In [Phys. Rev. D 80, 123003 (2009)] Schmidt suggested that dynamical dark energy (DDE) propagating on the phantom brane could mimick $\mathrm{\Lambda }\mathrm{CDM}$. Schmidt went on to derive a phenomenological expression for ${\rho }_{\mathrm{DE}}$ which could achieve this. We demonstrate that while Schmidt’s central premise is correct, the expression for ${\rho }_{\mathrm{DE}}$ derived by [Schmidt, Phys. Rev. D 80, 123003 (2009)] is flawed. We derive the correct expression for ${\rho }_{\mathrm{DE}}$ which leads to $\mathrm{\Lambda }\mathrm{CDM}$-like expansion on the phantom brane. We also show that DDE on the brane can be associated with a quintessence field and derive a closed form expression for its potential $V(\varphi )$. Interestingly the $\alpha$-attractor based potential $V(\varphi )\propto {\coth }^2\lambda \varphi$ makes braneworld expansion resemble $\mathrm{\Lambda }\mathrm{CDM}$. However the two models can easily be distinguished on the basis of density perturbations which grow at different rates on the braneworld and in $\mathrm{\Lambda }\mathrm{CDM}$.

A cosmological model with a specific form of the Hubble parameter is constructed in a flat homogeneous, and isotropic background in the framework of $f(R,T)$ gravity, where $R$ is the scalar curvature and $T$ is the trace of the stress-energy-momentum tensor. The proposed functional form of the Hubble parameter is taken in such a way that it fulfills the successful bouncing criteria to find the solution of the gravitational field equations provided the Universe is free from initial singularity. The various constraints on the parameters are involved in the functional form of the Hubble parameter which are analyzed in detail. In addition, we explore physical and geometrical consequences of the model based on the imposed constraints. Furthermore, we demonstrate the bouncing scenario which is realized in our model with some particular values of the model parameters. As a result, we find that all of the necessary conditions are satisfied for a successful bouncing model.

We study the formation of primordial black holes (PBHs) in the early Universe during a period of slow reheating after inflation. We demonstrate how the PBH formation mechanism may change even before the end of the matter-dominated phase and calculate the expected PBH mass function. We find that there is a threshold for the variance of the density contrast, ${\sigma }_c\simeq 0.05$, below which the transition occurs even before reheating, with this having important consequences for the PBH mass function. We also show that there is a maximum cutoff for the PBH mass at around $100M_{\odot }$, below which the subdominant radiation bath affects PBH production, making the scenario particularly interesting for the recent LIGO observations of black hole mergers.

We present an improved method for the precise reconstruction of cosmic-ray air showers above $10^{17}\mathrm{eV}$ with sparse radio arrays. The method is based on the comparison of measured pulses to predictions for radio pulse shapes by CoREAS simulations. We applied our method to the data of Tunka-Rex, a $1{\mathrm{km}}^2$ radio array in Siberia operating in the frequency band of 30–80 MHz. Tunka-Rex is triggered by the air-Cherenkov detector Tunka-133 and by scintillators (Tunka-Grande). The instrument collects air-shower data since 2012. The present paper describes an updated data analysis of Tunka-Rex and details of the new method applied. After quality cuts, when Tunka-Rex reaches its full efficiency, the energy resolution of about 10% given by the new method has reached the limit of systematic uncertainties due to the calibration uncertainty and shower-to-shower fluctuations. At the same time the shower maximum reconstruction has improved compared to the previous method based on the slope of the lateral distribution and reaches a precision of better than $35\mathrm{g}/{\mathrm{cm}}^2$. We also define conditions of the measurements at which the shower maximum resolution of Tunka-Rex reaches a value of $25\mathrm{g}/{\mathrm{cm}}^2$ and becomes competitive to optical detectors. To check and validate our reconstruction and efficiency cuts we compare individual events to the reconstruction of Tunka-133. Furthermore, we compare the mean of the shower maximum as a function of primary energy to the measurements of other experiments.

