Ultrahigh-energy (UHE) neutrinos, with EeV-scale energies, carry with them unique insight into fundamental open questions in astrophysics and particle physics. For 50 years, they have evaded discovery, but maybe not for much longer, thanks to new UHE neutrino telescopes, presently under development. We capitalize on this upcoming opportunity by producing state-of-the-art forecasts of the discovery of a diffuse flux of UHE neutrinos in the next 10–20 years. By design, our forecasts are anchored in often-overlooked nuance from theory and experiment; we gear them to the radio array of the planned IceCube-Gen2 detector. We find encouraging prospects: even under conservative analysis choices, most benchmark UHE neutrino flux models from the literature may be discovered within 10 years of detector exposure—many sooner—and may be distinguished from each other. Our results validate the transformative potential of next-generation UHE neutrino telescopes.

Gravitational waves offer a new window to probe the nature of gravity, including answering if the mediating particle, graviton, has a nonzero mass or not. Pulsar timing arrays measure stochastic gravitational wave background (SGWB) at $\sim 1–100\mathrm{nanohertz}$. Recently, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration reported an uncorrelated common-spectrum process in their 12.5-year dataset with no substantial evidence that the process comes from the SGWB predicted by general relativity. In this work, we explore the possibility of an SGWB from massive gravity in the dataset and find that a massless graviton is preferred because of the relatively larger Bayes factor. Without statistically significant evidence for dispersion-related correlations predicted by massive gravity, we place upper limits on the amplitude of the SGWB for graviton mass smaller than ${10}^{-23}\mathrm{eV}$ as $A_{\mathrm{MG}}<3.21\times {10}^{-15}$ at 95% confidence level.

Discrete wavelet-based methods promise to emerge as an excellent framework for the non-perturbative analysis of quantum field theories. In this work, we investigate aspects of renormalization in theories analyzed using wavelet-based methods. We demonstrate the nonperturbative approach of regularization, renormalization, and the emergence of flowing coupling constant within the context of these methods. This is tested on a model of the particle in an attractive Dirac delta function potential in two spatial dimensions, which is known to demonstrate quintessential features found in a typical relativistic quantum field theory.

Scattering amplitudes involving massive spin-2 particles typically grow rapidly with energy. In this paper we demonstrate that the anomalous high-energy growth of the scattering amplitudes cancel for the massive spin-2 Kaluza-Klein modes arising from compactified five-dimensional gravity in a stabilized warped geometry. Generalizing previous work, we show that the two sum rules which enforce the cancellations between the contributions to the scattering amplitudes coming from the exchange of the (massive) radion and those from the exchange of the tower of Goldberger-Wise scalar states (admixtures of the original gravitational and scalar fields of the theory) still persist in the case of the warping which would be required to produce the hierarchy between the weak and Planck scales in a Randall-Sundrum model. We provide an analytic proof of one combination of these generalized scalar sum rules and show how the sum rule depends on the Einstein equations determining the background geometry and the mode-equations and normalization of the tower of physical scalar states. Finally, we provide a consistent and self-contained derivation of the equations governing the physical scalar modes, and we list, in appendixes, the full set of sum rules ensuring proper high-energy growth of all $2\to 2$ massive spin-2 scattering amplitudes.

In this paper, we consider the possibility of generating the observed baryon asymmetry of the Universe via leptogenesis in the context of a triplet fermion-mediated type-III seesaw model of neutrino mass. With a hierarchical spectrum of the additional fermions, the lower bound on the lightest triplet mass is $\sim {10}^{10}\mathrm{GeV}$ for successful leptogenesis, a couple of orders higher than that of the type-I case. We investigate the possibility of lowering this bound in the framework of two-Higgs-doublet models. We find that the bounds can be lowered down to ${10}^7\mathrm{GeV}$ for a hierarchical spectrum. If we include the flavor effects, then a further lowering by one order of magnitude is possible. We also discuss if such lowering can be compatible with the naturalness bounds on the triplet mass.

