Beta-spectrum of radioactive atoms was long ago predicted to bear an imprint of the cosmic neutrino background ($\mathrm{C}\nu \mathrm{B}$) [S. Weinberg, Phys. Rev. 128, 1457 (1962)]. Over the years, it has been recognized that the best chance of achieving the signal-to-noise ratio required for the observation of this effect lies with solid-state designs [E. Baracchini et al., arXiv:1808.01892.]. Here we bring to the fore a fundamental quantum limitation on the type of beta-decayer that can be used in a such a design. We derive a simple usability criterion and show that ${}^3\mathrm{H}$, which is the most popular choice, fails to meet it. We provide a list of potentially suitable isotopes and discuss why their use in $\mathrm{C}\nu \mathrm{B}$ detection requires further research.

We show that color-breaking vacua may develop at high temperature in the minisplit supersymmetry (SUSY) scenario. This can lead to a nontrivial cosmological history of the Universe, including strong first order phase transitions and domain wall production. Given the typical PeV energy scale associated with minisplit SUSY models, a stochastic gravitational wave background at frequencies around 1 kHz is expected. We study the potential for detection of such a signal in future gravitational wave experiments.

We introduce the $CP$ violating scalar leptoquark $S_3$ to explain the measured values of the lepton universality ratios $R_{K^{(*)}}$. We derive constraints on the $CP$-even and $CP$-odd components of the leptoquark Yukawa couplings stemming from effects in $b\to s\mu \mu$ and $B_s$ mixing. For the $b\to s\mu \mu$ processes we impose $R_{K^{(*)}}$, $\mathcal{B}(B_s\to {\mu }^{+}{\mu }^{-})$, as well as $CP$-sensitive angular asymmetries $A_{7,8,9}$, whereas in the $B_s$ mixing sector $\mathrm{\Delta }{M}_s$ and $S_{\psi \varphi }$ are considered. Combining the constraints within the $S_3$ model reveals that a large $CP$ phase with a definite sign is perfectly viable for a leptoquark of mass below a few TeV. For larger mass of the $S_3$ leptoquark the $CP$ phase is suppressed due to the observables pertaining to the $B_s$ system. We provide predictions of direct and mixing-induced $CP$ asymmetries in $B\to K\mu \mu$ that could reveal the presence of the novel $CP$ phase.

The tiny neutrino masses can be explained naturally by extending the standard model with right-handed Majorana neutrinos in a low-scale seesaw mechanism, and the $CP$ violation effect induced by the Majorana phase is interesting and worth studying at colliders. In this paper, we investigate the prospects for measuring $CP$ violation in top quark pair production and rare decay via Majorana neutrinos at the LHC. The $CP$ asymmetry stems from the significant interference of contributions from two different Majorana neutrinos and can be appreciable when the two neutrino masses are nearly degenerate. It is found that in the Majorana neutrino mass range of $10\mathrm{GeV}<m_N<80\mathrm{GeV}$, the $CP$ asymmetry is independent of the Majorana neutrino mass at the LHC. Any possible new observation of $CP$ violation will be the clear evidence of new physics beyond the standard model.

We study real-time meson-meson scattering processes in ($1+1$)-dimensional QED by means of tensor networks. We prepare initial meson wave packets with given momentum and position introducing an approximation based on the free fermions model. Then, we compute the dynamics of two initially separated colliding mesons, observing a rich phenomenology as the interaction strength and the initial states are varied in the weak and intermediate coupling regimes. Finally, we consider elastic collisions and measure some scattering amplitudes as well as the entanglement generated by the process. Remarkably, we identify two different regimes for the asymptotic entanglement between the outgoing mesons: it is perturbatively small below a threshold coupling, past which its growth as a function of the coupling abruptly accelerates.

We calculate in the framework of collinear factorization the amplitude for the photoproduction of a near forward large mass diphoton at leading twist and next to leading order (NLO) in ${\alpha }_s$. We demonstrate the validity of factorization at this order, which was never achieved for such a reaction where the coefficient function describes a $2\to 3$ hard process. While the Born order amplitude was purely imaginary and only probed the $x=\pm \xi$ cross-over line of generalized parton distributions (GPD) domain, the NLO result contains both a real and an imaginary part and probes the whole domain of definition of quark GPDs. The phenomenology of our results for medium (JLab) and higher energy (EIC) experiments will be developed in a future study.

