errors on the Hubble parameter obtained from the multipoles of the IA cross- and autopower spectra in the associated Legendre basis are respectively about 6% and 10% larger than the full 2D case even when we use multipoles up to $\ell =6$. Our results demonstrate that the choice of basis is arbitrary but changes the information content encoded in multipoles depending on the sample and statistics under consideration.

The Hubble tension is inherently multidimensional and bears important implications for parameters beyond $H_0$. We discuss the key role of the matter density parameter ${\mathrm{\Omega }}_m$ and the physical cold dark matter density ${\omega }_c$. We argue that once ${\mathrm{\Omega }}_m$ and the physical baryon density ${\omega }_b$ are calibrated, through baryon acoustic oscillations (BAO) and/or type Ia supernovae (SNeIa) for ${\mathrm{\Omega }}_m$, and via big bang nucleosynthesis for ${\omega }_b$, any model raising $H_0$ requires raising ${\omega }_c$ and, under minimal assumptions, also the clustering parameter $S_8$. We explicitly verify that this behavior holds when analyzing recent BAO and SNeIa data. We argue that a calibration of ${\mathrm{\Omega }}_m$ as reliable and model-independent as possible should be a priority in the Hubble tension discussion, and an interesting possibility in this sense could be represented by galaxy cluster gas mass fraction measurements.

We extend our previous work [Proukakis et al., Unified description of corpuscular and fuzzy bosonic dark matter, Phys. Rev. D 108, 083513 (2023)] on the dynamics of bosonic, nonrelativistic and self-interacting dark matter that simultaneously contains both a “fuzzy” low-momentum component and one with higher momenta that may be well approximated as a collection of distinct particles and described by a corresponding phase-space distribution. Starting from the nonrelativistic Schwinger-Keldysh action and working beyond leading-order in the Keldysh basis fields, encoding stochastic fluctuations of the slow modes and all fluctuations of the fast modes, we obtain stochastic self-consistently coupled Gross-Pitaevskii, collisional Boltzmann kinetic and Poisson equations. Our final set of equations, which feature various collisional (dissipative and scattering) contributions and two corresponding independent stochastic force terms, are consistent with generalized fluctuation-dissipation type relations in the limit of thermal equilibrium between the particles.

Some cosmic microwave background (CMB) data allow a cosmological scenario in which the free streaming of neutrinos is delayed until close to matter-radiation equality. Interestingly, recent analyses have revealed that large-scale structure (LSS) data also align with this scenario, discarding the possibility of an accidental feature in the CMB sky and calling for further investigation into the free-streaming nature of neutrinos. By assuming a simple representation of self-interacting neutrinos, we investigate whether this nonstandard scenario can accommodate a consistent cosmology for both the CMB power spectra and the large-scale distribution of galaxies simultaneously. Employing three different approaches—a profile likelihood exploration, a nested sampling method, and a heuristic Metropolis-Hasting approximation—we exhaustively explore the parameter space and demonstrate that galaxy data exacerbates the challenge already posed by the Planck polarization data for this nonstandard scenario. We find that the Bayes factor disfavor strong interactions among neutrinos over the $\mathrm{\Lambda }\mathrm{CDM}$ and $\mathrm{\Lambda }\mathrm{CDM}+N_{\mathrm{eff}}+\sum m_{\nu }$ models with odds of $7:10,000$ and $23:1000$, respectively, providing large evidence against the simple self-interacting neutrino model. Our analysis emphasizes the need to consider a broader range of phenomenologies in the early Universe. We also highlight significant numerical and theoretical challenges ahead in uncovering the exact nature of the feature observed in the data or, ultimately, confirming the standard chronological evolution of the Universe.