A tensorial representation of ${\varphi }^4$ field theory introduced by Herbut and Janssen [Phys. Rev. D 93, 085005 (2016)] is studied close to six dimensions, with an eye towards a possible realization of an interacting conformal field theory in five dimensions. We employ the two-loop $\epsilon$ expansion, two-loop fixed-dimension renormalization group, and nonperturbative functional renormalization group. An interacting, real, infrared-stable fixed point is found near six dimensions, and the corresponding anomalous dimensions are computed to the second order in the small parameter $\epsilon =6-d$. Two-loop epsilon expansion indicates, however, that the second-order corrections may destabilize the fixed point at some critical ${\epsilon }_c<1$. A more detailed analysis within all three computational schemes suggests that the interacting, infrared-stable fixed point found previously collides with another fixed point and becomes complex when the dimension is lowered from six towards five. Such a result would conform to the expectation of the triviality of $O(2)$ field theories above four dimensions.

We show how the hopping parameter expansion at order ${\kappa }^2$ and ${\kappa }^4$ can be exploited in the simulation of lattice QCD with two flavors of degenerate Wilson fermions. A natural extension of this idea is a “UV filtering” by using rooted polynomials. These approaches can be easily combined with, for example, mass preconditioning. First numerical tests are performed for the Wilson gauge action at $\beta =5.6$ and $\kappa =0.156$ and 0.1575.

We investigate the leading twist light-cone distribution amplitudes (LCDAs) of vector meson in the framework of large momentum effective theory. We derive the matching equation for the LCDAs and quasidistribution amplitudes. The matching coefficients are determined to one loop accuracy, both in the ultraviolet cutoff and dimensional regularization schemes. This calculation provides the possibility of studying the full $x$ behavior of LCDAs and extracting LCDAs of vector mesons from lattice simulations.

Recent work has established a method of constructing nonsupersymmetric string models that are stable, with near-vanishing one-loop dilaton tadpoles and cosmological constants. This opens up the tantalizing possibility of realizing stable string models whose low-energy limits directly resemble the Standard Model rather than one of its supersymmetric extensions. In this paper we consider the general structure of such strings and find that they share two important phenomenological properties. The first is a so-called “GUT-precursor” structure in which new GUT-like states appear with masses that can be many orders of magnitude lighter than the scale of gauge coupling unification. These states allow a parametrically large compactification volume, even in weakly coupled heterotic strings, and in certain regions of parameter space can give rise to dramatic collider signatures which serve as “smoking guns” for this overall string framework. The second is a residual “entwined-SUSY” (or $e$-SUSY) structure for the matter multiplets in which different multiplet components carry different horizontal $U(1)$ charges. As a concrete example and existence proof of these features, we present a heterotic string model that contains the fundamental building blocks of the Standard Model such as the Standard-Model gauge group, complete chiral generations, and Higgs fields—all without supersymmetry. Even though massless gravitinos and gauginos are absent from the spectrum, we confirm that this model has an exponentially suppressed one-loop dilaton tadpole and displays both the GUT-precursor and $e$-SUSY structures. We also discuss some general phenomenological properties of $e$-SUSY, such as cancellations in radiative corrections to scalar masses, the possible existence of a corresponding approximate moduli space, and the prevention of rapid proton decay.

The quantum null energy condition (QNEC) is a new local energy condition that a general quantum field theory (QFT) is believed to satisfy, relating the classical null energy condition (NEC) to the second functional derivative of the entanglement entropy in the corresponding null direction. We present the first series of explicit computations of QNEC in a strongly coupled QFT, using holography. We consider the vacuum, thermal equilibrium, a homogeneous far-from-equilibrium quench as well as a colliding system that violates NEC. For the vacuum and thermal phase, QNEC is always weaker than NEC. While for the homogeneous quench QNEC is satisfied with a finite gap, we find the interesting result that the colliding system can saturate QNEC, depending on the null direction.

