# High Energy Theory Seminars.

These seminars take place every Wednesday at 15:00 in Room S.

High Energy Theory seminars are one-hour research seminars dedicated to high energy physics, cosmology and astrophysics, with a special emphasis on particle physics (PH, light gray) or string theory (TH, dark gray). Seminars intended for the whole group are marked in light yellow.

The organizers of the String Theory seminars (TH) are L. Martucci and S. Giusto. The organizers of the Particle Physics Phenomenology seminars (PH) are P. Mastrolia and P. Paradisi.

Sometimes we also host some special events, like workshops and conferences. These are highlighted in light blue.

You can click on the titles to see the slides of the talk.

### 2019/2020 Calendar PRINT

Date | Speaker (Affiliation) |
Title | Room &Time |

09-10-19 Wednesday | Stefano Di Vita INFN MIlan | Differential equations and iterated integrals for massive multi-loop Feynman integrals Abstract In this talk I will give an overview of the differential equations method for the calculation of multiloop Feynman diagrams, which we recently applied to several cases where massive legs and propagators are present. I will discuss how the systems of differential equations arise, how they are brought in canonical form with the help of the Magnus exponential, what functions can be used to give a closed-form representation of the solution, and how they are analytically continued to the kinematic regions of interest. Some examples will be given, such as the master integrals for the NNLO QED corrections to mu-e scattering, which are crucial for the physics program of MUonE, an experiment proposed with the goal of determining the leading hadronic contribution to the muon g-2 in a novel way. | Aula Voci 14:00 |

23-10-19 Wednesday | Kei Yamamoto Univ. Zurich | B-physics anomaly and SM flavor hierarchies Abstract The observed hierarchies in the Standard Model(SM) Yukawas represent one of the most interesting open problems. On the other hand, LHC, Belle and BABAR experiments have reported the test of lepton flavor universality in B-meson decays which seem to indicate a coherent pattern of deviations from the SM predictions. In this talk, I will review these hints and discuss the implications derived from effective field theory approach based on U(2) flavor symmetry, and leptoquark models. | Aula Voci 15:00 |

30-10-19 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

6-11-19 Wednesday | David Marzocca INFN, Trieste | From B-anomalies to Kaon and precision physics Abstract In this talk I will review some new physics interpretations for the B-physics anomalies, and their implications for other flavor and precision observables. Regarding the neutral-current anomalies, I will describe the Rank-One Flavor Violation hypothesis and how the setup can be constrained with other B-meson and Kaon decays. I will then discuss a combined interpretation of both neutral- and charged-current anomalies, with a complete one-loop matching to the SM Effective Field Theory, and some preliminary results for flavor as well as electroweak precision observables. | Aula Voci 15:00 |

13-11-19 Wednesday | Anthony Charles KU Leuven | Euclidean Black Saddles and AdS4 Black Holes Abstract The entropy of a class of asymptotically-AdS4 black holes can be reproduced by the partition function of the dual ABJM theory via localization. However, establishing this match requires a particular extremization over field theory parameters. This begs the question: what are the bulk dual geometries when we do not extremize in the field theory? In this talk, I will show that these bulk duals are smooth Euclidean geometries with finitely-capped throats. These geometries generically have no clear interpretation in Lorentzian signature, but when their throat becomes infinitely long they become black holes with an AdS2 near-horizon geometry. For any set of field theory parameters whose extremization is compatible with a black hole, we find a large family of Euclidean geometries whose on-shell action reproduces the ABJM partition function exactly, without the need to extremize, thus establishing a more complete understanding of AdS4/CFT3 holography. | Aula Voci 15:00 |

20-11-19 Wednesday | Itamar Shamir SISSA | Defect anomalies and marginal couplings Abstract Conformal anomalies play a prominent role in the study of conformal field theories with important applications to RG flows. In the presence of a boundary (or more generally defects) new types of conformal anomalies appear which are localised on the defect. I will review the basic aspects of defects in conformal field theory and the motivation to study them, focusing mainly on new types conformal anomalies and their properties. I will show that unlike the standard conformal anomalies in the bulk, the defect anomalies can have non-trivial dependence on exactly marginal couplings. | Aula Voci 15:00 |

