Journal of High Energy Physics最新文献

We derive a lower bound on the sensitivity of generic mechanical and electromagnetic gravitational wave detectors. We consider both classical and quantum detection schemes, although we focus on the former. Our results allow for a simple reproduction of the sensitivities of a variety of experiments, including optical interferometers, resonant bars, optomechanical sensors, and electromagnetic conversion experiments. In the high-frequency regime, all detection schemes we consider can be characterised by their stored electromagnetic energy and the signal transfer function, which we provide. We discuss why high-frequency gravitational wave searches are especially difficult and primordial gravitational wave backgrounds might not be detectable above the sensitivity window of existing interferometers.

Quantum theories of gravity are generally expected to have some degree of non-locality, with familiar local physics emerging only in a particular limit. Perturbative quantum gravity around backgrounds with isometries and compact Cauchy slices provides an interesting laboratory in which this emergence can be explored. In this context, the remaining isometries are gauge symmetries and, as a result, gauge-invariant observables cannot be localized. Instead, local physics can arise only through certain relational constructions.

We explore such issues below for perturbative quantum gravity around de Sitter space. In particular, we describe a class of gauge-invariant observables which, under appropriate conditions, provide good approximations to certain algebras of local fields. Our results suggest that, near any minimal S^d in dS_d+1, this approximation can be accurate only over regions in which the corresponding global time coordinate t spans an interval ∆t ≲ O(ln G⁻¹). In contrast, however, we find that the approximation can be accurate over arbitrarily large regions of global dS_d+1 so long as those regions are located far to the future or past of such a minimal S^d. This in particular includes arbitrarily large parts of any static patch.

We revisit the Berenstein-Maldacena-Nastase (BMN) conjecture relating M-theory on a PP-wave background and Matrix Quantum Mechanics (MQM) of N × N matrices. In particular, we study the BMN MQM at strong coupling and finite N and derive an effective Hamiltonian that describes non-relativistic free particles in a harmonic trap. The energy spectrum predicted by this Hamiltonian matches the supergravity excitation spectrum around the PP-wave background, if we further assume the existence of bound states. Our derivation is based on the strong coupling expansion of the wavefunction and supersedes the naive path integral approach that can lead to incorrect results, as we demonstrate in a simple toy model. We conclude with open questions about various regimes of the theory when we vary the size of the matrices, the coupling and the temperature.

High-energy factorization of 2 → 2 amplitudes in QCD has been recently pushed to the next-to-next-to-leading logarithmic order by determining the three-loop gluon Regge trajectory. This was based on computing multi-Reggeon exchanges using rapidity evolution in the shock-wave formalism, and disentangling between the Regge pole and Regge cut contributions. In the present paper we extend the relevant theoretical framework to 2 → 3 processes, and compute all multi-Reggeon exchanges necessary for extracting the two-loop Reggeon-gluon-Reggeon Lipatov vertex from 2 → 3 amplitudes. Then, specializing general amplitude methods to multi-Regge kinematics, we derive analytic expressions for non-planar two-loop gg → ggg, gq → ggq and qq → qgq QCD amplitudes in that limit. Matching these to the multi-Reggeon computation, we determine the QCD Lipatov vertex in dimensional regularization at two loops through finite terms. We also determine the one-loop vertex through ( mathcal{O} )(ϵ⁴). All results are expressed in a compact form in terms of a basis of single-valued generalised polylogarithms, manifesting target-projectile symmetry and reality properties. Furthermore, our basis of functions is explicitly finite in the soft limit, featuring delicate cancellation of spurious rational poles by transcendental functions. Agreement between all three partonic channels, as well agreement of the maximal weight contributions with the super Yang-Mills Lipatov vertex provide robust checks of the result.

We present minimally supersymmetric AdS₄ flux vacua derived from massive type IIA compactified on T⁶/ℤ₃ × ℤ₃ orbifold, characterized by unconstrained fluxes with general scalings. We discover anisotropic scaling solutions in which scale separation is realized in the supergravity limit, and the subvolumes of the internal space become large and anisotropic in this limit. Additionally, we identify further regimes in which subvolumes either shrink or remain constant, while scale separation is either broken or realized for large values of the unconstrained fluxes. Then, we employ a probe D4-brane to interpolate between vacua, finding that it interpolates through the regimes we previously identified. Finally, we utilize an open string modulus of the D4-brane to calculate the distance between anisotropic vacua for the regime where scale separation is realized in the supergravity limit. We show the dependence of both the geodesic distance and the Distance Conjecture parameter on the unconstrained flux scalings.

