We consider inflationary models with a Gauss-Bonnet term to reconstruct the scalar-field potentials and the Gauss-Bonnet coupling functions. Both expressions are derived from the observationally favored configurations of $n_s$ and $r$. Our result implies that, for the reconstructed potentials and coupling functions, the blue tilt of inflationary tensor fluctuations can be realized. To achieve a blue tilt for the inflationary tensor fluctuations, a scalar field must climb up its potential before rolling down. We further investigate the properties of propagation of the perturbation modes in Friedmann-Robertson-Walker spacetime. For the reconstructed configurations that give rise to the blue tilt for the inflationary tensor fluctuations, we show that the ghosts and instabilities are absent with the superluminal propagation speeds for the scalar perturbation modes, whereas the propagation speeds of the tensor perturbations are subluminal.

Galaxy surveys probe both structure formation and the expansion rate, making them promising avenues for understanding the dark universe. Photometric surveys accurately map the 2D distribution of galaxy positions and shapes in a given redshift range, while spectroscopic surveys provide sparser 3D maps of the galaxy distribution. We present a way to analyse overlapping 2D and 3D maps jointly and without loss of information. We represent 3D maps using spherical Fourier-Bessel (sFB) modes, which preserve radial coverage while accounting for the spherical sky geometry, and we decompose 2D maps in a spherical harmonic basis. In these bases, a simple expression exists for the cross-correlation of the two fields. One very powerful application is the ability to simultaneously constrain the redshift distribution of the photometric sample, the sample biases, and cosmological parameters. We use our framework to show that combined analysis of DESI and LSST can improve cosmological constraints by factors of $\sim 1.2$ to $\sim 1.8$ on the region where they overlap relative to identically sized disjoint regions. We also show that in the overlap of DES and SDSS-III in Stripe 82, cross-correlating improves photo-$z$ parameter constraints by factors of $\sim 2$ to $\sim 12$ over internal photo-$z$ reconstructions.

Future galaxy surveys promise to probe local primordial non-Gaussianity at unprecedented precision, $\sigma (f_{\mathrm{NL}})\lesssim 1$. We study the implications for multifield inflation by considering spectator models, where inflation is driven by the inflaton field, but the primordial perturbations are (partially) generated by a second, spectator field. We perform a Markov chain Monte Carlo likelihood analysis using Planck data to study quantitative predictions for $f_{\mathrm{NL}}$ and other observables for a range of such spectator models. We show that models where the primordial perturbations are dominated by the spectator field, while fine-tuned within the broader parameter space, typically predict $f_{\mathrm{NL}}$ of order unity. Therefore, upcoming galaxy clustering measurements will constitute a stringent test of whether or not the generation of primordial perturbations and the accelerated expansion in the inflationary universe are due to separate phenomena.

In this paper, I construct a class of everywhere regular geometric sigma models that possess bouncing solutions. Precisely, I show that every bouncing metric can be made a solution of such a model. My previous attempt to do so by employing one scalar field has failed due to the appearance of harmful singularities near the bounce. In this work, I use four scalar fields to construct a class of geometric sigma models which are free of singularities. The models within the class are parametrized by their background geometries. I prove that, whatever background is chosen, the dynamics of its small perturbations is classically stable on the whole time axis. Contrary to what one expects from the structure of the initial Lagrangian, the physics of background fluctuations is found to carry two tensor, two vector, and two scalar degrees of freedom. The graviton mass, which naturally appears in these models, is shown to be several orders of magnitude smaller than its experimental bound. I provide three simple examples to demonstrate how this is done in practice. In particular, I show that graviton mass can be made arbitrarily small.

We compute the net electric current generated during a first order electroweak phase transition when fermions transit from the false to the true vacuum. This current is generated by the charge parity conjugation ($CP$)-violating fermion interaction with the Higgs field during the phase transition and is quantified in terms of a $CP$-violating phase in the bubble wall separating the symmetric from the symmetry-broken phases. We comment on the seed magnetic field that this current is able to generate, and it is possible implications for magnetogenesis in the early Universe during the electroweak phase transition.

Employing a simplified version of the Israel-Stewart formalism of general-relativistic shear-viscous hydrodynamics, we explore the evolution of a remnant massive neutron star of binary neutron star merger and pay special attention to the resulting gravitational waveforms. We find that for the plausible values of the so-called viscous alpha parameter of the order ${10}^{-2}$ the degree of the differential rotation in the remnant massive neutron star is significantly reduced in the viscous time scale, $\lesssim 5\mathrm{ms}$. Associated with this, the degree of nonaxisymmetric deformation is also reduced quickly, and as a consequence, the amplitude of quasiperiodic gravitational waves emitted also decays in the viscous time scale. Our results indicate that for modeling the evolution of the merger remnants of binary neutron stars we would have to take into account magnetohydrodynamics effects, which in nature could provide the viscous effects.

