The test masses in next-generation gravitational-wave interferometers may have a semiconductor substrate, most likely silicon. The stochastic motion of charge carriers within the semiconductor will cause random fluctuations in the material’s index of refraction, introducing a noise source called thermal charge carrier refractive (TCCR) noise. TCCR noise was previously studied in 2020 by Bruns et al., using a Langevin force approach. Here we compute the power spectral density of TCCR noise by both using the fluctuation-dissipation theorem and accounting for previously neglected effects of the standing wave of laser light produced by reflections along the direction of beam propagation. We quantify our results with parameters from Einstein Telescope, and we show that at temperatures of 10 K the amplitude of TCCR noise is up to a factor of $\sqrt{2}$ times greater than what was previously claimed. From 77 K to 300 K the amplitude is around 5 to 7 orders of magnitude lower than previously claimed when we choose to neglect the standing wave, and is up to a factor of 6 times lower if the standing wave is included. Despite these differences, we still conclude like Bruns et al. that TCCR noise should not be a limiting noise source for next-generation gravitational-wave interferometers.

We consider the possibility that dark matter (DM) only interacts with the Standard Model leptons, but not quarks at tree level, and analyze the future lepton collider prospects of such leptophilic DM in the mono-photon and mono-$Z$ (both leptonic and hadronic) channels. Adopting a model-independent effective field theory framework, we consider all possible dimension-six operators of scalar-pseudoscalar (SP), vector-axial vector (VA), and tensor-axial tensor (TAT) types for a fermionic DM and derive the collider sensitivities on the effective cutoff scale $\mathrm{\Lambda }$ as a function of the DM mass. As a concrete example, we take the beam configurations of the International Linear Collider with $\sqrt{s}=1\mathrm{TeV}$ and $8{\mathrm{ab}}^{-1}$ integrated luminosity, including the effect of beam polarization, and show that it can probe leptophilic DM at $3\sigma$ level up to $\mathrm{\Lambda }$ values of 6.6, 8.8, and 7.1 TeV for the SP-, VA-, and TAT-type operators, respectively. This is largely complementary to the direct and indirect searches for leptophilic DM and can potentially provide the best-ever sensitivity in the low-mass DM regime.

We discuss baryogenesis in scenarios where the Universe is reheated to temperatures $\lesssim 100\mathrm{GeV}$ by the decay of long-lived massive particles into energetic SM particles. Before its thermalization, the center-of-mass energy in collisions between such a particle and a particle from the ambient plasma can be higher than the typical sphaleron mass, even if the temperature of the plasma itself is much lower. Optimistic estimates for the high energy enhancement of the sphaleron cross section suggest that successful baryogenesis is possible for reheating temperatures as low as 0.1–1 GeV. With a simple extension of the SM, sufficient baryon production should be achieved by enhancing the W-boson coupling even if more pessimistic results for the sphaleron rate are correct. In both cases, if the two to many sphaleron reaction is significant enough for the baryogenesis, the same process can be probed in collider and cosmic-ray experiments. Complementing such experimental tests, a significantly improved understanding of the two to many sphaleron rate in the nonperturbative coupling regime is mandatory to determine whether this scenario is viable. Finally, we briefly discuss the possible origin of the required $CP$ violation.

Tensor network states, and in particular projected entangled pair states (PEPS) have been a strong ansatz for the variational study of complicated quantum many-body systems, thanks to their built-in entanglement entropy area law. In this work, we use a special kind of PEPS—gauged Gaussian fermionic PEPS (GGFPEPS)—to find the ground state of $2+1$ dimensional pure ${\mathbb{Z}}_2$ lattice gauge theories for a wide range of coupling constants. We do so by combining PEPS methods with Monte-Carlo computations, allowing for efficient contraction of the PEPS and computation of correlation functions. Previously, such numerical computations involved the calculation of the Pfaffian of a matrix scaling with the system size, forming a severe bottleneck; in this work we show how to overcome this problem. This paves the way for applying the method we propose and benchmark here to other gauge groups, higher dimensions, and models with fermionic matter, in an efficient, sign-problem-free way.