Detections of gravitational waves (GW) in the frequency band 35 to 500 Hz have led to the birth of GW astronomy. Expected signals above 500 Hz, such as the quasinormal modes of lower mass black holes and neutron star merger signatures, are currently not detectable due to increasing quantum shot noise at high frequencies. Squeezed vacuum injection has been shown to allow broadband sensitivity improvement, but this technique does not change the slope of the noise at high frequency. It has been shown that white light signal recycling using negative dispersion optomechanical filter cavities with strong optical dilution for thermal noise suppression can in principle allow broadband high frequency sensitivity improvement. Here we present detailed modeling of AlGaAs/GaAs optomechanical filters to identify the available parameter space in which such filters can achieve the low thermal noise required to allow useful sensitivity improvement at high frequency. Material losses, the resolved sideband condition and internal acoustic modes dictate the need for resonators substantially smaller than previously suggested. We identify suitable resonator dimensions and show that a $30\mu \mathrm{m}$ scale cat-flap resonator combined with optical squeezing allows 8 fold improvement of strain sensitivity at 2 kHz compared with Advanced LIGO. This corresponds to a detection volume increase of a factor of 500 for sources in this frequency range.

Trilinear $Z$ boson interactions are sensitive probes both of new sources of $CP$ violation in physics beyond the standard model and of new particle thresholds. Measurements of trilinear $Z$ interactions are typically interpreted in the frameworks of anomalous couplings and effective field theory, both of which require care in interpretation. To obtain a quantitative picture of the power of these measurements when interpreted in a TeV-scale context, we investigate the anatomy of $ZZZ$ interactions and consider two minimal and perturbative simplified models which induce such interactions through new scalar and fermion loops at the weak scale, focusing on $ZZ$ and vector boson fusion-induced $Zjj$ production at the LHC and $ZZ$ production at a future $e^{+}{e}^{-}$ collider. We show that both threshold and non-threshold effects often are small compared to the sensitivity of the LHC, while the increased sensitivity of a future lepton collider should allow us to constrain such scenarios through associated electroweak precision effects complementary to direct searches at hadron colliders.

Primordial black holes are considered to be pair created quantum-mechanically during inflation. In the context of general relativity (GR), it has been shown that the pair creation rate is exponentially decreasing during inflation. Specifically, tiny black holes are favored in the early universe, but they can grow with the horizon scale, as inflation approaches its end. At the same time, cosmological, and not only, shortcomings of GR have triggered the pursuit for a new, alternative theory of gravity. In this paper, by using probability amplitudes from the no boundary proposal (NBP), we argue that any alternative gravity should have a black hole creation rate similar to that of GR; that is, in the early universe the creation of small black holes is in favor, while in the late universe larger black holes are being exponentially suppressed. As an example, we apply this argument in $f(R)$-theories of gravity and derive a general formula for the rate in any $f(R)$-theory with constant curvature. Finally, we consider well known $f(R)$-models and using this formula we put constraints on their free parameters.

The Gaia mission offers a new opportunity to search for the low-frequency gravitational wave background using astrometric measurements. In this paper, the astrometric effect of gravitational waves is reviewed, with a particular focus on the effect of non-Einsteinian gravitational wave polarizations. A stochastic gravitational wave background generates a correlated vector field of astrometric deflections on the sky. A convenient decomposition for the correlation matrix is introduced, enabling it to be calculated for all possible gravitational wave polarizations and compared to the redshift correlations from the pulsar-timing literature; in the case of a general relativity background of transverse traceless gravitational waves, this also allows us to identify an astrometric analog of the famous Hellings-Downs curve. Finally, the cross correlation between the redshift and astrometric signal is also calculated; this may form the basis for future joint pulsar-timing and astrometry searches for arbitrarily polarized gravitational wave backgrounds.