Van der Waals interactions between two neutral but polarizable systems at a separation $R$ much larger than the typical size of the systems are at the core of a broad sweep of contemporary problems in settings ranging from atomic, molecular and condensed matter physics to strong interactions and gravity. In this paper, we reexamine the dispersive van der Waals interactions between two hydrogen atoms. The novelty of the analysis resides in the usage of nonrelativistic effective field theories of quantum electrodynamics. In this framework, the van der Waals potential acquires the meaning of a matching coefficient in an effective field theory, dubbed van der Waals effective field theory, suited to describe the low-energy dynamics of an atom pair. It may be computed systematically as a series in $R$ times some typical atomic scale and in the fine-structure constant $\alpha$. The van der Waals potential gets short-range contributions and radiative corrections, which we compute in dimensional regularization and renormalize here for the first time. Results are given in $d$ space-time dimensions. One can distinguish among different regimes depending on the relative size between $1/R$ and the typical atomic bound-state energy, which is of order $m{\alpha }^2$. Each regime is characterized by a specific hierarchy of scales and a corresponding tower of effective field theories. The short-distance regime is characterized by $1/R\gg m{\alpha }^2$ and the leading-order van der Waals potential is the London potential. We also compute next-to-next-to-next-to-leading-order corrections. In the long-distance regime we have $1/R\ll m{\alpha }^2$. In this regime, the van der Waals potential contains contact terms, which are parametrically larger than the Casimir-Polder potential that describes the potential at large distances. In the effective field theory, the Casimir-Polder potential counts as a next-to-next-to-next-to-leading-order effect. In the intermediate-distance regime, $1/R\sim m{\alpha }^2$, a significantly more complex potential is obtained. We compare this exact result with the two previous limiting cases. We conclude by commenting on the van der Waals interactions in the hadronic case.

There is no guarantee that the violation of the lepton number, assuming it exists, will primarily manifest itself in neutrinoless double beta decay ($0\nu \beta \beta$). Lepton-number violation and lepton-flavor violation may be related, and much-needed information regarding the physics that violates the lepton number can be learned by exploring observables that violate lepton flavors other than the electron flavor. One of the most promising observables is the ${\mu }^{-}\to e^{+}$ conversion, which can be explored by experiments that are specifically designed to search for the ${\mu }^{-}\to e^{-}$ conversion. We survey lepton-number violating dimension-five, -seven, and -nine effective operators in the standard model and discuss the relationships between Majorana neutrino masses and the rates for $0\nu \beta \beta$ and the ${\mu }^{-}\to e^{+}$ conversion. While $0\nu \beta \beta$ has the greatest sensitivity to new ultraviolet energy scales, its rate might be suppressed by the new physics relationship to lepton flavor, and the ${\mu }^{-}\to e^{+}$ conversion offers a complementary probe of lepton-number-violating physics.

We investigate the ability of the upcoming Hyper-Kamiokande (Hyper-K) neutrino experiment to detect new physics phenomena beyond the standard, three-massive-neutrinos paradigm; namely, the existence of a fourth, sterile neutrino or weaker-than-weak, nonstandard neutrino interactions. With both beam-based neutrinos from the Japan Proton Accelerator Research Complex (J-PARC) and atmospheric neutrinos, Hyper-K is capable of exploring new ranges of parameter space in these new-physics scenarios. We find that Hyper-K has comparable capability to the upcoming Deep Underground Neutrino Experiment (DUNE), and that combining both beam- and atmospheric-based data can clear up degeneracies in the parameter spaces of interest. We also comment on the potential improvement in searches for new physics if a combined analysis were performed using Hyper-K and DUNE data.