In this paper we present an improved regularization-independent (RI)-type prescription appropriate for the nonperturbative renormalization of gauge-invariant nonlocal operators. In this prescription, the nonperturbative vertex function is improved by subtracting unwanted finite lattice spacing ($a$) effects, calculated in lattice perturbation theory. The method is versatile and can be applied to a wide range of fermion and gluon actions, as well as types of nonlocal operators. The presence of operator mixing can also be accommodated. Compared to the standard ${\mathrm{RI}}^{\prime }$ prescription, this variant can be recast as a supplementary finite renormalization, whose coefficients bring about corrections of higher order in $a$; consequently, it coincides with standard ${\mathrm{RI}}^{\prime }$ as $a\to 0$—however, it can afford us a smoother and more controlled extrapolation to the continuum limit. In this proof-of-concept calculation we focus on nonlocal fermion bilinear operators containing a straight Wilson line. In the numerical implementation we use Wilson clover fermions and Iwasaki improved gluons. The finite-$a$ terms were calculated to one-loop level in lattice perturbation theory, and to all orders in $a$, using the same action as the nonperturbative vertex functions. We find that the method leads to significant improvement in the perturbative region indicated by small and intermediate values of the length of the Wilson line. This results in a robust extraction of the renormalization functions in that region. We have also applied the above method to operators with stout-smeared links. We show how to perform the perturbative correction for any number of smearing iterations and evaluate its effect on the power divergent renormalization coefficients.

We show that methods developed in the context of perturbative calculations can be transferred to nonperturbative calculations. We demonstrate that correlation functions on the lattice can be computed with the method of differential equations, supplemented with techniques from twisted cohomology. We derive differential equations for the variation with the coupling or—more generally—with the parameters of the action. Already simple examples show that the differential equation with respect to the coupling has an essential singularity at zero coupling and a regular singularity at infinite coupling. The properties of the differential equation at zero coupling can be used to prove that the perturbative series is only an asymptotic series.

We show that the phase structure of certain staggered fermion theories can be understood on the basis of exact anomalies. These anomalies arise when staggered fermions are coupled to gravity which can be accomplished by replacing them by discrete Kähler-Dirac fermions. We first show the existence of a perturbative anomaly in even dimensions which breaks an exact $U(1)$ symmetry of the massless theory down to $Z_4$. If we attempt to gauge this $Z_4$ symmetry we find a ’t Hooft anomaly which can only be canceled for multiples of two Kähler-Dirac fields. This result is consistent with the cancellation of a further mixed nonperturbative ’t Hooft anomaly between the global $Z_4$ and a reflection symmetry. In four-dimensional flat space, theories of two staggered fields yield eight Dirac or 16 Majorana fermions in the continuum limit and this critical number of fermions agrees with results in condensed matter theory literature on the fermion content required to gap boundary fermions in $4+1$-dimensional topological superconductors. It is also consistent with constraints stemming from the cancellation of spin-$Z_4$ anomalies of Weyl fermions. Indeed, cancellation of ’t Hooft anomalies is a necessary requirement for symmetric mass generation and this result gives a theoretical explanation of recent numerical work on the phase diagram of interacting staggered fermions. As an application of these ideas we construct a lattice model whose low-energy continuum limit is conjectured to yield the Pati-Salam grand unified theory.

We study infrared (IR) divergences in light front quantum chromodynamics using a coherent state basis in light front time-ordered Hamiltonian perturbation theory. In computation of the S-matrix elements in Hamiltonian formalism, the IR divergences appear in the form of vanishing energy denominators. We consider the process $e^{+}{e}^{-}\to 2$ jets at $\mathcal{O}(g^2)$ in strong coupling, construct the coherent state representing the outgoing particles, and explicitly show that the “true” IR divergences cancel to this order when the matrix elements are calculated between coherent states instead of Fock states.

In classical Bianchi I spacetimes, underlying conditions for what dictates the singularity structure—whether it is anisotropic shear or energy density, can be easily determined from the generalized Friedmann equation. However, in nonsingular bouncing anisotropic models these insights are difficult to obtain in the quantum gravity regime where the singularity is resolved at a nonvanishing mean volume which can be large compared to the Planck volume, depending on the initial conditions. Such nonsingular models may also lack a generalized Friedmann equation making the task even more difficult. We address this problem in an effective spacetime description of loop quantum cosmology (LQC) where energy density and anisotropic shear are universally bounded due to quantum geometry effects, but a generalized Friedmann equation has been difficult to derive due to the underlying complexity. Performing extensive numerical simulations of effective Hamiltonian dynamics, we bring to light a surprising, seemingly universal relationship between energy density and anisotropic shear at the bounce in LQC. For a variety of initial conditions for a massless scalar field, an inflationary potential, and two types of ekpyrotic potentials we find that the values of energy density and the anisotropic shear at the quantum bounce follow a novel parabolic relationship which reveals some surprising results about the anisotropic nature of the bounce, such as that the maximum value of the anisotropic shear at the bounce is reached when the energy density reaches approximately half of its maximum allowed value. The relationship we find can prove very useful for developing our understanding of the degree of anisotropy of the bounce, isotropization of the postbounce universe, and discovering the modified generalized Friedmann equation in Bianchi I models with quantum gravity corrections.

