The renormalon singularities are a known source of the divergent behavior of asymptotic perturbative series from field theoretical models. These singularities live in the Borel plane and are responsible for ambiguities in the physical plane. We propose that field theories can have renormalons beyond the usual first Borel plane. We show an example with a scalar field theory where, considering a chain of cat’s eyes diagrams, the model develops a Gevrey-3 asymptotic series.

We describe the dynamical mass generation in pseudoquantum electrodynamics (PQED) coupled to the Gross-Neveu (GN) interaction, in ($2+1$) dimensions, at both zero and finite temperatures. We start with a gapless model and show that, under particular conditions, a dynamically generated mass emerges. In order to do so, we use a truncated Schwinger-Dyson equation, at the large-$N$ approximation, in the imaginary-time formalism. In the instantaneous-exchange approximation (the static regime), we obtain two critical parameters, namely, the critical number of fermions $N_c(T)$ and the critical coupling constant ${\alpha }_c(T)$ as a function of temperature and of the finite cutoff $\mathrm{\Lambda }$, which must be provided by experiments. In the dynamical regime, we find an analytical solution for the mass function $\mathrm{\Sigma }(p,T)$ as well as a zero-external momentum solution for $p=0$. In the continuum theory $\mathrm{\Lambda }=\infty$, where scale-invariance is respected, it is shown that the model has a dynamically generated mass for any value of the coupling constant $\alpha$. Furthermore, after calculating the effective potential for PQED, we prove that the dynamically generated mass is an energetically favorable solution in comparison to the massless phase. We compare our analytical results with numerical tests and a good agreement is found.

A well-recognized open conceptual problem in relativistic quantum field theory concerns the relation between measurement and causality. Naive generalizations of quantum measurement rules can allow for superluminal signaling (“impossible measurements”). This raises the problem of delineating physically allowed quantum measurements and operations. We analyze this issue in a recently proposed framework in which local measurements (in possibly curved spacetime) are described physically by coupling the system to a probe. We show that the state-update rule in this setting is consistent with causality provided that the coupling between the system and probe is local. Thus, by establishing a well-defined framework for successive measurements, we also provide a class of physically allowed operations. Conversely, impossible measurements can only be performed using impossible (nonlocal) apparatus.

We present a detailed methodology for extracting the full set of Newman-Penrose Weyl scalars from numerically generated spacetimes without requiring a tetrad that is completely orthonormal or perfectly aligned to the principal null directions. We also describe how to implement an extrapolation technique for computing the Weyl scalars’ contribution at asymptotic null infinity in postprocessing. These methods have been used to produce ${\mathrm{\Psi }}_4$ and $h$ waveforms for the Simulating eXtreme Spacetimes (SXS) waveform catalog and now have been expanded to produce the entire set of Weyl scalars. These new waveform quantities are critical for the future of gravitational wave astronomy in order to understand the finite-amplitude gauge differences that can occur in numerical waveforms. We also present a new analysis of the accuracy of waveforms produced by the Spectral Einstein Code. While ultimately we expect Cauchy characteristic extraction to yield more accurate waveforms, the extraction techniques described here are far easier to implement and have already proven to be a viable way to produce production-level waveforms that can meet the demands of current gravitational-wave detectors.

Gravitational-wave (GW) observations by a network of ground-based laser interferometric detectors allow us to probe the nature of GW polarizations. This would be an interesting test of general relativity, since general relativity predicts only two polarization modes while there are theories of gravity that predict up to six polarization modes. The ability of GW observations to probe the nature of polarizations is limited by the available number of linearly independent detectors in the network. (To extract all polarization modes, there should be at least as many detectors as the polarization modes.) Strong gravitational lensing of GWs offers a possibility to significantly increase the effective number of detectors in the network. Due to strong lensing (e.g., by galaxies), multiple copies of the same signal can be observed with time delays of several minutes to weeks. Owing to the rotation of the earth, observation of the multiple copies of the same GW signal would allow the network to measure different combinations of the same polarizations. This effectively multiplies the number of detectors in the network. Focusing on strongly lensed signals from binary black hole mergers that produce two observable “images,” using Bayesian model selection and assuming simple polarization models, we show that our ability to distinguish between polarization models is significantly improved.