The measured $\overline{B}\to D^{(*)}l\overline{\nu }$ decay rates for light leptons ($l=e$, $\mu$) constrain all $\overline{B}\to D^{(*)}$ semileptonic form factors, by including both the leading and $\mathcal{O}({\mathrm{\Lambda }}_{\mathrm{QCD}}/m_{c,b})$ subleading Isgur-Wise functions in the heavy quark effective theory. We perform a novel combined fit to the $\overline{B}\to D^{(*)}l\overline{\nu }$ decay distributions to predict the $\overline{B}\to D^{(*)}\tau \overline{\nu }$ rates and determine the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$. Most theoretical and experimental papers have neglected uncertainties in the predictions for form factor ratios at order ${\mathrm{\Lambda }}_{\mathrm{QCD}}/m_{c,b}$, which we include. We also calculate $\mathcal{O}({\mathrm{\Lambda }}_{\mathrm{QCD}}/m_{c,b})$ and $\mathcal{O}({\alpha }_s)$ contributions to semileptonic $\overline{B}\to D^{(*)}\ell \overline{\nu }$ decays for all possible $b\to c$ currents. This result has not been available for the tensor current form factors, and for two of those, which are $\mathcal{O}({\mathrm{\Lambda }}_{\mathrm{QCD}}/m_{c,b})$, the corrections are of the same order as approximations used in the literature. These results allow us to determine with improved precision how new physics may affect the $\overline{B}\to D^{(*)}\tau \overline{\nu }$ rates. Our predictions can be systematically improved with more data; they need not rely on lattice QCD results, although these can be incorporated.

We provide comprehensive investigations for the mass spectrum of exotic open-flavor charmed/bottom $sq\overline{q}\overline{c}$, $qq\overline{q}\overline{c}$, $sq\overline{q}\overline{b}$, $qq\overline{q}\overline{b}$ tetraquark states with various spin-parity assignments $J^P=0^{+},1^{+},2^{+}$ and $0^{-}$, $1^{-}$ in the framework of QCD sum rules. In the diquark configuration, we construct the diquark-antidiquark interpolating tetraquark currents using the color-antisymmetric scalar and axial-vector diquark fields. The stable mass sum rules are established in reasonable parameter working ranges, which are used to give reliable mass predictions for these tetraquark states. We obtain the mass spectra for the open-flavor charmed/bottom $sq\overline{q}\overline{c}$, $qq\overline{q}\overline{c}$, $sq\overline{q}\overline{b}$, $qq\overline{q}\overline{b}$ tetraquark states with various spin-parity quantum numbers. In addition, we suggest searching for exotic doubly-charged tetraquarks, such as $[sd][\overline{u}\overline{c}]\to D_s^{(*)-}{\pi }^{-}$ in future experiments at facilities such as BESIII, BelleII, PANDA, LHCb, and CMS, etc.

In recent years, there have appeared in the literature a large number of static, spherically symmetric metrics, which are regular at the origin, asymptotically flat, and have both an event and a Cauchy horizon for a certain range of the parameters. They have been interpreted as regular black hole (BH) spacetimes, and their physical source attributed to electric or magnetic monopoles in a suitable chosen nonlinear electrodynamics. Here we show that these metrics can also be interpreted as exact solutions of the Einstein equations coupled to ordinary linear electromagnetism—i.e., as sources of the Reissner-Nordström (RN) spacetime—provided the components of the effective energy-momentum tensor satisfy the dominant energy condition (DEC). We use some well-known regular BH metrics to construct nonsingular RN black holes, where the singularity at the RN center is replaced by a regular perfect fluid charged sphere (whose charge-to-mass ratio is not greater than 1) which is inside the RN inner horizon.

Models of loop quantum gravity based on real connections have a deformed notion of general covariance, which leads to the phenomenon of signature change. This result is confirmed here in a general analysis of all midisuperspace models without local degrees of freedom. As a subclass of models, two-dimensional theories of dilaton gravity appear, but a larger set of examples is possible based only on the condition of anomaly freedom. While the classical dilaton gravity models are the only such systems without deformed covariance, they do give rise to signature change when holonomy modifications are included.

A no-hair theorem for spherical black holes in scalar-tensor gravity is presented. Contrary to the existing theorems, which are proved in the Einstein conformal frame, this proof is performed entirely in the Jordan frame. The theorem is limited to spherical symmetry (instead of axisymmetry) but holds for nonconstant Brans-Dicke couplings.

Holographic cosmology offers a novel framework for describing the very early Universe in which cosmological predictions are expressed in terms of the observables of a three-dimensional quantum field theory (QFT). This framework includes conventional slow-roll inflation, which is described in terms of a strongly coupled QFT, but it also allows for qualitatively new models for the very early Universe, where the dual QFT may be weakly coupled. The new models describe a universe which is nongeometric at early times. While standard slow-roll inflation leads to a (near-) power-law primordial power spectrum, perturbative super-renormalizable QFTs yield a new holographic spectral shape. Here, we compare the two predictions against cosmological observations. We use CosmoMC to determine the best fit parameters, and MultiNest for Bayesian evidence, comparing the likelihoods. We find that the dual QFT should be nonperturbative at the very low multipoles ($l\lesssim 30$), while for higher multipoles ($l\gtrsim 30$) the new holographic model, based on perturbative QFT, fits the data just as well as the standard power-law spectrum assumed in $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. This finding opens the door to applications of nonperturbative QFT techniques, such as lattice simulations, to observational cosmology on gigaparsec scales and beyond.

