We analyze the linear causality and stability of third-order fluid dynamics considering perturbations around a global equilibrium state. We investigate the formulation derived from kinetic theory, using the Chapman-Enskog expansion, in [Phys. Rev. C 88, 021903 (2013)] which was shown to be in excellent agreement with solutions of the microscopic theory. From this analysis, we demonstrate that this theory is linearly acausal and unstable and that such instabilities cannot be corrected by tuning the transport coefficients. We then propose a modification of this theory, valid only in the linear regime, that can be constructed to be linearly causal and stable and obtain the conditions the transport coefficients must satisfy in order for this to be the case.

New particles coupled to the Standard Model can equilibrate in stellar cores if they are sufficiently heavy and strongly coupled. In this work, we investigate the astrophysical consequences of such a scenario for massive stars by incorporating new contributions to the equation of state into a state of the art stellar structure code. We focus on axions in the “cosmological triangle,” a region of parameter space with $300\mathrm{keV}\lesssim m_a\lesssim 2\mathrm{MeV}$, $g_{a\gamma \gamma }\sim {10}^{-5}{\mathrm{GeV}}^{-1}$ that is not presently excluded by other considerations. We find that for axion masses $m_a\sim m_e$, axion production in the core drives a new stellar instability that results in explosive nuclear burning that either drives a series of mass-shedding pulsations or completely disrupts the star resulting in a new type of optical transient—an Axion Instability Supernova. We predict that the upper black hole mass gap would be located at $37{\mathrm{M}}_{\odot }\le M\le 107{\mathrm{M}}_{\odot }$ in these theories, a large shift down from the standard prediction, which is disfavored by the detection of the mass gap in the LIGO/Virgo/KAGRA GWTC-2 gravitational wave catalog beginning at ${46}_{-6}^{+17}{\mathrm{M}}_{\odot }$. Furthermore, axion-instability supernovae are more common than pair-instability supernovae, making them excellent candidate targets for James Webb Space Telescope. The methods presented in this work can be used to investigate the astrophysical consequences of any theory of new physics that contains heavy bosonic particles of arbitrary spin. We provide the tools to facilitate such studies.

We calculate the contribution to the baryon asymmetry of the Universe (BAU) from a $CP$-violating source of the light quarks (charm, strange, down, up) and the electron, resulting from a dimension-six effective field theory term. We derive relevant bounds from the electric dipole moments of the electron and neutron to estimate the maximal contribution from each single-flavor modification. Current bounds show that the charm quark can generate at most $\mathcal{O}(1\%)$ of the BAU, while the lighter quarks and the electron contribute at much lower levels.

The recently proposed multiphase criticality principle in Coleman-Weinberg models can provide a new explanation for the hierarchy between the electroweak and new physics scales. When applied to the Standard Model, a Higgs boson as light as the pseudo-Goldstone boson of broken-scale invariance occurs. The suppressed mixing between the two light fields still carries information about the large scale of symmetry breaking, albeit up to logarithmic corrections. In this work we probe this scenario with the present LHC data and assess the impact of future lepton and hadron colliders. Our results show that the multiphase criticality can easily explain the apparent absence of new physics at the energy scales tested in current experiments.

Large liquid scintillator detectors, such as JUNO, present a new opportunity to study neutral current events from the low-energy end of the atmospheric neutrinos, and possible new physics signals due to light dark matter. We carefully study the possibility of detecting “large-energy singles” (LES), i.e., events with visible scintillation energy $>15\mathrm{MeV}$, but no other associated tags. For an effective exposure of $20\mathrm{kton}-\mathrm{yr}$ and considering only Standard Model physics, we expect the LES sample to contain $\sim 40$ events from scattering on free protons and $\sim 108$ events from interaction with carbon, from neutral-current interactions of atmospheric neutrinos. Backgrounds, largely due to $\beta$ decays of cosmogenic isotopes, are shown to be significant only below 15 MeV visible energy. The LES sample at JUNO can competitively probe a variety of new physics scenarios, such as boosted dark matter and annihilation of galactic dark matter to sterile neutrinos.

