Gravitational Raman Scattering in Effective Field Theory: A Scalar Tidal Matching at O(G

We present a framework to compute amplitudes for the gravitational analog of the Raman process, a quasielastic scattering of waves off compact objects, in worldline effective field theory. As an example, we calculate third post-Minkowskian order [O(G^{3})], or two-loop, phase shifts for the scattering of a massless scalar field including all tidal effects and dissipation. Our calculation unveils two sources of the classical renormalization-group flow of dynamical Love numbers: a universal running independent of the nature of the compact object, and a running self-induced by tides. Restricting to the black hole case, we find that our effective field theory phase shifts agree exactly with those from general relativity, provided that the relevant static Love numbers are set to zero. In addition, we carry out a complete matching of the leading scalar dynamical Love number required to renormalize a universal short scale divergence in the S wave. Our results pave the way for systematic calculations of gravitational Raman scattering at higher post-Minkowskian orders.

Effective Field Theory for Extreme Mass Ratio Binaries.

We derive an effective field theory describing a pair of gravitationally interacting point particles in an expansion in their mass ratio, also known as the self-force (SF) expansion. The 0SF dynamics are trivially obtained to all orders in Newton's constant by the geodesic motion of the light body in a Schwarzschild background encoding the gravitational field of the heavy body. The corrections at 1SF and higher are generated by perturbations about this configuration-that is, the geodesic deviation of the light body and the fluctuation graviton-but crucially supplemented by an operator describing the recoil of the heavy body as it interacts with the smaller companion. Using this formalism we compute new results at third post-Minkowskian order for the conservative dynamics of a system of gravitationally interacting massive particles coupled to a set of additional scalar and vector fields.

Nonperturbative Double Copy in Flatland.

We derive a nonperturbative, Lagrangian-level formulation of the double copy in two spacetime dimensions. Our results elucidate the field theoretic underpinnings of the double copy in a broad class of scalar theories which can include masses and higher-dimension operators. An immediate corollary is the amplitudes-level double copy at all orders in perturbation theory. Applied to certain integrable models, the double copy defines an isomorphism between Lax connections, Wilson lines, and infinite towers of conserved currents. We also implement the double copy at the level of nonperturbative classical solutions, both analytically and numerically, and present a generalization of the double copy map that includes a fixed tower of higher-dimension corrections given by the Moyal algebra.

Scattering Amplitudes, the Tail Effect, and Conservative Binary Dynamics at O(G

We complete the calculation of conservative two-body scattering dynamics at fourth post-Minkowskian order, i.e., O(G^{4}) and all orders in velocity, including radiative contributions corresponding to the tail effect in general relativity. As in previous calculations, we harness powerful tools from the modern scattering amplitudes program including generalized unitarity, the double copy, and advanced multiloop integration methods, in combination with effective field theory. The classical amplitude involves complete elliptic integrals, and polylogarithms with up to transcendental weight 2. Using the amplitude-action relation, we obtain the radial action directly from the amplitude, and match the known overlapping terms in the post-Newtonian expansion.

Gravitational Bremsstrahlung from Reverse Unitarity.

We compute the total radiated momentum carried by gravitational waves during the scattering of two spinless black holes at the lowest order in Newton's constant, O(G^{3}), and all orders in velocity. By analytic continuation into the bound state regime, we obtain the O(G^{3}) energy loss in elliptic orbits. This provides an essential step toward the complete understanding of the third-post-Minkowskian binary dynamics. We employ the formalism of Kosower, Maybee, and O'Connell (KMOC), which relates classical observables to quantum scattering amplitudes, and derive the relevant integrands using generalized unitarity. The subsequent phase-space integrations are performed via the reverse unitarity method familiar from collider physics, using differential equations to obtain the exact velocity dependence from near-static boundary conditions.

Scattering Amplitudes and Conservative Binary Dynamics at O(G

Using scattering amplitudes, we obtain the potential contributions to conservative binary dynamics in general relativity at fourth post-Minkowskian order O(G^{4}). As in previous lower-order calculations, we harness powerful tools from the modern scattering amplitudes program including generalized unitarity, the double copy, and advanced multiloop integration methods, in combination with effective field theory. The classical amplitude involves polylogarithms with up to transcendental weight two and elliptic integrals. We derive the radial action directly from the amplitude, and determine the corresponding Hamiltonian in isotropic gauge. Our results are in agreement with known overlapping terms up to sixth post-Newtonian order, and with the probe limit. We also determine the post-Minkowskian energy loss from radiation emission at O(G^{3}) via its relation to the tail effect.

Universality in the Classical Limit of Massless Gravitational Scattering.

We demonstrate the universality of the gravitational classical deflection angle of massless particles through O(G^{3}) by studying the high-energy limit of full two-loop four-graviton scattering amplitudes in pure Einstein gravity as well as N≥4 supergravity. As a by-product, our first-principles calculation provides a direct confirmation of the massless deflection angle in Einstein gravity proposed long ago by Amati, Ciafaloni, and Veneziano, and is inconsistent with a recently proposed alternative.