We carry on a comprehensive study on static fluid distributions endowed with hyperbolical symmetry. Their physical properties are analyzed in detail. The energy density appears to be necessarily negative, which suggests that any possible application of this kind of fluids requires extreme physical conditions where quantum effects are expected to play an important role. Also, it is found that the fluid distribution cannot fill the region close to the center of symmetry. Such a region may be represented by a vacuum cavity around the center. A suitable definition of mass function, as well as the Tolman mass are explicitly calculated. While the former is positive defined, the latter is negative in most cases, revealing the repulsive nature of gravitational interaction. A general approach to obtain exact solutions is presented and some exact analytical solutions are exhibited.

Observation of gravitational waves (GWs) in two different frequency bands is referred to as multiband GW astronomy. With the planned Laser Interferometric Space Antenna (LISA) operating in the ${10}^{-4}–0.1\mathrm{Hz}$ range, and third-generation (3G) ground-based detectors such as the Cosmic Explorer (CE) and Einstein Telescope (ET) operating in the $1–{10}^4\mathrm{Hz}$ range, multiband GW astronomy could be a reality in the coming decades. In this paper, we present the potential of multiband observations of intermediate-mass binary black holes (IMBBHs) of component masses $\sim {10}^2–{10}^3{M}_{\odot }$ to test general relativity (GR). We show that mutiband observations of IMBBHs would permit multiparameter tests of GR—tests where more than one post-Newtonian (PN) coefficient is simultaneously measured—yielding more rigorous constraints on possible modifications to GR. We also find that the improvement due to multibanding can often be much larger than the best of the bounds from either of the two observatories. The origin of this result, as we shall demonstrate, can be traced to the lifting of degeneracies among the various parameters when the information from LISA and 3G is taken together. A binary of redshifted total mass of $200M_{\odot }$ gives the best bounds. Such a system at 1 Gpc and mass ratio $m_1/m_2=2$ would bound the deviations on all the PN coefficients to below 10% when they are measured individually, and additionally place simultaneous bounds on the first seven PN coefficients to below 50%.

Scalar-tensor theories of gravity are known to allow significant deviations from general relativity through various astrophysical phenomena. In this paper, we formulate a scalar-connection gravity by setting up scalars and connection configurations instead of metric. Since the matter sector is not straightforward to conceive without a metric, we invoke cosmological fluids in terms of their one-form velocity in the volume element of the invariant action. This leads to gravitational equations with a perfect fluid source and a generated metric, which are expected to produce reasonable deviations from general relativity in the strong field regime. As a relevant application, we study a spontaneous scalarization mechanism and show that the Damour-Esposito-Farèse model arises in a certain class of scalar-connection gravity. Furthermore, we investigate a general study in which the present framework becomes distinguishable from the famed scalar-tensor theories.

We consider the possibility that the dark sector of our Universe contains a negative cosmological constant dubbed $\lambda$. For such models to be viable, the dark sector should contain an additional component responsible for the late-time accelerated expansion rate ($X$). We explore the departure of the expansion history of these models from the concordance$\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model. For a large class of our models, the accelerated expansion is transient with a nontrivial dependence on the model parameters. All models with $w_X>-1$ will eventually contract and we derive an analytical expression for the scale factor $a(t)$ in the neighborhood of its maximal value. We find also the scale factor for models ending in a Big Rip in the regime where dustlike matter density is negligible compared to $\lambda$. We address further the viability of such models, in particular when a high $H_0$ is taken into account. While we find no decisive evidence for a nonzero $\lambda$, the best models are obtained with a phantom behavior on redshifts $z\gtrsim 1$ with a higher evidence for nonzero $\lambda$. An observed value for $h$ substantially higher than 0.70 would be a decisive test of their viability.