We evaluate the leading-order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon with two light flavors in minimal hard-wall and soft-wall holographic QCD models, as well as in simple generalizations thereof, and compare it to the rather precise results available from dispersive and lattice approaches. While holographic QCD cannot be expected to shed light on the existing small discrepancies between the latter, this comparison in turn provides useful information on the holographic models, which have been used to evaluate hadronic light-by-light contributions where errors in data-driven and lattice approaches are more sizable. In particular, in the hard-wall model that has recently been used to implement the Melnikov-Vainshtein short-distance constraint on hadronic light-by-light contributions, a matching of the hadronic vacuum polarization to the data-driven approach points to the same correction of parameters that has been proposed recently in order to account for next-to-leading-order effects.

The effective potential of the standard model of electroweak unification is determined at two-loop order in a linear gauge involving two massless and two massive gauge fixing parameters. The divergent and logarithmic terms involving the massive gauge parameters are found to be determined also by the gauge parameter identities. The renormalization group method for summing logarithms is shown to be applicable also at scales below that of the massive gauge parameters.

A measurement of the ratios of the effective decay widths of $D^0\to {\pi }^{-}{\pi }^{+}$ and $D^0\to K^{-}{K}^{+}$ decays over that of $D^0\to K^{-}{\pi }^{+}$ decays is performed with the LHCb experiment using proton–proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$. These observables give access to the charm mixing parameters $y_{CP}^{\pi \pi }-y_{CP}^{K\pi }$ and $y_{CP}^{KK}-y_{CP}^{K\pi }$, and are measured as $y_{CP}^{\pi \pi }-y_{CP}^{K\pi }=(6.57\pm 0.53\pm 0.16)\times {10}^{-3}$, $y_{CP}^{KK}-y_{CP}^{K\pi }=(7.08\pm 0.30\pm 0.14)\times {10}^{-3}$, where the first uncertainties are statistical and the second systematic. The combination of the two measurements is $y_{CP}-y_{CP}^{K\pi }=(6.96\pm 0.26\pm 0.13)\times {10}^{-3}$, which is four times more precise than the previous world average.

A search is made for a vectorlike $T$ quark decaying into a Higgs boson and a top quark in 13 TeV proton-proton collisions using the ATLAS detector at the Large Hadron Collider with a data sample corresponding to an integrated luminosity of $139{\mathrm{fb}}^{-1}$. The Higgs-boson and top-quark candidates are identified in the all-hadronic decay mode, where $H\to b\overline{b}$ and $t\to bW\to bq{\overline{q}}^{\prime }$ are reconstructed as large-radius jets. The candidate Higgs boson, top quark, and associated $B$ hadrons are identified using tagging algorithms. No significant excess is observed above the background, so limits are set on the production cross section of a singlet $T$ quark at 95% confidence level, depending on the mass $m_T$ and coupling ${\kappa }_T$ of the vectorlike $T$ quark to Standard Model particles. In the considered mass range between 1.0 and 2.3 TeV, the upper limit on the allowed coupling values increases with $m_T$ from a minimum value of 0.35 for $1.07<m_T<1.4\mathrm{TeV}$ to 1.6 for $m_T=2.3\mathrm{TeV}$.

That the exact quantum S-matrix of $\mathrm{T}\overline{\mathrm{T}}$-deformed field theories is known has interesting consequences for their perturbative renormalization. Recent investigations into the interplay between renormalization and integrable deformations have focused on those cases where the (undeformed) seed theories are integrable. In this paper, we study the perturbative renormalization of nonintegrable $\mathrm{T}\overline{\mathrm{T}}$-deformed field theories, focusing on a theory of scalars with a quartic interaction. We show that in this theory, the 4-point 1-loop S-matrix exhibits features similar to its integrable cousins. We also carry out a similar analysis for the case of an integrable quantum field theory comprising a pair of chiral bosons. Our discussion of this latter theory supplies the first explicit example of a perturbative field theory computation in the formalism due to Sen.