27-11-19 Wednesday | Luca Di Luzio Pisa U. | Rethinking the QCD axion Abstract Four decades after its prediction the axion remains the most compelling solution to the strong CP problem and a well motivated dark matter candidate, inspiring several ultrasensitive experiments based on axion-photon mixing. After reviewing the axion solution of the strong CP problem and the experimental landscape of axion searches, I will focus on some recent developments in axion model building which show that the QCD axion parameter space is much larger than what traditionally thought. The implications for astrophysical limits and future experiments will be discussed as well. | Aula Voci 15:00 |

04-12-19 Wednesday | Alexander Mitov Cambridge U. | Latest developments in NNLO calculations for 2-to-3 LHC processes Abstract There are two parallel lines of development in perturbative QCD: phenomenological predictions for high-precision LHC observables (typically in NNLO) and the calculation of multi-loop scattering amplitudes. These two research directions are not independent, however, since the corresponding two-loop amplitude is an essential ingredient to any NNLO calculation. I will review the recent progress in both scattering amplitudes and NNLO calculations and, as an example of their cross-talk, will present the first 2-to-3 NNLO calculation: 3 photon production at the LHC. The talk should be of interest to both formal and pheno-oriented theorists as well as experimentalists since it will lay out the deep interconnection between branches of theoretical particle physics and LHC measurements. | Aula Voci 15:00 |

11-12-19 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

16-12-19 Monday | Konstantinos Papadopoulos NCSR-DEMOKRITOS | Recent progress on two-loop massless pentabox integrals with one off-shell leg Abstract In the last decade we had the chance to witness some very important and long-awaited discoveries in physics such as the identification of the Higgs particle, the detection of the gravitational waves and the first image of a BH horizon. In all cases very sophisticated experimental instruments were used along with robust theoretical predictions in order to reveal underlying tiny signals that made these discoveries possible. In particle physics, higher-order perturbative corrections to scattering amplitudes proved important in exploiting the LHC data. Next-to-leading order accuracy is the nowadays theory standard. Nevertheless, in order to fully exploit the coming LHC high-luminosity data and even more so, the potential of the Future Circular Collider (FCC), we need to go beyond NLO. In this talk I will review the recent progress in NNLO perturbative calculations with emphasis to two-loop amplitude reduction and to the analytic computation of the Master Integrals involved. I will also report on the most recent results on non-planar five-point two-loop Master Integrals family with one off shell external particle (arXiv:1910.06275). | Aula Voci 15:00 |

18-12-19 Wednesday | Various speakers | MathemAmplitudes 2019 Abstract | Archivio Antico 9:00 |

19-12-19 Thursday | Various speakers | MathemAmplitudes 2019 Abstract | Aula Rosino 9:00 |

20-12-19 Friday | Various speakers | MathemAmplitudes 2019 Abstract | Aula Rosino 9:00 |

08-01-20 Wednesday | Federico Bonetti Johns Hopkins U. | Anomaly inflow, geometric engineering, and holography Abstract A large class of 4d SCFTs can be engineered by wrapping a stack of M5-branes on a compact space, possibly with defects. ‘t Hooft anomalies are crucial observables for such theories, which often do not admit any known Lagrangian description. Building on the seminal work of Freed, Harvey, Minasian, Moore, we develop systematic tools for extracting the ‘t Hooft anomalies of a geometrically engineered 4d theory using anomaly inflow from the M-theory bulk. We exemplify our tools by studying a class of setups with M5-branes probing a C^2/Z_2 singularity. We argue that these setups define 4d SCFTs which are dual to a class of AdS_5 solutions—first discussed by Gauntlett, Martelli, Sparks, Waldram—whose field theory interpretation has been a longstanding puzzle. | Aula Voci 15:00 |

15-01-20 Wednesday | Joachim Kopp CERN | "Hot" Topics in Astroparticle Physics - Finite Temperature Effects in Dark Matter Phenomenology Abstract We discuss the possible impact of thermal quantum field theory effects - in particular phase transitions - on the phenomenology of dark matter. After reviewing the physics of phase transitions in general, we discuss the electroweak phase transition in the early Universe, and we show how this transition can be modified in theories featuring more than one Higgs boson. We then argue that the observed abundance of dark matter today may have been determined by the dynamics of the electroweak phase transitions, rather than by conventional thermal freeze-out. We conclude by outlining possible tests of this hypothesis at the LHC and elsewhere. | Aula Voci 15:00 |

