192 research outputs found
String Lessons for Higher-Spin Interactions
No full textString Theory includes a plethora of higher--spin excitations, which clearly lie behind its most spectacular properties, but whose detailed behavior is largely unknown. Conversely, string interactions contain much useful information on higher--spin couplings, which can be very valuable in current attempts to characterize their systematics. We present a simplified form for the three--point (and four--point) amplitudes of the symmetric tensors belonging to the first Regge trajectory of the open bosonic string and relate them to local couplings and currents. These include the cases first discussed, from a field theory perspective, by Berends, Burgers and van Dam, and generalize their results in a suggestive fashion along lines recently explored by Boulanger, Metsaev and others. We also comment on the recovery of gauge symmetry in the low--tension limit, on the current--exchange amplitudes that can be built from these couplings and on the extension to mixed--symmetry states
Strategie progettuali per una rete virtuosa nelle terre alte d'Abruzzo tra Roccaraso, Rivisondoli e Pescocostanzo
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On the consistency of (partially-)massless matter couplings in de Sitter space
No full textAbstract We study the consistency of the cubic couplings of a (partially-)massless spinning field to two scalars in (d + 1)-dimensional de Sitter space. Gauge invariance of observables with external (partially)-massless spinning fields translates into Ward-Takahashi identities on the boundary. Using the Mellin-Barnes representation for boundary correlators in momentum space, we give a systematic study of Ward-Takahashi identities for tree-level 3- and 4-point processes involving a single external (partially-)massless field of arbitrary integer spin-J. 3-point Ward-Takahashi identities constrain the mass of the scalar fields to which a (partially-)massless spin-J field can couple. 4-point Ward-Takahashi identities then constrain the corresponding cubic couplings. For massless spinning fields, we show that Weinberg’s flat space results carry over to (d+1)-dimensional de Sitter space: for spins J = 1, 2 gauge-invariance implies charge-conservation and the equivalence principle while, assuming locality, higher-spins J > 2 cannot couple consistently to scalar matter. This result also applies to anti-de Sitter space. For partially-massless fields, restricting for simplicity to those of depth-2, we show that there is no consistent coupling to scalar matter in local theories. Along the way we also give a detailed account of how contact amplitudes with and without derivatives are represented in the Mellin-Barnes representation. Various new explicit expressions for 3- and 4-point functions involving (partially-)massless fields and conformally coupled scalars in dS4 are given
From dS to AdS and back
No full textWe describe in more detail the general relation uncovered in our previous work between boundary correlators in de Sitter (dS) and in Euclidean anti-de Sitter (EAdS) space, at any order in perturbation theory. Assuming the Bunch-Davies vacuum at early times, any given diagram contributing to a boundary correlator in dS can be expressed as a linear combination of Witten diagrams for the corresponding process in EAdS, where the relative coefficients are fixed by consistent on-shell factorisation in dS. These coefficients are given by certain sinusoidal factors which account for the change in coefficient of the contact sub-diagrams from EAdS to dS, which we argue encode (perturbative) unitary time evolution in dS. dS boundary correlators with Bunch-Davies initial conditions thus perturbatively have the same singularity structure as their Euclidean AdS counterparts and the identities between them allow to directly import the wealth of techniques, results and understanding from AdS to dS. This includes the Conformal Partial Wave expansion and, by going from single-valued Witten diagrams in EAdS to Lorentzian AdS, the Froissart-Gribov inversion formula. We give a few (among the many possible) applications both at tree and loop level. Such identities between boundary correlators in dS and EAdS are made manifest by the Mellin-Barnes representation of boundary correlators, which we point out is a useful tool in its own right as the analogue of the Fourier transform for the dilatation group. The Mellin-Barnes representation in particular makes manifest factorisation and dispersion formulas for bulk-to-bulk propagators in (EA)dS, which imply Cutkosky cutting rules and dispersion formulas for boundary correlators in (EA)dS. Our results are completely general and in particular apply to any interaction of (integer) spinning fields
Shaping translingual writing and translation as intersectional practices: Nadeesha Uyangoda’s L’unica persona nera nella stanza and Sulla razza as case studies
No full textThis article takes into consideration those studies which have contributed to the development of an intersectional approach to translingual writing and translation by envisioning a new conception of language as a place to be shared and a border to be crossed, as well as a tool to interrogate the intertwined categories of race and gender. Specifically, it analyses Nadeesha Uyangoda’s memoir L’unica persona nera nella stanza (The Only Black Person in the Room) along with the podcast Sulla razza (About Race), written and co-hosted by the same author with Natasha Fernando and Maria Catena Mancuso. Both productions focus on the lived experience of Black, Asian and minority ethnic (BAME) women in Italy who articulate, question, and re-imagine notions of race, ethnicity, citizenship, identity, belonging, and homemaking, while publicly denouncing power imbalances and acts of injustice. The memoir and the podcast also highlight the resonance that Black Italians may have in the contemporary Italian political context
Re-Active Schools. Sperimentazioni metodologiche e progettuali per il patrimonio scolastico nell’Italia sismica
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