The long-standing problem of time in canonical quantum gravity is the source of several conceptual and technical issues. Here, recent mathematical results are used to provide a consistent algebraic formulation of dynamical symplectic reduction that avoids difficult requirements such as the computation of a complete set of Dirac observables or the construction of a physical Hilbert space. In addition, the new algebraic treatment makes it possible to implement a consistent realization of the gauge structure off the constraint surface. As a consequence, previously unrecognized consistency conditions are imposed on deparametrization—the method traditionally used to unfreeze evolution in completely constrained systems. A detailed discussion of how the new formulation extends previous semiclassical results shows that an internal time degree of freedom need not be semiclassical in order to define a consistent quantum evolution.

After generalizing the Regge-Teitelboim formulation of gravity to include the case where the background embedding space is not flat, we examine the dynamics of the four-dimensional $k=0$ Robertson-Walker (RW) manifold embedded in various five-dimensional backgrounds. We find that when the background is five-dimensional de Sitter space, the RW manifold undergoes a transition from a deaccelerating phase to an accelerating phase. This occurs before the inclusion of matter, radiation or cosmological constant sources, and thus does not require a balance of different components. We obtain a reasonable two-parameter fit of this model to the Hubble parameter data.

We investigate the cosmological consequences of the modified Friedmann equations when the entropy associated with the apparent horizon, given by Barrow entropy, $S\sim A^{1+\delta /2}$, where $0\le \delta \le 1$ represents the amount of the quantum-gravitational deformation of the horizon. We study implications of this model in a flat Friedmann-Robertson-Walker universe with/without a cosmological constant. Taking the cosmological constant into account, this model can describe the current accelerated expansion, although the transition from deceleration phase to the acceleration phase takes place in the lower redshifts. We investigate the evolution of the scale factor and show that with increasing $\delta$, the value of the scale factor increases as well. We also estimate the age of the universe in Barrow cosmology which is smaller than the age of the universe in standard cosmology.

Extragalactic foregrounds are known to generate significant biases in temperature-based cosmic microwave background (CMB) lensing reconstruction. Several techniques, which include “source hardening” and “shear-only estimators” have been proposed to mitigate contamination and have been shown to be very effective at reducing foreground-induced biases. Here we extend both techniques to polarization, which will be an essential component of CMB lensing reconstruction for future experiments, and investigate the “large-lens” limit analytically to gain insight on the origin and scaling of foreground biases, as well as the sensitivity to their profiles. Using simulations of polarized point sources, we estimate the expected bias to both Simons Observatory and CMB-S4 like (polarization-based) lensing reconstruction, finding that biases to the former are minuscule while those to the latter are potentially non-negligible at small scales ($L\sim 1000–2000$). In particular, we show that for a CMB-S4 like experiment, an optimal linear combination of point-source hardened estimators can reduce the (point-source induced) bias to the CMB lensing power spectrum by up to two orders of magnitude, at a $\sim 4\%$ noise cost relative to the global minimum variance estimator.

The measurement of the inflationary stochastic gravitational wave background (SGWB) is one of the main goals of future GW experiments. In direct GW experiments, an obstacle to achieving it is the isolation of the inflationary SGWB from the other types of SGWB. In this paper, as a distinguishable signature of the inflationary SGWB, we argue the detectability of its universal property: antipodal correlations, i.e., correlations of GWs from the opposite directions, as a consequence of the horizon reentry. A phase-coherent method has been known to be of no use for detecting the angular correlations in SGWB due to a problematic phase factor that erases the signal. We thus investigate whether we can construct a phase-incoherent estimator of the antipodal correlations in the intensity map. We found that the conclusion depends on whether the inflationary GWs have statistical isotropy or not. In the standard inflationary models with statistical homogeneity and isotropy, there is no estimator that is sensitive to the antipodal correlations but does not suffer from the problematic phase factor. On the other hand, it is possible to find a nonvanishing estimator of the antipodal correlations for inflationary models with statistical anisotropy. SGWB from anisotropic inflation is distinguishable from the other components.