The holographic light-front QCD framework provides a unified nonperturbative description of the hadron mass spectrum, form factors and quark distributions. In this article we extend holographic QCD in order to describe the gluonic distribution in both the proton and pion from the coupling of the metric fluctuations induced by the spin-two Pomeron with the energy momentum tensor in anti–de Sitter space, together with constraints imposed by the Veneziano model, without additional free parameters. The gluonic and quark distributions are shown to have significantly different effective QCD scales.

We systematically revisit the baryonic four-body semileptonic decays of $B^{-}\to \mathbf{B}{\overline{\mathbf{B}}}^{\prime }{\ell }^{-}{\overline{\nu }}_{\ell }$ by the perturbative QCD counting rules with $\mathbf{B}$ representing octet baryons and $\ell =e$, $\mu$. We study the transition form factors of $B^{-}\to \mathbf{B}{\overline{\mathbf{B}}}^{\prime }$ in the limit of $(p_{\mathbf{B}}+p_{{\overline{\mathbf{B}}}^{\prime }}{)}^2\to \infty$ with the three-body $\overline{B}\to \mathbf{B}{\overline{\mathbf{B}}}^{\prime }M$ and $B^{-}\to p\overline{p}{\mu }^{-}{\overline{\nu }}_{\mu }$ data along with $SU(3{)}_f$ flavor symmetry. We calculate the decay branching ratios and angular asymmetries as well as the differential decay branching fractions of $B^{-}\to p\overline{p}{\ell }^{-}{\overline{\nu }}_{\ell }$. In particular, we find that our new result of $\mathcal{B}(B^{-}\to p\overline{p}{\ell }^{-}{\overline{\nu }}_{\ell })=(5.21\pm 0.34)\times {10}^{-6}$, which is about one order of magnitude lower than the previous theoretical prediction of $(10.4\pm 2.9)\times {10}^{-5}$, agrees well with both experimental measurements of $(5.8_{-2.3}^{+2.6})\times {10}^{-6}$ and $(5.3\pm 0.4)\times {10}^{-6}$ by the Belle and LHCb Collaborations, respectively. We also evaluate the branching ratios and angular asymmetries in other channels of $B^{-}\to \mathbf{B}\overline{\mathbf{B}}{\ell }^{-}{\overline{\nu }}_{\ell }$, which can be tested by the ongoing experiments at LHCb and Belle-II.

Maggiore observed that, in the high-damping regime, the quasinormal modes spectrum for the Schwarzschild black hole resembles that of a quantum harmonic oscillator. Motivated by this observation, we describe a black hole as a statistical ensemble of $N$ quantum harmonic oscillators. By working in the canonical ensemble, we show that, in the large-mass black hole limit, the leading contribution to the Gibbs entropy is the Bekenstein-Hawking term, while the subleading one is a logarithmic correction, in agreement with several results in the literature. We also find that the number of oscillators scales holographically with the area of the event horizon.

We revisit the entanglement harvesting protocol when two detectors are in causal contact. We study the role of field-mediated communication in generating entanglement between the two detectors interacting with a quantum field. We provide a quantitative estimator of the relative contribution of communication versus genuine entanglement harvesting. For massless scalar fields in flat spacetime, we show that when two detectors can communicate via the field, the detectors do not really harvest entanglement from the field, and instead they get entangled only via the field-mediated communication channel. In other words, in these scenarios the entanglement harvesting protocol is truly “harvesting entanglement” from the field only when the detectors are not able to communicate. In contrast, for massive scalar fields both communication and genuine harvesting contribute equally to the bipartite entanglement when the detectors are causally connected. These results emphasize the importance of taking into account the causal relationships between two parties involved in this relativistic quantum information protocol before we can declare that it is truly entanglement harvesting.

The dressed-state formalisms, which incorporate interactions of soft particles into an asymptotic state, are known as the prescriptions expected to solve the problem of infrared (IR) divergence in the quantum field theory (QFT). A particularly famous example is the dressed-state formalism proposed by Kulish and Faddeev in quantum electrodynamics (QED). As pointed out by Hirai and Sugishita, however, this formalism has problems in gauge invariance and the IR divergence. These problems are mainly caused by the existence of ghosts or unphysical photon modes. Therefore, we start by studying the asymptotic states in the Coulomb gauge, which excludes ghosts and/or unphysical photon modes. In this paper, we propose a formalism to construct the asymptotic states directly from the interaction of the theory by setting a sufficiently large timescale $T$. In this dressed-state formalism, we define the asymptotic interaction remaining at $|t|>T$ in terms of some fixed order of $1/T$, and we are performing all calculations according to that order. We study the asymptotic states in QED specifically, but we can formally apply the dressed-state formalism proposed in this paper to any perturbative QFT. We show that, at least in QED, we can construct a divergence-free and unitary $S$-matrix using dressed states proposed in this paper. Furthermore, we discuss the transition rate to show that we can predict experimental results. We also show that the U(1) gauge symmetry of the $S$-matrix leads to the QED large gauge symmetry, and the deviation of the expectation values of the vector potential between initial and final spacelike hypersurfaces emerges as a QED memory effect. The dressed-state formalism in this paper may give a unified and new insight into IR physics, including asymptotic symmetries, memory effects, and unitarity of the state evolution.

