Found 9 result(s)

### 30.11.2021 (Tuesday)

#### Quasi-Normal Modes of Black-Holes and Branes from Quantum Seiberg-Witten Curves

Regular Seminar Massimo Bianchi (Universita degli studi di Roma Tor Vergata)

 at: 14:00 ICroom Online and H342 abstract: After reviewing the role Quasi-Normal Modes (QNMs) play in the Gravitational Wave (GW) signals emitted in the ring-down phase of Black-Hole (BH) mergers, we present a novel efficient approach to compute QNMs of BHs, D-branes and fuzz-balls, based on quantum Seiberg-Witten (SW) curves for N=2 supersymmetric Yang-Mills (SYM) theories. We find remarkable agreement with numerical results obtained by means of Leaver's method of continuous fractions and with semi-classical' results obtained in the eikonal approximation, based on geodetic motion. Finally we discuss the extension to D3-branes and their bound states of Couch-Torrence (CT) conformal inversions, that exchange horizon and infinity, and show that they keep the photon-sphere (or photon-halo) fixed.

### 21.03.2019 (Thursday)

#### From Soft Corrections to Ultra-Planckian Scattering and back

Regular Seminar Massimo Bianchi (Roma Tor Vergata)

 at: 14:00 QMWroom G O Jones 610 abstract: Ultra-planckian collisions represent a fertile arena where to test quantum theories of gravity such as string theory. Glimpses of black hole formation and evaporation can be taken. For suitably defined infrared-safe observables, we show that the classicalization' approach to high-multiplicity processes agrees with the ACV approach based on the resummation of ladder diagrams. Since a significant fraction of energy is lost in gravitational bremsstrahlung, we re-derived the zero-frequency limit (ZFL) of the GW flux using soft graviton theorems at leading order and compute the corrections at sub- and sub-sub-leading order. For massless two-particle elastic collisions the former is shown to vanish, while the latter takes an explicit expression which is checked against a simple tree-level process.However, if the tree-level form of the soft theorems is used at sub-sub-leading order even when the elastic amplitude needs resummation, an unphysical IR singularity occurs due to the infinite Coulomb phase. We briefly discuss a recent proposal as how to deal with these divergences and find agreement with the eikonal approach.

### 24.02.2016 (Wednesday)

#### Non-perturbative effective action of N=4 SYM in the Coulomb branch

Regular Seminar Massimo Bianchi (Rome (Tor Vergata))

 at: 14:00 ICroom H503 abstract: We derive the one-instanton effective action of N=4 super Yang-Mills theory in terms of the N=4 on-shell superfields. In the Coulomb branch, instantons correct both the MHV and next-to-next-MHV higher derivative terms D^4F^{2n+2} and F^{2n+4}. We confirm at the non-perturbative level the non-renormalization theorems for MHV F^{2n+2} terms that are expected to receive perturbative corrections only at n-loops. We compute also the one and two-loop corrections to the D^4F^4 term and show that its completion under SL(2,Z) duality is consistent with the one-instanton results.

### 12.11.2013 (Tuesday)

#### Leverhulme lecture: Unoriented quiver theories with flavor

Exceptional Seminar Massimo Bianchi (INFN)

 at: 14:00 QMWroom Room 208 abstract:

### 13.02.2013 (Wednesday)

#### Instantons in Field Theory and String Theory -- Leverhulme Lectures

Exceptional Seminar Massimo Bianchi ()

 at: 16:00 QMWroom 208 abstract: QMUL Graduate Lectures

### 06.02.2013 (Wednesday)

#### Instantons in Field Theory and String Theory -- Leverhulme Lectures

Exceptional Seminar Massimo Bianchi ()

 at: 16:00 QMWroom 208 abstract: QMUL Graduate Lectures

### 30.01.2013 (Wednesday)

#### Instantons in Field Theory and String Theory -- Leverhulme Lectures

Exceptional Seminar Massimo Bianchi ()

 at: 16:00 QMWroom 208 abstract: QMUL Graduate Lectures

### 21.11.2012 (Wednesday)

#### The Heterotic counterpart of D-brane recombination

Regular Seminar Massimo Bianchi (Roma Tor Vergata and Imperial)

 at: 13:15 KCLroom S4.23 abstract:

### 11.03.2010 (Thursday)

#### Pair production of small black holes in heterotic string theories

Regular Seminar Massimo Bianchi (Rome Tor Vergata)

 at: 14:00 QMWroom E303 Queens Building abstract: After reviewing how small BPS black holes with two charges can be described in perturbative Heterotic strings, we compute the cross section for their pair production at tree level and analyze angular and energy distributions. We consider both toroidal compactifications and FHSV orbifold model, and comment on scenari with large extra dimensions. Finally we briefly discuss how to extend our results to non-BPS, non-extremal and rotating BH's.