22-01-20 Wednesday | Pedro F. Ramirez AEI, Potsdam | Stringy extremal black holes Abstract In the context of string theory, classical black hole solutions to the standard theories of supergravity receive corrections due to the presence of higher-derivative terms in the effective perturbative expansion. These corrections generically modify the physical properties of the solution and affect the allowed region of parameter space. I will review recent advances in the field for the case of extremal black holes (supersymmetric and not supersymmetric) of heterotic string theory, where the analytical resolution of the problem is feasible. In particular, I will describe the implications of our results in the context of the weak gravity conjecture, as the charge-to-mass ratio of extremal black holes is sometimes modified. Likewise, I will describe how the entropy, charges and mass are generically modified and emphasize the importance of properly taking into account such modification, discussing the implications for the so-called 'small black holes'. | Aula Voci 15:00 |

29-01-20 Wednesday | Alessandro Vicini Milan U. | Precision tests of the SM at the LHC and at future colliders Abstract I will review the high-precision determination of the EW parameters at the LHC and the perspectives offered by future colliders. Several recent technical developments allow a promising determination of the W boson mass and of the weak mixing angle, even in the complex environment of a high-luminosity hadron collider. The impact on the precision tests of the Standard Model will be discussed. I will eventually comment on the extreme phenomenological challenges emerging in the elaboration of the physics program of future electron-positron colliders. | Aula Voci 15:00 |

04-02-20 Tuesday | Ivano Basile Scuola Normale | On Vacuum Stability without Supersymmetry: Brane dynamics, bubbles and holography Abstract In this talk I will present some recent results on instabilities of anti-de Sitter flux compactifications in effective field theories arising from non-supersymmetric string models, namely the USp(32) and U(32) orientifold models and the SO(16) x SO(16) heterotic string. We discuss perturbative and non-perturbative instabilities and frame the vacua in terms of brane stacks, analyzing their back-reacted geometry and reproducing AdS its near-horizon limit. Then we describe the instabilities as branes separating from the stack, computing the associated decay rate matching a probe brane computation with the semi-classical Coleman-de Luccia result. We conclude briefly discussing possible implications regarding the fate of unstable vacua in string theory beyond the semi-classical limit, connecting this scenario to holographic renormalization group flows and to a "de Sitter on a brane" construction that was outlined in the recent literature. | Aula Voci 14:00 |

12-02-20 Wednesday | Severin Lüst Ecole Polytechnique | Uplifting Runaways and the Tadpole Problem Abstract I will discuss a mechanism which can lead to a possible instability of the KKLT construction for de Sitter vacua. The sphere at the tip of a warped deformed conifold throat can be destabilized by antibranes placed in the throat. Consequently, the stabilization of moduli should not be treated independently from the antibrane uplift in KKLT-like scenarios. A similar bound can be found for numerically constructed Klebanov-Strassler black holes. I will furthermore comment on the mass scales and the effects on supersymmetry breaking in this setup. This conifold destabilization mechanism can be avoided by turning on a large amount of flux on the sphere, but tadpole cancelation constraints the hierarchy of scales in a type IIB flux compactification. Even though sufficiently large tadpole bounds can be realized in string theory, they always come at the expense of a large number of moduli. The stabilization of these moduli by fluxes contributes to the tadpole condition as well, reducing the maximal flux on the KS-throat.I will discuss this problem for the example of M-theory on K3 x K3. | Aula Voci 15:00 |

15-04-20 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

22-04-20 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

29-04-20 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

06-05-20 Wednesday | Chris Couzens ITP Utrecht | title (TBA) Abstract | Aula Voci 15:00 |

13-05-20 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

20-05-20 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

27-05-20 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

03-06-20 Wednesday | Pieter Bomans Leuven U. | title (TBA) Abstract | Aula Voci 15:00 |

10-06-20 Wednesday | speaker (TBA) affiliation (TBA) | title (TBA) Abstract | Aula Voci 15:00 |

### Links to Past Calendars

High energy theory seminars for the a.y. 2017/2018, 2016/2017, 2015/2016, 2014/2015, 2013/2014, 2012/2013, 2011/2012, 2010/2011, 2009/2010, 2008/2009, 2007/2008, 2006/2007, 2005/2006