We study the cosmological consequences of a class of Dirac-Born-Infeld models, and assess their viability as a candidate for the recent acceleration of the Universe. The model includes both the rolling tachyon field and the generalized Chaplygin gas models as particular limits, and phenomenologically each of these provides a possible mechanism for a deviation of the value of the dark energy equation of state from its canonical (cosmological constant) value. The field-dependent potential that is characteristic of the rolling tachyon also leads to variations of the fine-structure constant $\alpha$, implying that the model can be constrained both by standard cosmological probes and by astrophysical measurements of $\alpha$. Our analysis, using the latest available low-redshfit data and local constraints from atomic clock and weak equivalence principle experiments, shows that the two possible deviations of the dark energy equation of state are constrained to be ${\log }_{10}(1+w_0{)}_V<-7.85$ and ${\log }_{10}(1+w_0{)}_C<-0.85$, respectively for the rolling tachyon and Chaplygin components, both being at the 95.4% confidence level (although the latter depends on the choice of priors, in a way that we quantify). Alternatively, the 95.4% confidence level bound on the dimensionless slope of the potential is ${\log }_{10}\lambda <-5.36$. This confirms previous analyses indicating that in these models the potential needs to be extremely flat.

Modern simulation codes for general relativistic ideal magnetohydrodynamics are all facing a long-standing technical problem given by the need to recover fundamental variables from those variables that are evolved in time. In the relativistic case, this requires the numerical solution of a system of nonlinear equations. Although several approaches are available, none has proven completely reliable. A recent study comparing different methods showed that all can fail, in particular for the important case of strong magnetization and moderate Lorentz factors. Here, we propose a new robust, efficient, and accurate solution scheme, along with a proof for the existence and uniqueness of a solution, and analytic bounds for the accuracy. Further, the scheme allows us to reliably detect evolution errors leading to unphysical states and automatically applies corrections for typical harmless cases. A reference implementation of the method is made publicly available as a software library. The aim of this library is to improve the reliability of binary neutron star merger simulations, in particular in the investigation of jet formation and magnetically driven winds.

Self-interacting dark matter (SIDM) has gathered growing attention as a solution to the small-scale problems of the collisionless cold dark matter (CDM). We investigate the SIDM using stellar kinematics of the 23 ultra-faint dwarf (UFD) galaxies with the phenomenological SIDM halo model. The UFDs are DM-dominated and have less active star formation history. Therefore, they are the ideal objects to test the SIDM, as their halo profiles are hardly affected by the baryonic processes. We found no UFDs favor nonzero self-interaction and some provide stringent constraints. Our result challenges the simple halo modeling of the SIDM, which urges further investigation of the subhalo dynamical evolution of the SIDM.

In this paper, we review and update the Amaral-Gay Ducati-Betemps-Soyez saturation model, by testing it against the recent H1-ZEUS combined data on deep inelastic scattering, including heavy quarks in the dipole amplitude. We obtain that this model, which is based on traveling wave solutions of the Balitsky-Kovchegov equation and built in the momentum space framework, yields very accurate descriptions of the reduced cross section, ${\sigma }_r(x,y,Q^2)$, as well as DIS structure functions such as $F_2(x,Q^2)$ and $F_L(x,Q^2)$, all measured at HERA. Additionally, it provides good descriptions of heavy quark structure functions, $F_2^{cc}$ and $F_2^{bb}$ at small-$x$ and $Q^2\lesssim 60{\mathrm{GeV}}^2$. We also use the improved model to make predictions for structure functions to be measured in the near future at LHeC.

We study the effect of boundary conditions on vacuum polarization for charged scalar fields in two space-time dimensions. We find that both Dirichlet and Neumann boundary conditions lead to screening. In the Dirichlet case, the vacuum polarization charge density vanishes at the boundary, whereas it attains its maximum there for Neumann boundary conditions. At a critical field strength, the vacuum polarization diverges for Neumann boundary conditions, an effect due to the instability of the lowest energy mode in the presence of the external field.