Future low-noise cosmic microwave background (CMB) lensing measurements from e.g., CMB-S4 will be polarization dominated, rather than temperature dominated. In this new regime, statistically optimal lensing reconstructions outperform the standard quadratic estimator, but their sensitivity to extragalactic polarized foregrounds has not been quantified. Using realistic simulations of polarized radio and infrared point sources, we show for the first time that optimal Bayesian lensing from a CMB-S4-like experiment is insensitive to the expected level of polarized extragalactic foregrounds after masking, as long as an accurate foreground power spectrum is included in the analysis. For more futuristic experiments where these foregrounds could cause a detectable bias, we propose a new method to jointly fit for lensing and the Poisson foregrounds, generalizing the bias hardening from the standard quadratic estimator to Bayesian lensing.

Long and short gamma-ray bursts (GRBs) are thought to arise from different and unrelated astrophysical progenitors. The association of long GRBs with supernovae (SNe) and the difference in the distributions of galactocentric offsets of long and short GRBs within their host galaxies have often been considered strong evidence of their unrelated origins. Long GRBs have been thought to result from the collapse of single massive stars, while short GRBs come from mergers of compact-object binaries. Our present study challenges this conventional view. We demonstrate that the observational properties, such as the association with SNe and the different galactic offsets, are naturally explained within the framework of the binary-driven hypernova model, suggesting an evolutionary connection between long and short GRBs.

Stochastic gravitational waves (GWs) consist of a primordial component from early Universe processes and an astrophysical component from compact binary mergers. To detect the primordial stochastic GW background (SGWB), the astrophysical foregrounds must be reduced to high precision, which is achievable for third-generation (3G) ground based GW detectors. Previous studies have shown that the foreground from individually detectable merger events can be reduced with fractional residual energy density below ${10}^{-3}$, and the residual foreground from subthreshold binary neutron stars (BNSs) will be the bottleneck if not well cleaned. In this work, we propose that the foreground energy density of subthreshold BNSs ${\mathrm{\Omega }}_{\mathrm{sub}}$ can be estimated via a population based approach from the individually detectable BNSs utilizing the isotropic orbital orientations of all BNSs, i.e., uniform distribution in $\cos \iota$, where $\iota$ is the BNS inclination angle with respect to the line of sight. Using this approach, we find ${\mathrm{\Omega }}_{\mathrm{sub}}$ can be measured with percent-level uncertainty, assuming $O({10}^5)$ individually detected BNSs in our simulations. This method represents a promising approach to tackling the foreground cleaning problem.

We study the effects of magnetic field in the formation of a radiatively inefficient accretion flow in the presence of Bremsstrahlung cooling, which facilitates the formation of a geometrically thin, optically thick accretion disk surrounded by a hot corona. We have performed axis-symmetric magnetohydrodynamic simulations of an initial accretion torus with a $1/r$ dependant local poloidal field in the presence of a pseudo-Newtonian potential, taking into account optically thin cooling, resistivity, and viscosity. We observe the formation of persistent jets and magnetized outflows from the corona surrounding a thin disk with an increase in the magnetic diffusivity parameter. We have defined an equivalent timescale (${\tau }_{eq}$) which takes into account the heating timescales due to viscosity, resistivity, magnetic reconnection, and magnetorotational instability turbulence such that the thin disk is formed if the cooling timescale (${\tau }_{\mathrm{cool}}$) is lower than this equivalent timescale (${\tau }_{\mathrm{cool}}/{\tau }_{eq}<1$). Using this condition, for the first time, we found that the thin disk exists when the initial ratio of plasma pressure to magnetic pressure (plasma beta) exceeds a range of 600–800 for the gas obeying a polytropic equation of state accreting at ${10}^{-5}{M}_{\odot }/\mathrm{yr}$.

Magnetars are neutron stars with superstrong magnetic fields. Some of them (soft-gamma repeaters, SGRs) demonstrate gigantic flares whose nature is still unclear. At the decay phase of such flares, one often observes quasiperiodic oscillations (QPOs), which are treated as stellar oscillations triggered by the flares. We study, for the first time, magnetoelastic oscillations of magnetars possessing toroidal magnetic fields confined in the stellar crust, without imposing axial symmetry of perturbations. We show that the Zeeman effect makes the oscillation spectrum much richer than for axially symmetric oscillations. The main properties of theoretical QPO spectra are discussed, as well as their potential to interpret observations and explore magnetar physics.

