IJS-FMF high-energy physics seminars

1 May 2020, 08:00 → 31 Jan 2021, 18:00 Europe/Ljubljana

https://fmf-uni-lj-si.zoom.us/j/3601731049?pwd=bVNQRjUxU2ExZ0cveWcxYXNUUGdjZz09 (Department of Theoretical Physics, Jožef Stefan Institute)

Weekly seminars organized by the "Theory of nuclei, elementary particles, and fields" group at the Jožef Stefan Institute (IJS) and Faculty of Mathematics and Physics, University of Ljubljana.

The webinar Zoom link is

https://fmf-uni-lj-si.zoom.us/j/3601731049?pwd=bVNQRjUxU2ExZ0cveWcxYXNUUGdjZz09

Tuesday 26 May

Tuesday/Thursday seminars

1 Electroweak baryogenesis at high bubble wall velocities

https://zoom.us/j/97158916531

Speaker: Prof. James Cline (McGill)

Slides Cline_fastwall2.mp4 Cline_Fastwall2.pdf

Tuesday 2 June

Tuesday/Thursday seminars

2 How long does the hydrogen atom live?

Speaker: David McKeen (TRIUMPH)

Slides mckeen.pdf video.mp4

Thursday 11 June

Tuesday/Thursday seminars

3 Nu cosmologies and signals

In this talk I will present some new signals of well-motivated UV completions of the Standard Model. Firstly, I will survey the cosmology of minimal left-right extensions of the Standard Model. Such theories have two possible mechanisms to set their relic density and we study each of them in general. Surprisingly, the viable mechanisms responsible for setting the dark matter density are predictive and can be probed by current and near-future experiments. Secondly (time-pending), I will go over how leptogenesis through the see-saw mechanism can be detected using gravitational waves. I will show how a restored high scale symmetry is necessary for a natural formulation of the see-saw mechanism and such symmetries often predict a background of gravitational waves. This background can be seen with projections for future experiments, potentially probing the entire range relevant of symmetry-breaking scales relevant for leptogenesis.

Speaker: Jeff Dror (Berkeley)

Slides SeminarTalk.pdf Video recording

Tuesday 16 June

Tuesday/Thursday seminars

4 Model-independent energy budget of cosmological first-order phase transitions

We study the energy budget of a first-order cosmological phase transition, which is an important factor in the prediction of the resulting gravitational wave spectrum. Formerly, this analysis was based mostly on simplified models as for example the bag equation of state. Here, we present a model-independent approach that is exact up to the temperature dependence of the speed of sound in the broken phase. We find that the only relevant quantities that enter in the hydrodynamic analysis are the speed of sound in the broken phase and a linear combination of the energy and pressure differences between the two phases which we call pseudotrace (normalized to the enthalpy in the broken phase). The pseudotrace quantifies the strength of the phase transition and yields the conventional trace of the energy-momentum tensor for a relativistic plasma (with speed of sound squared of one third). We study this approach in several realistic models of the phase transition and also provide a code snippet that can be used to determine the efficiency coefficient for a given phase transition strength and speed of sound. It turns out that our approach is accurate to the percent level for moderately strong phase transitions, while former approaches give at best the right order of magnitude.

Speaker: Thomas Konstandin (DESY)

Slides seminar.pdf Video recording

Tuesday 23 June

Tuesday/Thursday seminars

5 The Dark Side of 4321

The evidence of Dark Matter (DM) is one of the strongest observational arguments in favor of physics beyond the Standard Model. Despite expectations, a similar evidence has been lacking so far in collider searches, with the possible exception of B-physics discrepancies, a coherent set of persistent deviations in a homogeneous dataset consisting of b → c and b → s semi-leptonic transitions. We explore the question whether DM and the B discrepancies may have a common origin. We do so in the context of the so-called 4321 gauge model, a UV-complete and calculable setup that yields a U1 leptoquark, the by far most successful single mediator able to explain the B anomalies, along with other new gauge bosons, including a Z'. Adding to this setup a 'minimal' DM fermionic multiplet, consisting of a *4* under the 4321's SU(4), we find the resulting model in natural agreement with the relic-density observation and with the most severe direct-detection bounds, in the sense that the parameter space selected by B physics is also the one favored by DM phenomenology. The DM candidate is a particle with a mass in the WIMP range, freeze-out dynamics includes a co-annihilator (the 'rest' of the *4* multiplet), and the most important gauge mediator in the DM sector is the Z'.

Speaker: Diego Guadagnoli

Thursday 2 July

Tuesday/Thursday seminars

6 Phase Transitions and gravitational waves

Speaker: Marek Lewicky (KCL, Warsaw U.)