We introduce a three-Higgs doublet model (3HDM) with two inert (or dark) scalar doublets and an active Higgs one, hence termed $\mathrm{I}(2+1)\mathrm{HDM}$, in the presence of a discrete $Z_3$ symmetry acting upon the three doublet fields. We show that such a construct yields a dark matter (DM) sector with two mass-degenerate states of opposite $CP$ quantum number, both of which contribute to DM dynamics, which we call “hermaphrodite DM,” distinguishable from a (single) complex DM candidate. We show that the relic density contributions of both states are equal, saturating the observed relic density compliant with (in)direct searches for DM as well as other experimental data impinging on both the dark and Higgs sectors of the model, chiefly, in the form of electroweak precision observables, Standard Model-like Higgs boson measurements at the Large Hadron Collider and void searches for additional (pseudo)scalar states at the CERN machine and previous colliders.

We report an analytical and numerical investigation into the impact of helicity inversion in LHC processes that do not conserve lepton number ($L$). As a case study, we focus on the production and decay of Majorana neutrinos ($N$) through on- and off-shell $W$ bosons in the phenomenological type I seesaw model. Using the Monte Carlo event generator madgraph5_amc@nlo in conjunction with the heavyn model libraries, we perform exact matrix element (ME) computations without the narrow width approximation. Despite helicity inversion appearing explicitly in MEs, we report the absence of helicity suppression of $L$-violating collider observables for $1\to 4$ and $2\to 4$ processes that are dominated by resonant $N$ production. We attribute this incongruity to the different scalings of 4-momenta and squared 4-momenta in MEs and squared MEs, with exact cancelations occurring in the latter when $N$ goes on-shell in the small-width limit. In off-shell regimes, total suppression/enhancement of $L$ violation can emerge. Implications for other neutrino mass models are discussed.

Using a low-energy effective field theory approach, we study some properties of models with large extra dimensions, in which quarks and leptons have localized wave functions in the extra dimensions. We consider models with two types of gauge groups: (i) the Standard-Model gauge group, and (ii) the left-right symmetric gauge group. Our main focus is on the lepton sector of models with $n=2$ extra dimensions, in particular, neutrino masses and mixing. We analyze the requisite conditions that the models must satisfy to be in accord with data and present a solution for lepton wave functions in the extra dimensions that fulfils these conditions. As part of our work, we also present a new solution for quark wave function centers. Issues with flavor-changing neutral-current effects are assessed. Finally, we remark on baryogenesis and dark matter in these models.

We study the predictions for $CP$ phases and absolute neutrino mass scale for broad classes of models with a U(2)-like flavor symmetry. For this purpose we consider the same special textures in neutrino and charged lepton mass matrices that are successful in the quark sector. While in the neutrino sector the U(2) structure enforces two texture zeros, the contribution of the charged lepton sector to the Pontecorvo-Maki–Nakagawa–Sakata (PMNS) matrix can be parametrized by two rotation angles. Restricting to the cases where at least one of these angles is small, we obtain three representative scenarios. In all scenarios we obtain a narrow prediction for the sum of neutrino masses in the range of 60–75 meV, possibly in the reach of upcoming galaxy survey experiments. All scenarios can be excluded if near-future experimental date provide evidence for either neutrinoless double-beta decay or inverted neutrino mass ordering.

We investigate the interaction between a heavy quark-antiquark pair in color octet configuration in a gluon plasma. We calculate nonperturbatively the effective thermal potential for hybrid states with static $Q\overline{Q}$ octet and an adjoint gluonic source. We compare the results for two different gluonic sources, which lead to completely different potentials in the confined phase. We find that they show identical thermal potentials to large distances, and interpret this potential as the interaction potential between the static $Q$ and the $\overline{Q}$ in a color octet configuration. We present results for the potential in gluon plasma for moderately high temperatures $\lesssim 2T_c$. The implications of our result are discussed.