In this paper we consider the non-Abelian T-dual geometry of the type $IIB$ supergravity theory on ${\mathrm{AdS}}_3\times S^3\times T^4$ background along a convenient $SU(2)$ subgroup of the $SO(4)$ R-symmetry. We examine various null geodesics of the resulting massive type $IIA$ supergravity theory and investigate the Penrose limits along these geodesics. We find that one of the resulting backgrounds admits pp-wave geometry in the neighborhood of a suitable null geodesic. We carry out the supersymmetry analysis of the resulting pp-wave geometry and observe that it preserves sixteen supercharges. Further we comment on the possible gauge theory dual of the resulting pp-wave background.

Dynamical realizations of the Lifshitz group are studied within the group-theoretic framework. A generalization of the $1d$ conformal mechanics is constructed, which involves an arbitrary dynamical exponent $z$. A similar generalization of the Ermakov-Milne-Pinney equation is proposed. Invariant derivative and field combinations are introduced, which enable one to construct a plethora of dynamical systems enjoying the Lifshitz symmetry. A metric of the Lorentzian signature in ($d+2$)-dimensional spacetime and the energy-momentum tensor are constructed, which lead to the generalized Ermakov-Milne-Pinney equation upon imposing the Einstein equations. The method of nonlinear realizations is used for building Lorentzian metrics with the Lifshitz isometry group. In particular, a ($2d+2$)-dimensional metric is constructed, which enjoys an extra invariance under the Galilei boosts.

The weak-gravity bound has been discovered in asymptotically safe gravity-matter systems, where it limits the maximum strength of gravitational fluctuations. In the present paper, we explore it for the first time in systems with more than one gauge field to discover whether systems with 12 gauge fields (like the Standard Model) exhibit a weak-gravity bound and whether the gravitational fixed point evades it. Further, we test the robustness of the present and previous results on the weak-gravity bound by exploring their dependence on a gravitational gauge parameter. Finally, the existence of the weak-gravity bound also has important phenomenological consequences: it is key to a proposed mechanism that bounds the spacetime dimensionality from above to four or five dimensions. In this paper, we strengthen the evidence for this mechanism. Thus, the predictive power of the asymptotic safety paradigm could extend to parameters of the spacetime geometry, such that the four dimensionality of our Universe could be explained from first principles.

Recently, by explicit calculations at orders ${\alpha }^{\prime },{\alpha }^{\prime 2},{\alpha }^{\prime 3}$, it has been observed that the effective action of string theory at the critical dimension is independent of the background for the closed spacetime manifolds. In this paper we speculate that for the open spacetime manifolds, the effective action is even independent of the character of the boundary, i.e., the boundary couplings for timelike and spacelike boundaries are the same. We support this proposal by calculating the boundary couplings in the bosonic string theory at order ${\alpha }^{\prime }$ for the spacelike boundary and show that they are the same as the couplings for the timelike boundary that have been recently found.

A fundamental description of time can be consistent not only with the usual monotonic behavior but also with an oscillating physical clock variable, coupled to the degrees of freedom of a system evolving in time. Generically, one would in fact expect some kind of oscillating motion of a system that is dynamical and interacts with its surroundings, as required for a fundamental clock that can be noticed by any other system. Unitary evolution does not require a monotonic clock variable and can be achieved more generally by formally unwinding the oscillating clock movement, keeping track not only of the value of the clock variable but also of the number of cycles it has gone through at any moment. The specific treatment used here employs concatenations of evolution operators, alternating between forward and backward evolution of the oscillating clock. Because the clock and an evolving system have a common conserved energy, the clock is in different cycles for different energy eigenstates of the system state. As a result, the clock is generically in a quantum state with a superposition of different clock cycles, a key feature that distinguishes oscillating clocks from monotonic time. In addition, coherence could be lost faster than observed, for instance if a system that would be harmonic in isolation is made anharmonic by interactions with a fundamental clock, implying observational bounds on fundamental clocks. Numerical computations show that coherence is maintained over long timescales provided the clock period is much smaller than the system period. A small loss of coherence nevertheless remains and, measured in terms of the relative standard deviation of the system period, is proportional to the ratio of the system period and the clock period. Since the precision of atomic clocks could not be achieved if atomic frequencies would be subject to additional variations from coupling to a fundamental clock, an upper bound on the clock period can be obtained that turns out to be much smaller than currently available direct or indirect measurements of time.