We construct a model in which the cosmological constant is canceled from the gravitational equations of motion. Our model relies on two key ingredients: a nonlocal constraint on the action, which forces the spacetime average of the Lagrangian density to vanish, and a dynamical way for this condition to be satisfied classically with arbitrary matter content. We implement the former condition with a spatially constant Lagrange multiplier associated with the volume form and the latter by including a free four-form gauge field strength in the action. These two features are enough to remove the cosmological constant from the Einstein equation. The model is consistent with all cosmological and experimental bounds on modification of gravity and allows for both cosmic inflation and the present epoch of acceleration.

We use NuSTAR observations of the Galactic center to search for x-ray lines from the radiative decay of sterile neutrino dark matter. Finding no evidence of unknown lines, we set limits on the sterile neutrino mass and mixing angle. In most of the mass range 10–50 keV, these are now the strongest limits, at some masses improving upon previous limits by a factor of $\sim 10$. In the $\nu \mathrm{MSM}$ framework, where additional constraints from dark matter production and structure formation apply, the allowed parameter space is reduced by more than half. Future NuSTAR observations may be able to cover much of the remaining parameter space.

We propose that the flavor structure of the standard model is based on a horizontal $SU(2)$ symmetry. It generically predicts (i) a parametrically small mass for the lightest charged fermions, (ii) small mixings in the quark sector, and (iii) suppression of flavor-changing neutral currents. Supplemented with the assumption of a strong hierarchy between the second- and third-generation masses, it also predicts (iv) a large $CP$-violating phase in the quark sector. Only Majorana neutrinos allow for large mixings in the lepton sector. In this case, this framework further predicts (v) near-maximal ${\theta }_{23}^l$, (vi) a normal hierarchy of neutrino masses, and (vii) large $CP$ violation in the lepton sector.

Adding an extra singlet scalar $S$ to the Higgs sector can provide a barrier at tree level between a false vacuum with restored electroweak symmetry and the true one. This has been demonstrated to readily give a strong phase transition as required for electroweak baryogenesis. We show that with the addition of a fermionic dark matter particle $\chi$ coupling to $S$, a simple UV-complete model can realize successful electroweak baryogenesis. The dark matter gets a $CP$ asymmetry that is transferred to the standard model through a $CP$ portal interaction, which we take to be a coupling of $\chi$ to $\tau$ leptons and an inert Higgs doublet. The $CP$ asymmetry induced in left-handed $\tau$ leptons biases sphalerons to produce the baryon asymmetry. The model has promising discovery potential at the LHC, while robustly providing a large enough baryon asymmetry and correct dark matter relic density with reasonable values of the couplings.

We calculate two- and three-body decays of the (lightest) vector glueball into (pseudo)scalar, (axial-)vector, as well as pseudovector and excited vector mesons in the framework of a model of QCD. While absolute values of widths cannot be predicted because the corresponding coupling constants are unknown, some interesting branching ratios can be evaluated by setting the mass of the yet hypothetical vector glueball to 3.8 GeV as predicted by quenched lattice QCD. We find that the decay mode $\omega \pi \pi$ should be one of the largest (both through the decay chain $\mathcal{O}\to b_1\pi \to \omega \pi \pi$ and through the direct coupling $\mathcal{O}\to \omega \pi \pi$). Similarly, the (direct and indirect) decay into $\pi K{K}^{*}(892)$ is sizable. Moreover, the decays into $\rho \pi$ and $K^{*}(892)K$ are, although subleading, possible and could play a role in explaining the $\rho \pi$ puzzle of the charmonium state $\psi (2S)$ thanks to a (small) mixing with the vector glueball. The vector glueball can be directly formed at the ongoing BESIII experiment as well as at the future PANDA experiment at the FAIR facility. If the width is sufficiently small ($\lesssim 100\mathrm{MeV}$) it should not escape future detection. It should be stressed that the employed model is based on some inputs and simplifying assumptions: the value of glueball mass (at present, the quenched lattice value is used), the lack of mixing of the glueball with other quarkonium states, and the use of few interaction terms. It then represents a first step toward the identification of the main decay channels of the vector glueball, but shall be improved when corresponding experimental candidates and/or new lattice results will be available.