There are many single field inflationary models that are consistent with the recent Planck 2018 measurements of the spectral index $n_s$ and tensor-to-scalar ratio $r$. Despite good agreement with observational data some of these models suffer from having unregularized potentials which would produce a collapsing universe shortly after the end of inflation. In this paper we show that how one chooses to correct the behavior potential toward the end of inflation can have a significant effect on the inflationary predictions of the model, specifically in the case of quartic hilltop and radiatively corrected Higgs inflation.

We propose that the nature of indirect signals of dark matter (DM) can depend on the Galactic environment they originate from. We demonstrate this possibility in models where DM annihilates into light mediators whose branching fractions depend on a long-range force sourced by ordinary matter. In particular, electromagnetic signals of DM may only arise near the centers of galaxies where the ordinary matter densities, and hence astrophysical background levels, are high. We briefly discuss how our model could explain the Galactic Center gamma ray excess, without leaving much of a trace in baryon-poor environments, like dwarf spheroidal galaxies. Similar spatial dependence of indirect signals can also apply to models featuring metastable DM decay into light mediators.

Mounting evidence suggests that the launching of collapsar jets is magnetically driven. Recent general relativistic magnetohydrodynamic simulations of collapsars reveal that the jet is continuously loaded with baryons, owing to strong mixing with the cocoon. This results in a high photosphere at $\gtrsim {10}^{12}\mathrm{cm}$. Consequently, collisionless internal shocks below the photosphere are disfavored, and neutrino production in the deepest jet regions is prevented, in contrast to what has been assumed in the literature. We find that subphotospheric neutrino production could take place in the presence of collisionless subshocks or magnetic reconnection. Efficient particle acceleration is not possible in the cocoon, at the cocoon-countercocoon shock interface, or at the shock driven by the cocoon in the event of a jet halted in an extended envelope. These subphotospheric neutrinos have energy $E_{\nu }\lesssim {10}^5\mathrm{GeV}$ for initial jet magnetizations ${\sigma }_0=15–2000$. More than one neutrino event is expected to be observed in Hyper-Kamiokande and IceCube DeepCore for bursts occurring at $z\lesssim \mathcal{O}(0.1)$. Because of their energy, these neutrinos cannot contribute to the diffuse flux detected by the IceCube Neutrino Observatory. Our findings have implications on neutrino searches ranging from gamma-ray bursts to luminous fast blue optical transients.

Crystalline materials are increasingly employed to construct precision optical instruments because of their reduced mechanical dissipation and consequent reduction of thermal Brownian noise. However, the anisotropy of the crystalline state implies a fundamental source of thermal noise; depolarization induced by thermal fluctuations of its birefringence. We establish the theory of this effect, which is a generalization of prior treatments of thermo-optic noises in amorphous materials. This theory—in conjunction with poorly understood anisotropic thermal stress coefficients of crystalline coatings—predict that thermo-refringent noise in crystalline mirror coatings may be lurking within an order of magnitude of Brownian noise (below 100 Hz). Thus, in order to appreciate the full promise of crystalline optical materials, a more precise understanding of their anisotropic material constants is necessary. Barring that, we elucidate measurement techniques that can affect partial coherent cancellation of thermorefringent noise. In passing, our general formalism also predicts the existence of thermal beam-pointing noise.

We present a detailed study on variational autoencoders (VAEs) for anomalous jet tagging at the Large Hadron Collider. By taking in low-level jet constituents’ information and training with background QCD jets in an unsupervised manner, the VAE is able to encode important information for reconstructing jets, while learning an expressive posterior distribution in the latent space. When using the VAE as an anomaly detector, we present different approaches to detect anomalies: directly comparing in the input space or, instead, working in the latent space. A comprehensive series of test sets are generated to fully examine the anomalous tagging performance in different jet types. In order to facilitate general search approaches such as bump hunt, mass-decorrelated VAEs based on distance correlation regularization are also studied. We find that the naive mass-decorrelated VAEs fail at maintaining proper detection performance, by assigning higher probability to some anomalous samples. To build a performant mass-decorrelated anomalous jet tagger, we propose the outlier exposed VAE (OE-VAE), for which some outlier samples are introduced in the training process to guide the learned information. OE-VAEs are employed to achieve two goals at the same time: increasing sensitivity of outlier detection and decorrelating jet mass from the anomaly score. We succeed in reaching excellent results from both aspects.