As a result of the helicity suppression effect, within the Standard Model the rare decay channel $B_s\to e^{+}{e}^{-}$ has a decay probability that is five orders of magnitude below current experimental limits. Thus, any observation of this channel within the current or forthcoming experiments will give unambiguous evidence of physics beyond the Standard Model. In this work, we present for the first time a new physics scenario in which the branching fraction $\overline{\mathcal{B}}r(B_s\to e^{+}{e}^{-})$ is enhanced up to values which saturate the current experimental bounds. More concretely, we study the general two-Higgs-doublet model with a pseudoscalar coupling to electrons unsuppressed by the electron mass. Furthermore, we demonstrate how this scenario can arise from a UV-complete theory of quark-lepton unification that can live at a low scale. This latter step allows us to establish correlations between $B_s\to e^{+}{e}^{-}$ and the lepton-flavor-violating decays ${\tau }^{-}\to {\mu }^{-}{e}^{+}{e}^{-}$ and $\tau \to \mu \gamma$.

We investigate the structure of confining and deconfining phases in SU(2) lattice gauge theory via persistent homology, which gives us access to the topology of a hierarchy of combinatorial objects constructed from given data. Specifically, we use filtrations by traced Polyakov loops, topological densities, holonomy Lie algebra fields, as well as electric and magnetic fields. This allows for a comprehensive picture of confinement. In particular, topological densities form spatial lumps which show signatures of the classical probability distribution of instanton-dyons. Signatures of well-separated dyons located at random positions are encoded in holonomy Lie algebra fields, following the semiclassical temperature dependence of the instanton appearance probability. Debye screening discriminating between electric and magnetic fields is visible in persistent homology and pronounced at large gauge coupling. All employed constructions are gauge-invariant without a priori assumptions on the configurations under study. This work showcases the versatility of persistent homology for statistical and quantum physics studies, barely explored to date.

We study higher-order QCD corrections for the associated production of a top-antitop quark pair and a photon ($t\overline{t}\gamma$ production) in proton-proton collisions. We calculate the approximate next-to-next-to-leading order cross section, with second-order soft-gluon corrections added to the complete next-to-leading order result, including uncertainties from scale dependence and from parton distributions. We compare our results to recent measurements from the LHC, and find that the soft-gluon corrections provide improved agreement with the data. We also calculate differential distributions in top-quark transverse momentum and rapidity.

We calculate the form factors of the ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c(2625)$ and ${\mathrm{\Xi }}_b\to {\mathrm{\Xi }}_c(2815)$ transitions, and additionally evaluate the corresponding semileptonic decays and the color-allowed two-body nonleptonic decays. In order to obtain the concerned form factors, we use the three-body light-front quark model with the support from baryon spectroscopy. In this work, as important physical inputs, the spatial wave functions of concerned baryons are obtained by the Gaussian expansion method with a semirelativistic potential model. For the semileptonic processes, the branching ratios of the electron and muon channels can reach up to the order of magnitude of 1%, where our result $\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}(2625){\mu }^{-}{\nu }_{\mu })=(1.641\pm 0.113)\%$ is consistent with the current experimental data. As for the nonleptonic processes, the decays to ${\pi }^{-}$, ${\rho }^{-}$, and $D_s^{(*)-}$ final states have considerable widths. These discussed decay modes could be accessible at the LHCb experiment.

We study the heavy quark symmetry with the homogeneous bag model (HBM) and light-front quark model (LFQM) based on the decays of ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\ell }^{-}{\overline{\nu }}_{\ell }(\ell =e,\mu ,\tau )$. In particular, we calculate various parameters in the heavy quark expansions, including the Isgur-Wise functions and their first order corrections. The parameters in the HBM are fitted from the mass spectra, while the ones in the LFQM are tightly constrained by the heavy quark symmetry, granting the predictive power of our results. We explicitly obtain that $\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{e}^{-}{\overline{\nu }}_e)=(5.69\pm 0.58,5.35\pm 0.50)$, $\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\mu }^{-}{\overline{\nu }}_{\mu })=(5.67\pm 0.58,5.33\pm 0.49)$, and $\mathrm{\Gamma }({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\tau }^{-}{\overline{\nu }}_{\tau })/\mathrm{\Gamma }({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\mu }^{-}{\overline{\nu }}_{\mu })=(0.3243\pm 0.0126,0.3506\pm 0.0046)$ for the numerical values of (HBM, LFQM). Our results of the branching fractions in both models agree well with the experimental data and lattice QCD calculations. In addition, we find that the hard gluon corrections decrease the branching fractions around 10%.