We study from the theoretical point of view the ${\mathrm{\Lambda }}_c^{+}\to {\pi }^{+}\eta \mathrm{\Lambda }$ reaction, recently measured by the Belle and BESIII Collaborations, where clear signals are observed for $a_0(980)$, $\mathrm{\Lambda }(1670)$, and $\mathrm{\Sigma }(1385)$ excitation. By considering the $a_0(980)$ and $\mathrm{\Lambda }(1670)$ as dynamically generated resonances from the meson meson and meson baryon interaction, respectively, we are able to determine their relative production strengths in the reaction, which is also tied to the strength of the ${\pi }^{+}\eta \mathrm{\Lambda }$ tree level contribution. We observe that this latter strength is very big and there are large destructive interferences between the tree level and the rescattering terms where the $a_0(980)$ and $\mathrm{\Lambda }(1670)$ are generated. The $\mathrm{\Sigma }(1385)$ contribution is included by means of a free parameter, the only one of the theory, up to a global normalization, when one considers only external emission, and we observe that the spin flip part of this term, usually ignored in theoretical and experimental works, plays an important role determining the shape of the mass distributions. Internal emission is also considered and it is found to play a minor role.

This paper explores how magnetic fields affect the Casimir effect within the context of a simple quasi-1D interacting fermionic system. A novel phenomenon emerges, resulting from the interaction between external magnetic fields and boundary conditions, which alters the ground state in complex ways and leads to first-order phase transitions among various ground states, specifically inhomogeneous solutions with differing node counts. We calculate the Casimir force, which exhibits discontinuities (jumps) at the transition points between the different ground states.

Generalizing from previous work on the integer quantum Hall effect, we construct the effective action for the analog of Laughlin states for the fractional quantum Hall effect in higher dimensions. The formalism is a generalization of the parton picture used in two spatial dimensions, the crucial ingredient being the cancellation of anomalies for the gauge fields binding the partons together. Some subtleties which exist even in two dimensions are pointed out. The effective action is obtained from a combination of the Dolbeault and Dirac index theorems. We also present expressions for some transport coefficients such as Hall conductivity and Hall viscosity for the fractional states.

For quantum mechanical anharmonic oscillator-type Hamiltonians, it is shown that there is a relation between the energy eigenvalues of parity symmetric and $\mathcal{PT}$-symmetric phases for weak coupling. The possibility of such a relation was conjectured by Ai, Bender, and Sarkar on examining the imaginary part of the ground state energy using path integrals. In the weak coupling limit, we show that the conjecture is true also for the real part of the ground state energy and of the excited state energies. However, the conjecture is false for strong coupling. The analogous relation for partition functions in zero spacetime dimensions is valid for many cases. However $O(N)$ symmetric multicomponent scalar fields, with $N>1$ and a quartic interaction, do not satisfy the conjecture for zero and one dimensional spacetime. The possibility that the conjecture is valid, for a single component field theory in higher dimensional spacetimes, is discussed in a simplified model.

While the orbital eccentricity is a key feature of the gravitational two-body problem, providing an unambiguous definition in general relativity poses significant challenges. Despite such foundational issue, the eccentricity of binary black holes has important implications in gravitational-wave astronomy. We present a novel approach to consistently define the orbital eccentricity in general relativity, grounded in the mathematical field of catastrophe theory. Specifically, we identify the presence of catastrophes, i.e., breakdowns of the stationary-phase approximation, in numerical relativity waveforms and exploit them to develop a robust and fully gauge-invariant estimator of the eccentricity. Our procedure does not require orbital fitting and naturally satisfies the Newtonian limit. The proposed eccentricity estimator agrees with and generalizes a previous proposal, though with a fully independent derivation. We extract gauge-free eccentricity estimates from about 100 numerical relativity simulations and find that the resulting values are systematically lower compared to those reported alongside the simulations themselves.