We investigate the response of a model gravitational wave detector consisting of two particles to the quantized cylindrical gravitational waves and obtain a relation between the standard deviation of the distance between two particles and the distance from the source to the detector. It is found that the quantum effect carried by the cylindrical gravitational wave can be observed above Planck scale even though the source is as far as the cosmological horizon. The equation of motion for the change of the distance between two particles is obtained when the cylindrical gravitational waves pass. It is surprising that the dissipative term does not exist up to the first order approximation due to cylindrical symmetry of the gravitational wave.

Interactions growing slower than a certain exponential of the square of a scalar field are well behaved when evolved under the functional renormalization group linearized around the Gaussian fixed point. They satisfy properties usually taken for granted, and reproduce standard perturbative quantization. However, the more challenging effects appear, the more interactions grow faster than this. We show explicitly that firstly, the flow no longer splits uniquely into operators of definite scaling dimension; secondly, (linearized) flows to the infrared can end prematurely in a singularity; and finally, new interactions can spontaneously appear at any scale.

Motivated by the possibility to use Bose-Einstein condensates as quantum simulators for spacetime curvature, we study a massless relativistic scalar quantum field in spatially curved Friedmann-Lemaître-Robertson-Walker universes with $d=2+1$ spacetime dimensions. In particular, we investigate particle production caused by a time-dependent background geometry, by means of the spectrum of fluctuations and several two-point field correlation functions. We derive new analytical results for several expansion scenarios.

We study the consistency of the decoupling limit of the generalized SU(2) Proca theory (GSU2P). Namely, we study the healthiness of those terms whose analysis in the scalar limit was not originally established in the reconstruction of the full theory (see the work by Gallego Cadavid et al. [Phys. Rev. D 102, 104066 (2020)]). Those terms are the parity-violating ${\tilde{\mathcal{L}}}_{4,2}^1$ and the parity-conserving beyond SU(2) Proca terms ${\mathcal{L}}_{4,2}^3$ and ${\mathcal{L}}_{4,2}^4$. Using the $3+1$ Arnowitt-Deser-Misner formalism, we write down the kinetic Lagrangian of these terms in the decoupling limit and show that their corresponding kinetic matrices are degenerate. This degeneracy is a necessary condition for the propagation of the right number of degrees of freedom, as required by the primary constraint-enforcing relation. Interestingly, the ${\tilde{\mathcal{L}}}_{4,2}^1$ term, which is purely non-Abelian, does not contribute to the kinetic Lagrangian of the theory, so its contribution is trivially degenerate. Similarly, but not trivially in these cases, the contributions of the ${\mathcal{L}}_{4,2}^3$ and ${\mathcal{L}}_{4,2}^4$ terms to the kinetic Lagrangian turn out to be degenerate as well. The results presented in this paper represent progress in the construction of the fully healthy GSU2P.

Energies for constantly accelerating observers in Bañados, Teitelboim, and Zanelli; Schwarzschild; and Schwarzschild–de Sitter spacetimes are derived. The expressions are in terms of acceleration, cosmological constant, and area, quantities measurable by the observers. Based on results from quantum fields in curved spacetime for the redshifted Hawking temperature, quasilocal entropy and thermodynamic-like laws are briefly explored in the three spacetimes.