No Arabic abstract
We investigate the constraints imposed by global gravitational anomalies on parity odd induced transport coefficients in even dimensions for theories with chiral fermions, gravitinos and self dual tensors. The $eta$-invariant for the large diffeomorphism corresponding to the $T$ transformation on a torus constraints the coefficients in the thermal effective action up to mod 2. We show that the result obtained for the parity odd transport for gravitinos using global anomaly matching is consistent with the direct perturbative calculation. In $d=6$ we see that the second Pontryagin class in the anomaly polynomial does not contribute to the $eta$-invariant which provides a topological explanation of this observation in the `replacement rule. We then perform a direct perturbative calculation for the contribution of the self dual tensor in $d=6$ to the parity odd transport coefficient using the Feynman rules proposed by Gaum{e} and Witten. The result for the transport coefficient agrees with that obtained using matching of global anomalies.
Hairy black holes in the gravitational decoupling setup are studied from the perspective of conformal anomalies. Fluctuations of decoupled sources can be computed by measuring the way the trace anomaly-to-holographic Weyl anomaly ratio differs from unit. Therefore the gravitational decoupling parameter governing three hairy black hole metrics is then bounded to a range wherein one can reliably emulate AdS/CFT with gravitational decoupled solutions, in the tensor vacuum regime.
Recently, the relation between Hawking radiation and gravitational anomalies has been used to estimate the flux of Hawking radiation for a large class of black objects. In this paper, we extend the formalism, originally proposed by Robinson and Wilczek, to the Hawking radiation of vector particles (photons). It is explicitly shown, with Hamiltonian formalism, that the theory of an electromagnetic field on d-dimensional spherical black holes reduces to one of an infinite number of massive complex scalar fields on 2-dimensional spacetime, for which the usual anomaly-cancellation method is available. It is found that the total energy emitted from the horizon for the electromagnetic field is just (d-2) times as that for a scalar field. The results support the picture that Hawking radiation can be regarded as an anomaly eliminator on horizons. Possible extensions and applications of the analysis are discussed.
The presence of gravity generalizes the notion of scale invariance to Weyl invariance, namely, invariance under local rescalings of the metric. In this work, we have computed the Weyl anomaly for various classically scale or Weyl invariant theories, making particular emphasis on the differences that arise when gravity is taken as a dynamical fluctuation instead of as a non-dynamical background field. We find that the value of the anomaly for the Weyl invariant coupling of scalar fields to gravity is sensitive to the dynamical character of the gravitational field, even when computed in constant curvature backgrounds. We also discuss to what extent those effects are potentially observable.
We revisit the holographic description of the near horizon geometry of the BTZ black hole in AdS$_3$ gravity, with a gravitational Chern-Simons term included. After a dimensional reduction of the three dimensional theory, we use the framework of nAdS$_2$/nCFT$_1$ to describe the near horizon physics. This setup allows us to contrast the role of the gravitational and conformal anomaly inherited from AdS$_3$/CFT$_2$ in the symmetry breaking mechanism of nAdS$_2$/nCFT$_1$. Our results display how boundary conditions in the 3D spacetime, combined with the gravitational anomaly, affect the holographic description of the near horizon of the black hole relative to the physics near the AdS$_3$ boundary.
We reformulate the question of the absence of global anomalies of heterotic string theory mathematically in terms of a certain natural transformation $mathrm{TMF}^bulletto (I_{mathbb{Z}}Omega^text{string})^{bullet-20}$, from topological modular forms to the Anderson dual of string bordism groups, using the Segal-Stolz-Teichner conjecture. We will show that this natural transformation vanishes, implying that heterotic global anomalies are always absent. The fact that $mathrm{TMF}^{21}(mathrm{pt})=0$ plays an important role in the process. Along the way, we also discuss how the twists of $mathrm{TMF}$ can be described under the Segal-Stolz-Teichner conjecture, by using the result of Freed and Hopkins concerning anomalies of quantum field theories. The paper contains separate introductions for mathematicians and for string theorists, in the hope of making the content more accessible to a larger audience. The sections are also demarcated cleanly into mathematically rigorous parts and those which are not.