We present the first search for the Majoron-emitting modes of the neutrinoless double $\beta$ decay ($0\nu \beta \beta {\chi }_0$) using scintillating cryogenic calorimeters. We analyzed the CUPID-0 Phase I data using a Bayesian approach to reconstruct the background sources activities, and evaluate the potential contribution of the ${}^{82}\mathrm{Se}$ $0\nu \beta \beta {\chi }_0$. We considered several possible theoretical models which predict the existence of a Majoron-like boson coupling to the neutrino. The energy spectra arising from the emission of such bosons in the neutrinoless double $\beta$ decay have spectral indices $n=1$, 2, 3, or 7. We found no evidence of any of these decay modes, setting a lower limit (90% of credibility interval) on the half-life of $1.2\times {10}^{23}\mathrm{yr}$ in the case of $n=1$, $3.8\times {10}^{22}\mathrm{yr}$ for $n=2$, $1.4\times {10}^{22}\mathrm{yr}$ for $n=3$ and $2.2\times {10}^{21}\mathrm{yr}$ for $n=7$. These are the best limits on the $0\nu \beta \beta {\chi }_0$ half-life of the ${}^{82}\mathrm{Se}$, and demonstrate the potentiality of the CUPID-0 technology in this field.

We determine the pressure of a cold and dense electron gas to a nearly complete next-to-next-to-next-to-leading order (${\mathrm{N}}^3\mathrm{LO}$) in the fine-structure constant ${\alpha }_e$, utilizing a new result for the two-loop photon self-energy from a companion paper. Our result contains all infrared-sensitive contributions to the pressure at this order, including the coefficient of the $O({\alpha }_e^3\ln {\alpha }_e)$ term, and leaves only a single coefficient associated with the contributions of unresummed hard momenta undetermined. Moreover, we explicitly demonstrate the complete cancellation of infrared divergences according to the effective-field-theory paradigm by determining part of the hard contributions at this order. Our calculation provides the first improvement to a 45-year-old milestone result and demonstrates the feasibility of the corresponding ${\mathrm{N}}^3\mathrm{LO}$ calculation for cold and dense quark matter.

T-duality has been shown to constrain the higher-derivative corrections of string theory. We revisit the problem of understanding the T-duality constraints imposed on the ${\alpha }^{\prime }$ corrections using the language of a torsionful connection. We find a convenient way to express the $O(d,d)$ invariants in terms of linear combinations of the metric and B-field for general $d$-dimensional torus compactifications, which we then use to revisit the heterotic and bosonic ten-dimensional string action at order ${\alpha }^{\prime }$. We also comment on the four-point functions for corrections of order ${\alpha }^{\prime 3}$ in the type II string.

Detecting gravitational waves from coalescing compact binaries allows us to explore the dynamical, nonlinear regime of general relativity and constrain modifications to it. Some of the gravitational-wave events observed by the LIGO-Virgo Collaboration have sufficiently high signal-to-noise ratio in the merger, allowing us to probe the relaxation of the remnant black hole to its final, stationary state—the so-called black-hole ringdown, which is characterized by a set of quasinormal modes. Can we use the ringdown to constrain deviations from general relativity, as predicted by several of its contenders? Here, we address this question by using an inspiral-merger-ringdown waveform model in the effective-one-body formalism, augmented with a parametrization of the ringdown based on an expansion in the final black hole’s spin. We give a prescription on how to include in this waveform model, the quasinormal mode frequencies calculated on a theory-by-theory basis. In particular, we focus on theories that modify general relativity by higher-order curvature corrections, namely, Einstein-dilaton-Gauss-Bonnet, dynamical Chern-Simons theories, and cubic- and quartic-order effective-field-theories of general relativity. We use this parametrized waveform model to measure the ringdown properties of the two loudest ringdown signals observed so far, GW150914 and GW200129. We find that while the Einstein-dilaton-Gauss-Bonnet theory cannot be constrained with these events, we can place upper bounds on the fundamental lengthscale of cubic- (${\ell }_{\text{cEFT}}\le 38.2\mathrm{km}$) and quartic-order (${\ell }_{\text{qEFT}}\le 51.3\mathrm{km}$) effective-field-theories of general relativity, and of dynamical Chern-Simons gravity (${\ell }_{\text{dCS}}\le 38.7\mathrm{km}$). The latter result is a concrete example of a theory presently unconstrained by inspiral-only analyses which, however, can be constrained by merger-ringdown studies with current gravitational-wave data.