We develop a general formalism of duality rotations for bosonic conformal spin-$s$ gauge fields, with $s\ge 2$, in a conformally flat four-dimensional spacetime. In the $s=1$ case, this formalism is equivalent to the theory of U(1) duality-invariant nonlinear electrodynamics developed by Gaillard and Zumino, Gibbons and Rasheed, and generalized by Ivanov and Zupnik. For each integer spin $s\ge 2$ we demonstrate the existence of families of conformal U(1) duality-invariant models, including a generalization of the so-called ModMax electrodynamics ($s=1$). Our bosonic results are then extended to the $\mathcal{N}=1$ and $\mathcal{N}=2$ supersymmetric cases. We also sketch a formalism of duality rotations for conformal gauge fields of Lorentz type $(m/2,n/2)$, for positive integers $m$ and $n$.

We construct the first analytic examples of nonhomogeneous condensates in the Georgi-Glashow model at finite density in ($2+1$) dimensions. The nonhomogeneous condensates, which live within a cylinder of finite spatial volume, possess a novel topological charge that prevents them from decaying in the trivial vacuum. Also the non-Abelian magnetic flux can be computed explicitly. These solutions exist for constant and nonconstant Higgs profile and, depending on the length of the cylinder, finite density transitions occur. In the case in which the Higgs profile is not constant, the full system of coupled field equations reduce to the Lamé equation for the gauge field (the Higgs field being an elliptic function). For large values of this length, the energetically favored configuration is the one with a constant Higgs profile, while, for small values, is the one with the nonconstant Higgs profile. The non-Abelian Chern-Simons term can also be included without spoiling the integrability properties of these configurations. Finally, we study the stability of the solutions under a particular type of perturbations.

Compact binary systems with black holes are the primary sources of interferometric advanced gravitational wave detectors. Astrophysical models suggest possibility of binary systems with appreciable nonzero eccentricity in the dense stellar environment like globular clusters and galactic nuclei. While most of the compact binary events have not shown appreciable eccentricity, constrains on the eccentricity have been placed on few detected events. With increasing sensitivity of the gravitational wave detectors, the eccentric binaries are plausible sources in the gravitational wave window. Nevertheless, the challenges in the waveform modeling for high values of eccentricity constrain both the search methodologies of eccentric system as well as parameter estimation of the eccentricity. Waveform independent approaches are being investigated. In this work, we demonstrate that a new effective chirp mass ${\mathcal{M}}_e$ parameter can be defined which governs the inspiral dynamics of the nonspinning eccentric compact binary system. We obtain the phenomenological model of the same for low to moderate eccentricity values. One direct implication is its application in the unmodeled searches and as an another implication, we demonstrate that this model can be used to constrain the eccentricity of the nonspinning eccentric binaries in the advanced detector era in the waveform model-independent way.

We consider spatially covariant modified gravity in which the would-be scalar degree of freedom is made nondynamical and hence there are just two tensorial degrees of freedom, i.e., the same number of dynamical degrees of freedom as in general relativity. Focusing on a class of such modified gravity theories characterized by three functions of time, we discuss how modified gravity with two tensorial degrees of freedom can be distinguished observationally or phenomenologically from general relativity. It is checked that the theory gives the same predictions as general relativity for the parametrized post-Newtonian parameter $\gamma$ and the propagation speed of gravitational waves. We also find that there is no modification to asymptotically flat black holes at rest with respect to the preferred frame. Due to a large degree of freedom to choose the time-dependent functions in the theory, the homogeneous and isotropic cosmological dynamics can be made close to or even identical to that of the $\mathrm{\Lambda }\mathrm{CDM}$ model. We investigate the behavior of cosmological perturbations in the long- and short-wavelength limits and show that in both limits the effects of modified gravity appear only through the modification of the background evolution. Finally, it is remarked that in the presence of a Galileon field in the matter sector, the scalar degree of freedom is revived, ruining the essential feature of the theory.