Dense neutrino gases can exhibit collective flavor instabilities, triggering large flavor conversions that are driven primarily by neutrino-neutrino refraction. One broadly distinguishes between fast instabilities that exist in the limit of vanishing neutrino masses, and slow ones, that require neutrino mass splittings. In a related series of papers, we have shown that fast instabilities result from the resonant growth of flavor waves, in the same way as turbulent electric fields in an unstable plasma. Here we extend this framework to slow instabilities, focusing on the simplest case of an infinitely homogeneous medium with axisymmetric neutrino distribution. The relevant length and time scales are defined by three parameters: the vacuum oscillation frequency ω_E = δm²/2E, the scale of neutrino-neutrino refraction energy ( mu =sqrt{2}{G}_{textrm{F}}left({n}_{nu }+{n}_{overline{nu}}right) ), and the ratio between lepton and particle number ( epsilon =left({n}_{nu }-{n}_{overline{nu}}right)/left({n}_{nu }+{n}_{overline{nu}}right) ). We distinguish between two very different regimes: (i) For ω_E ≪ μϵ², instabilities occur at small spatial scales of order (μϵ)⁻¹ with a time scale of order ( epsilon {omega}_E^{-1} ). This novel branch of slow instability arises from resonant interactions with neutrinos moving along the axis of symmetry. (ii) For μϵ² ≪ ω_E ≪ μ, the instability is strongly non-resonant, with typical time and length scales of order ( 1/sqrt{omega_Emu } ). Unstable modes interact with all neutrino directions at once, recovering the characteristic scaling of the traditional studies of slow instabilities. In the inner regions of supernovae and neutron-star mergers, the first regime may be more likely to appear, meaning that slow instabilities in this region may have an entirely different character than usually envisaged.

We investigate the fermionic perturbations of the asymptotically AdS background known as holographic neutron star, which represents a highly degenerate state of strongly coupled fermions on a sphere at finite temperature. We calculate the two-point correlator of a fermionic operator and obtain its scaling properties as we approach the critical region of the phase diagram.

We show that near the edges of the conformal window of supersymmetric SU(N_c) QCD, perturbed by Anomaly Mediated Supersymmetry Breaking (AMSB), chiral symmetry can be broken depending on the initial conditions of the RG flow. We do so by perturbatively expanding around Banks-Zaks fixed points and taking advantage of Seiberg duality. Interpolating between the edges of the conformal window, we predict that non-supersymmetric QCD breaks chiral symmetry up to N_f ≤ 3N_c − 1, while we cannot say anything definitive for N_f ≥ 3N_c at this moment.

We investigate multi-lepton jet events from the decay of the 125 GeV Higgs boson (h) into quadruple new gauge bosons (Z′) at the LHC. Such an exotic decay is realized via the process of h → ϕϕ → Z′Z′Z′Z′ with new scalar boson ϕ in models with an additional U(1) gauge symmetry. Charged leptons coming from the Z′ decay tend to be observed as lepton-jets rather than isolated leptons when the masses of Z′ and ϕ are smaller than ( mathcal{O} )(10) GeV, because of the highly-boosted effects. Performing the signal and background analyses, we find that the branching ratio of h → 4Z′ is maximally constrained to be smaller than of order 10⁻⁶ (10⁻⁷) by using the muonic-lepton jets assuming the integrated luminosity of 140 fb⁻¹ (3000 fb⁻¹) at LHC. For lighter Z′ (< 2m_μ), we can use the electronic-lepton jets instead of the muon-jets, by which the upper limit on the branching ratio is obtained to be of order 10⁻⁶–10⁻⁵. These bounds can be converted into the constraint on model parameters such as a mixing angle between h and ϕ. It is shown that stronger bounds on the mixing angle are obtained in the dark photon case as compared with the previous constraints given by flavor experiments and the Higgs decay h → Z′Z′ in the mass range of ( {m}_{Z^{prime }} ) ≲ 10 GeV.

Near the horizon of extremal charged black holes, an accidental symmetry is known to act on zero-temperature perturbations, transforming them into finite-temperature ones. In this paper, we uncover the corresponding accidental symmetry of the vacuum Einstein equation near the horizon of extremal spinning black holes. To do so, we first devise a new method of deriving the symmetry near the AdS₂ × S² near-horizon geometry of extreme Reissner-Nordström, using a new scaling coordinate transformation that unifies the near-horizon limits of extremal and near-extremal black holes in a way that is regular at zero temperature. We use our new method to obtain the accidental symmetry in the near-horizon of extreme Kerr (NHEK). We show that accidental symmetries combine neatly with the near-horizon isometries inside a Virasoro algebra.