Signo de la arteria cerebral posterior hiperdensa migratoria tras trombólisis intravenosa / Migratory hyperdense posterior cerebral artery sign following intravenous thrombolysis

INTRODUCCIÓN: La tomografía computarizada cerebral sigue siendo la modalidad de imagen básica en la fase aguda del ictus. El signo de la arteria cerebral posterior hiperdensa es un hallazgo radiológico precoz e infrecuente con valor topográfico y pronóstico que hay que tener en cuenta en las tomografías computarizadas iniciales. CASO CLÍNICO: Mujer de 79 años, que presenta de forma brusca una hemianopsia homónima izquierda, leve paresia facial inferior izquierda, hemiparesia izquierda 3/5 y grave hipoestesia izquierda. En la tomografía computarizada cerebral inicial se objetiva hiperdensidad cálcica del segmento P1 de la arteria cerebral posterior derecha. Se administra fibrinolítico intravenoso. Presenta mejoría clínica, y en la tomografía computarizada cerebral de control 24 horas después de la fibrinólisis se observa hiperdensidad del segmento P3 de la arteria cerebral posterior derecha. CONCLUSIONES: La evidencia de una hiperdensidad de la arteria cerebral posterior es un hallazgo radiológico infrecuente asociado a un mayor volumen de infarto isquémico. La tomografía computarizada cerebral en fase aguda resulta fundamental para tratar de dilucidar su etiología. Los émbolos cálcicos son una causa infradiagnosticada de ictus y ocurren de forma espontánea en una gran proporción. Ante la sospecha de embolismo cálcico, es necesario realizar un estudio en busca de una patología carotídea, valvular o del arco aórtico. La migración de la hiperdensidad arterial hacia distal en la tomografía computarizada se relaciona con un mejor pronóstico. Este caso presentó una buena evolución frente al mal pronóstico descrito en la bibliografía en casos de hiperdensidad arterial como marcador precoz de ictus en fase aguda

INTRODUCTION: Computed tomography (CT) scanning of the brain continues to be the basic imaging mode in the acute phase of stroke. The hyperdense posterior cerebral artery sign is an early and infrequent radiological finding with topographic and prognostic value that must be taken into account in the initial CT scans. CASE REPORT: We report the case of a 79-year-old woman who suddenly presented with severe left homonymous hemianopsia, mild lower left facial paresis, 3/5 left hemiparesis and severe left hypaesthesia. In the initial brain CT scan, calcium hyper¬density of the P1 segment is observed in the right posterior cerebral artery. Intravenous fibrinolytic therapy is administered. The patient shows clinical improvement, and in the follow-up brain CT scan at 24 hours after fibrinolysis, hyperdensity of the P3 segment is observed in the right posterior cerebral artery. CONCLUSIONS: Evidence of posterior cerebral artery hyperdensity is a rare radiological finding associated with an increased volume of ischaemic stroke. A computed tomography scan of the head in the acute phase is essential to try to clarify its causation. Calcium emboli are an under-diagnosed cause of stroke and occur spontaneously in a large proportion of cases. If calcium embolism is suspected, a study must be conducted in search of a carotid, valvular or aortic arch pathology. Migration of the arterial hyperdensity towards distal is associated with a better prognosis. This case presented good progress in contrast to the poor prognosis described in the literature in cases of arterial hyperdensity as an early marker of stroke in the acute phase

Classification of String Theories via Topological Phases.

We point out that the choice of phases in Gliozzi-Scherk-Olive projections can be accounted for by a choice of fermionic symmetry-protected topological phases on the world sheet of the string. This point of view not only easily explains why there are essentially two type II theories, but also predicts that there are unoriented type 0 theories labeled by n mod 8 and that there is an essentially unique choice of the type I world sheet theory. We also discuss the relationship between this point of view and the K-theoretic classification of D-branes.

Two-loop n-point anomalous amplitudes in N = 4 supergravity.

We compute the anomalous two-loop four-point amplitudes in N = 4 pure supergravity, using unitarity and the double-copy construction. We also present all terms determined by four-dimensional cuts in two all-multiplicity two-loop anomalous superamplitudes. This result provides the first two-loop n-point gravity amplitude, up to a class of undetermined terms, which we determine completely at four points. We show that a recently proposed finite counterterm cancels these amplitudes to this order. We argue that the counterterm does not spoil the three-loop finiteness of anomalous amplitudes in the N = 4 theory.

Nonrenormalization and Operator Mixing via On-Shell Methods.

Using on-shell methods, we present a new perturbative nonrenormalization theorem for operator mixing in massless four-dimensional quantum field theories. By examining how unitarity cuts of form factors encode anomalous dimensions, we show that longer operators are often restricted from renormalizing shorter operators at the first order where Feynman diagrams exist. The theorem applies quite generally and depends only on the field content of the operators involved. We apply our theorem to operators of dimension five through seven in the standard model effective field theory, including examples of nontrivial zeros in the anomalous-dimension matrix at one through four loops. The zeros at two and higher loops go beyond those previously explained using helicity selection rules. We also include explicit sample calculations at two loops.

Canceling the U(1) Anomaly in the S Matrix of N=4 Supergravity.

N=4 supergravity is understood to contain a U(1) anomaly which manifests itself via the nonvanishing of loop-level scattering amplitudes that violate a tree-level charge conservation rule. In this Letter we provide detailed evidence that at one loop such anomalous amplitudes can be set to zero by the addition of a finite local counterterm. We show that the same counterterm also cancels evanescent contributions that play an important role in the analysis of ultraviolet divergences in dimensionally regularized gravity. These cancellations call for a reanalysis of the four-loop ultraviolet divergences previously found in this theory without the addition of such counterterms.