Flavor transition mechanisms of supernova (SN) neutrinos during their propagation deserve a close scrutiny. We present a method to verify Mikheyev-Smirnov-Wolfenstein (MSW) effect during the propagation of SN neutrinos from the SN core to the Earth. The non-MSW scenarios to be distinguished from the MSW one are the incoherent flavor transition probability for neutrino propagation in the vacuum and the flavor equalization induced by fast flavor conversions. Our approach involves studying the time evolution of neutrino event rates in liquid argon, liquid scintillation, and water Cherenkov detectors. The liquid argon detector is sensitive to ${\nu }_e$ flux while liquid scintillation and water Cherenkov detectors can measure ${\overline{\nu }}_e$ flux through inverse $\beta$ decay process. The flux of ${\nu }_e$ (${\overline{\nu }}_e$) is a linear combination of ${\nu }_e$ (${\overline{\nu }}_e$) and ${\nu }_{\mu ,\tau }$ (${\overline{\nu }}_{\mu ,\tau }$) fluxes from the source with the weighting of each component dictated by the flavor transition mechanism. Using currently available simulations for SN neutrino emissions, the time evolution of ${\nu }_e\text{Ar}$ and ${\overline{\nu }}_e$ inverse $\beta$ decay event rates and the corresponding cumulative event fractions are calculated up to $t=100\mathrm{ms}$ in DUNE, JUNO, and Hyper-Kamiokande detectors, respectively. It is shown that the area under the cumulative time distribution curve from $t=0$ to $t=100\mathrm{ms}$ in each detector and their ratio can be used to discriminate different flavor transition scenarios of SN neutrinos.

In the context of false vacuum decay at zero temperature, it is well known that bubbles expand with uniform proper acceleration. We show that this uniformly accelerating expansion suffers from an instability related to the bubble size. This can be observed in Minkowski spacetime as a tachyonic mode in the spectrum of fluctuations for the energy functional in the reference frame in which the uniformly accelerating bubble wall appears static. In such a frame, arbitrary small perturbations cause an amplifying departure from the static wall solution. This implies that the nucleated bubble is not a critical point of the energy functional in the rest frame of nucleation but becomes one in the accelerating frame. The aforementioned instability for vacuum bubbles can be related to the well-known instability for the nucleated critical static bubbles during finite-temperature phase transitions in the rest frame of the plasma. It is therefore proposed that zero-temperature vacuum decays as seen from accelerating frames have a dual description in terms of finite-temperature phase transitions.

Observing physical effects of large quantum stress tensor fluctuations requires knowledge of the interactions between the probe and the particles of the underlying quantum fields. The quantum stress tensor operators must first be averaged in time alone or space and time to confer meaningful results, the details of which may correspond to the physical measurement process. We build on prior results to characterize the particle frequencies associated with quantum fluctuations of different magnitudes. For the square of time derivatives of the massless scalar field in a spherical cavity, we find that these frequencies are bounded above in a power law behavior. Our findings provide a way to identify the largest quantum fluctuation that may be probed in experiments relying on frequency-dependent interactions.

We present the first complete calculation of the soft photon self-energy to the next-to-leading order in a hot and/or dense ultrarelativistic plasma in QED. The calculation is performed within the real-time formalism utilizing dimensional regularization in $4-2ϵ$ dimensions, while the result is reported including explicit $O(ϵ)$ terms in the zero-temperature limit. This information is required to extend the perturbative calculation of the pressure of cold and dense QED matter to partial next-to-next-to-next-to-leading order in a weak-coupling expansion, reported in a companion paper. These results pave the way for a similar future calculation in quantum chromodynamics.

Gauge fields provide the fundamental interactions in the Standard Model of particle physics. Gauge field configurations with nontrivial topological windings are known to play crucial roles in many important phenomena, from matter-antimatter asymmetry of today’s universe to spontaneous chiral symmetry breaking in strong interaction. Their presence is, however, elusive for direct detection in experiments. Here we show that measurements of the chiral magnetic effect (CME) in heavy ion collisions can be used for accessing the topological fluctuations of the non-Abelian gauge fields in the quantum chromodynamics (QCD). To achieve this, we implemented a key ingredient, the stochastic dynamics of gauge field topological fluctuations, into a state-of-the-art framework for simulating the CME in these collisions. This new framework provides the necessary tool to quantify initial topological fluctuations from any definitive CME signal to be extracted from experimental data. It also reveals a universal scaling relation between initial topological fluctuations and particle multiplicity produced in the corresponding collision events.