Slides MLewicki_EnergyBudgetTalk.pdf Video recording

Tuesday 7 July

Tuesday/Thursday seminars

7 Electroweak Baryogenesis, ACME II and Dark Sector CP Violation

Speaker: Prof. Yue Zhang (Carleton University)

Slides JSI_HET_Seminar_2020.pdf Video recording

Thursday 9 July

Tuesday/Thursday seminars

8 The dark side of 4321

Speaker: Dr Diego Guadagnoli (Annecy)

Slides Talk_Ljubljana_Guadagnoli.pdf Video recording

Thursday 17 September

Tuesday/Thursday seminars

9 Baryon and lepton number intricacies in axion models

Because the axion symmetry has to be anomalous to solve the strong CP puzzle, some colored and chiral fermions have to transform non-trivially under this symmetry. But when the SM fermions are charged, as in the PQ or DFSZ models, this symmetry ends up entangled with the SM global symmetries, baryon (B) and lepton (L) numbers. This raises several questions addressed in this talk. First, this entanglement will be described in details, showing how it induces some ambiguities in the PQ charges of the fermions, but that those ambiguities have no phenomenological impact. Then, the compatibility of axion models with some explicit B and/or L violating effects will be analyzed, including those arising from seesaw mechanisms, electroweak instanton interactions, or explicit B and L violating effective operators. At that stage, we will also quantify how many of these effects can be simultaneously present, and discuss the consequences for the axion mass and vacuum alignment if too many of them are introduced. In this way, large classes of B and/or L violating interactions leaving the axion phenomenology totally intact, thus undistinguishable, can be identified, like for example the various implementations of the type I and II seesaw mechanisms in the DFSZ context. Based on 1903.12559, 2006.06778.

Speaker: Dr Christopher Smith (LPSC, Grenoble)

Slides Slides_Smith_Sep2020.pdf Video recording

Thursday 8 October

Tuesday/Thursday seminars

10 Crunching Dilaton, Hidden Naturalness

We introduce a new approach to the Higgs naturalness problem, where the value of the Higgs mass is tied to cosmic stability and the possibility of a large observable Universe. The Higgs mixes with the dilaton of a CFT sector whose true ground state has a large negative vacuum energy. If the Higgs VEV is non-zero and below O(TeV), the CFT also admits a second metastable vacuum, where the expansion history of the Universe is conventional. As a result, only Hubble patches with unnaturally small values of the Higgs mass support inflation and post-inflationary expansion, while all other patches rapidly crunch. The elementary Higgs VEV driving the dilaton potential is the essence of our new solution to the hierarchy problem. The main experimental prediction is a light dilaton field in the 0.1-10 GeV range that mixes with the Higgs. Part of the viable parameter space has already been probed by measurements of rare B-meson decays, and the rest will be fully explored by future colliders and experiments searching for light, weakly-coupled particles.

Speaker: Dr Raffaele Tito D'Agnolo (IPHT)

Slides Video recording

Thursday 15 October

Tuesday/Thursday seminars

11 The Neutrino Magnetic Moment Portal: Cosmology, Astrophysics, and Direct Detection

We revisit the physics of neutrino magnetic moments, focusing in particular on the case where the right-handed, or sterile, neutrinos are heavier (up to several MeV) than the left-handed Standard Model neutrinos. The discussion is centered around the idea of detecting an upscattering event mediated by a transition magnetic moment in a neutrino or dark matter experiment. Considering neutrinos from all known sources, as well as including all available data from XENON1T and Borexino, we derive the strongest up-to-date exclusion limits on the active-to-sterile neutrino transition magnetic moment. We then study complementary constraints from astrophysics and cosmology, performing, in particular, a thorough analysis of BBN. We find that these data sets scrutinize most of the relevant parameter space. Explaining the XENON1T excess with transition magnetic moments is marginally possible if conservative assumptions are adopted regarding the supernova 1987A and CMB constraints. Finally, we discuss model-building challenges that arise in scenarios that feature large magnetic moments while keeping neutrino masses well below 1 eV. We present a successful ultraviolet-complete model of this type based on TeV-scale leptoquarks, establishing links with muon magnetic moment, B physics anomalies, and collider searches at the LHC.

Speaker: Dr Admir Greljo (CERN)

Slides IJS_GreljoAdmir.pdf IJS_Greljo.mp4

Wednesday 21 October

High energy group meeting 2020

Given the epidemic situation and government restrictions, we are hosting a series of presentations of PhD students and postdocs online.

12 Enhanced CP asymmetries in B -> K mu mu

Speaker: Aleks Smolkovič (IJS)

Slides resonantcp.pdf

13 Long-Lived Particles at Belle II and GAZELLE

Speaker: Dr Michele Tammaro (IJS)

Slides Tammaro_Belica20.pdf

14 An exact false vacuum decay rate

Speaker: Victor Guada (IJS)

Slides False_Vacuum_Decay_IJS_2020.pdf

12:00 Lunch break

High energy group meeting 2020: High energy group meeting

Given the epidemic situation and government restrictions, we are hosting a series of presentations of PhD students and postdocs online.

15 J/\psi-nucleon scattering in P_c^+ pentaquark channels

Speaker: Urša Skerbiš Štok (IJS)

Slides Skerbis_Stok_Jpsi_proton_one_channel.pdf

16 New Physics in Missing ET + bjet experiments

Speaker: Arman Korajac (IJS)

Slides arman_prezentacija.pdf

17 Z_b tetraquark channel with lattice QCD

Speaker: Mitja Šadl (IJS)

Slides mitja_sadl.pdf

Thursday 29 October

Tuesday/Thursday seminars

Thursday 14 January

Tuesday/Thursday seminars