Extreme mass-ratio inspirals (EMRIs) detectable by the Laser Inteferometric Space Antenna (LISA) are unique probes of astrophysics and fundamental physics. Parameter estimation for these sources is challenging, especially because the waveforms are long, complicated, known only numerically, and slow to compute in the most relevant regime, where the dynamics is relativistic. We perform a time-consuming Fisher-matrix error analysis of the EMRI parameters using fully relativistic numerical waveforms to leading order in an adiabatic expansion on a Kerr background, taking into account the motion of the LISA constellation, higher harmonics, and also including the leading correction from the spin of the secondary in the postadiabatic approximation. We pay particular attention to the convergence of the numerical derivatives in the Fisher matrix and to the numerical stability of the covariance matrix, which for some systems requires computing the numerical waveforms with approximately 90-digit precision. Our analysis confirms previous results (obtained with approximated but much more computationally efficient waveforms) for the measurement errors on the binary’s parameters. We also show that the inclusion of higher harmonics improves the errors on the luminosity distance and on the orbital angular momentum angles by one order and two orders of magnitude, respectively, which might be useful to identify the environments where EMRIs live. We particularly focus on the measurability of the spin of the secondary, confirming that, for spin-aligned EMRIs on quasicircular orbits, it cannot be measured with sufficient accuracy. However, due to correlations, its inclusion in the waveform model can deteriorate the accuracy on the measurements of other parameters by orders of magnitude, unless a physically motivated prior on the secondary spin is imposed.

We study the observation of polarized stochastic gravitational-wave background (SGWB) in pulsar-timing-array experiments. The time residual for an observed pulsar is formulated as a line-of-sight integral that incorporates the effects of the pulsar term, from which we construct the correlation function of the time residual between a pair of pulsars in terms of the overlap reduction functions (ORFs) for the SGWB intensity and polarization anisotropies. Our formulation provides a numerical scheme for computing the ORFs for high multipole moments, and the lowest-moment ORFs for the SGWB linear polarization are worked out for the first time.

To ensure that the light (emitted far away from the source of gravity) can arrive at the null infinity of an asymptotically flat spacetime, it is shown that the rate of Bondi mass aspect has to satisfy some conditions. In Einstein gravity theory, we find the sufficient condition implies a bound on the Bondi mass loss, i.e., $|\dot{m}|\le 0.3820c^3/G$. This provides a new perspective on Dyson’s maximum luminosity. However, in Brans-Dicke theory, the sufficient condition depends on the behavior of the radiation field of the scalar. Specifically, the photons can escape to the null infinity when the scalar gravitational radiation is not too large and the mass loss is not too fast.

We investigate gravitational lensing by a photon sphere in a Reissner-Nordström naked singularity spacetime in strong deflection limits. Because of the nonexistence of an event horizon and the existence of a potential barrier near an antiphoton sphere, infinite numbers of images slightly inside and outside of a photon sphere can appear. We obtain the analytic expressions of the factors of logarithmic divergent terms and the constant terms of the deflection angles in the strong deflection limits not only the for the little outside but also the barely inside of the photon sphere without Taylor expansions in the power of an electric charge. We can distinguish between a Reissner-Nordström black hole spacetime and the naked singularity spacetime since the images little inside of the photon sphere around the naked singularity are significantly brighter than the image barely outside of the photon sphere around the black hole and the naked singularity.

Accurate waveform models are crucial for gravitational-wave data analysis, and since spin has a significant effect on the binary dynamics, it is important to improve the spin description in these models. In this paper, we derive the spin-orbit (SO) coupling at the fifth-and-a-half post-Newtonian (5.5PN) order. The method we use splits the conservative dynamics into local and nonlocal-in-time parts, and then relates the local-in-time part to gravitational self-force results by exploiting the simple mass-ratio dependence of the post-Minkowskian expansion of the scattering angle. We calculate the nonlocal contribution to the 5.5PN SO dynamics to eighth order in the small-eccentricity expansion for bound orbits, and to leading order in the large-eccentricity expansion for unbound orbits. For the local contribution, we obtain all of the 5.5PN SO coefficients from first-order self-force results for the redshift and spin-precession invariants, except for one unknown that could be fixed in the future by second-order self-force results. However, by incorporating our 5.5PN results in the effective-one-body formalism and comparing its binding energy to numerical relativity, we find that the remaining unknown has a small effect on the SO dynamics, demonstrating an improvement in accuracy at that order.