The precise measurements of cosmic microwave background (CMB) anisotropy angular power spectra made by the Planck satellite show an anomalous value for the lensing amplitude, defined by the parameter $A_{\mathrm{lens}}$, at about 2 standard deviations (2.6 standard deviations when cosmic shear data are included). Moreover, considering $A_{\mathrm{lens}}$ brings the values of the cosmological parameters determined by Planck in better agreement with those found by pre-Planck data sets. In this paper, after discussing the current status of the anomaly, we quantify the potential of future CMB measurements in confirming/falsifying the $A_{\mathrm{lens}}$ tension. We find that a space-based experiment such as LiteBIRD could falsify the current $A_{\mathrm{lens}}$ tension at the level of 5 standard deviations. Similar constraints can be achieved by a stage-III experiment assuming an external prior on the reionization optical depth of $\tau =0.055\pm 0.010$ as already provided by the Planck satellite. A stage-IV experiment could further test the $A_{\mathrm{lens}}$ tension at the level of 10 standard deviations. A comparison between temperature and polarization measurements made at different frequencies could further identify possible systematics responsible for $A_{\mathrm{lens}}>1$. We show that, in the case of the CMB-S4 experiment, polarization data alone have the potential of falsifying the current $A_{\mathrm{lens}}$ anomaly at more than 5 standard deviations and to strongly bound its frequency dependence. We also evaluate the future constraints on a possible scale dependence for $A_{\mathrm{lens}}$.

In models of inflation obtained from string compactification, moduli vacuum misalignment leads to an epoch in the postinflationary history of the Universe when the energy density is dominated by cold moduli particles. This effect leads to a modification in the number of $e$-foldings ($N_{\text{pivot}}$) between the horizon exit of the CMB modes and the end of inflation. Taking Kähler moduli inflation as a prototype, the shift in $e$-foldings turns out to be a function of the model parameters which also determines the inflationary observables. We analyze this scenario numerically using publicly available ModeChord and CosmoMC with the latest Planck+BICEP2/Keck array data to constrain the model parameters and $N_{\text{pivot}}$. In light of the present and future precision data, the results show the importance of the careful consideration of any postinflationary nonstandard epoch, as well as the effects of reheating.

Whether or not the primordial gravitational wave (GW) produced during inflation is sufficiently strong to be observable, GWs are necessarily produced from the primordial curvature perturbations in the second order of perturbation. The induced GWs can be enhanced by curvature perturbations enhanced at small scales or by the presence of matter-dominated stages of the cosmological history. We analytically calculate the integral in the expression of the power spectrum of the induced GWs, which is a universal part independent of the spectrum of the primordial curvature perturbations. This makes the subsequent numerical integrals significantly easy. In simple cases, we derive fully analytic formulas for the induced GW spectrum.

We present the first analytic scheme-independent series calculations of anomalous dimensions of several types of baryon operators at an infrared fixed point (IRFP) in an asymptotically free SU(3) gauge theory with $N_f$ fermions. Separately, for an asymptotically free gauge theory with a gauge group $G$ and $N_f$ fermions in a representation $R$ of $G$, we consider physical quantities at an IRFP, including the anomalous dimension of gauge-invariant fermion bilinears and the derivative of the beta function. These quantities have been calculated in series expansions whose coefficients have been proved to be scheme-independent at each order. We illustrate the scheme independence using a variety of schemes, including the ${\mathrm{RI}}^{\prime }$ scheme and several types of momentum subtraction schemes.

Recently advocated expressions for the phase-space dependent spin-$\frac{1}{2}$ density matrices of particles and antiparticles are analyzed in detail and reduced to forms linear in the Dirac spin operator. This allows for a natural determination of the spin-polarization vectors of particles and antiparticles by evaluating the trace of products of the spin density matrices and the Pauli matrices. We demonstrate that the total spin-polarization vector obtained in this way agrees with the Pauli-Lubański four-vector, constructed from an appropriately chosen spin tensor and boosted to the particle rest frame. We further show that several forms of the spin tensor used in the literature yield the same Pauli-Lubański four-vector.