Date and time: April 5th @16:00 (CEST)

Speaker: Laura Lopez-Honorez (Université Libre de Bruxelles)

Title:  Freeze-in, SuperWIMPs and Primordial Black holes as possible sources of Non-cold dark matter.

Abstract:  Dark matter (DM) represents 80% of the matter budget of the Universe and up until now its nature is unknown. Even if the DM would interact very feebly with the SM, even gravitationally only, it could leave a distinctive imprint on cosmology observables due to free-streaming at early times. In my talk in particular I will discuss the case of DM arising from Freeze-in and superWIMP production mechanisms as well as primordial black hole evaporation. I will detail how in the later cases one can easily recast existing constraints from Lyman-alpha forest observations on thermal warm dark matter into those (non thermal) Non Cold DM scenarios, and discuss the complementarity between such a bound with other particle physics or cosmology constraints.

Slides: files/HiDDen-LLH.pdf

Time and date: Tuesday December 1st @ 16:00 (CET)

Speaker: Julia Harz (TUM)

Title: Constraining lepton-number violating interactions in rare kaon decays.

Abstract: The nature of neutrinos and especially the origin of their masses are crucial open questions in particle physics. If neutrinos are of Majorana type, lepton-number violating (LNV) interactions areexpected. In this context, neutrinoless double beta decay is considered to be the most sensitive probe, however, it is sensitive to LNV interactions among first generation fermions only. I will
discuss the possibility to constrain lepton-number violating operators with the rare kaon decay K→πνν. Within the Standard Model effective field theory with only light active Majorana neutrinos, I will present limits on the scale of new physics based on the results of the past E949 experiment as well as on the currently operating experiments NA62 and KOTO. I will discuss the specific signature of scalar currents in K→πνν arising from the LNV nature of the operators and their implications on the experimental sensitivity, stressing the need for dedicated searches for beyond the SM currents.

Slides: files/Hidden2020_-Julia-Harz-TUM.pdf


Time and date: Tuesday November 17th @ 16:00 (CET)

Speaker: Juraj Klaric (EPFL)

Title: Uniting low-scale leptogeneses

Abstract: The origin of the light neutrino masses and the baryon asymmetry of the Universe remain some of the biggest open questions of particle physics. Both of these problems can be solved if we extend the standard model by two right-handed neutrinos. The light neutrino masses can be generated through the type-I seesaw mechanism, and the baryon asymmetry of the Universe through leptogenesis. In this talk we will demonstrate that what was previously considered as different mechanisms of baryon asymmetry generation involving two right-handed Majorana neutrinos with masses far below the GUT scale— leptogenesis via neutrino oscillations and resonant leptogenesis—are actually united. We show that the observed baryon asymmetry can be generated for all experimentally allowed values of the right-handed neutrino masses above M ~100 MeV. We will also show that leptogenesis is effective in a broad range of the parameters, including mass splitting between two right-handed neutrinos as big as ∆M/M ∼0.1, as well as mixing angles between the heavy and light neutrinos large enough to be accessible to planned intensity experiments or future colliders.

Slides: files/UnitingLeptogneses.pdf


Date and time: Tuesday 31st May @16:00 (CEST)

Speaker:  Ennio Salvioni (CERN & Padua U.)

Title: Gegenbauer Goldstones

Abstract: I will discuss a new class of potentials for pseudo Nambu-Goldstone bosons (pNGBs) arising from the spontaneous breaking of a non-Abelian SO(N) global symmetry. These potentials take the form of Gegenbauer polynomials and are radiatively stable. I will use them to build new pNGB Higgs scenarios, “Gegenbauer Higgs” and “Gegenbauer’s Twin”, that can significantly reduce the fine-tuning compared to previous constructions. In particular, the second model can realize fully natural electroweak symmetry breaking consistently with current LHC measurements, and predicts large corrections to the Higgs cubic coupling that may be observed at the High-Luminosity phase of the LHC.

Slides: files/Ennio_Salvioni_Talk_HiddeN.pdf

Date and time: May 3rd @16:00 (CEST)

Speaker: Martin Bauer (IPPP & Durham University)

Title: ALP searches with Flavour and Collider observables.

Abstract:  Pseudo Nambu Goldstone bosons or axionlike particles (ALPs) can be light remnants of a heavy new physics sector.

The UV structure of this sector determines the coupling structure of the ALPs. Light ALPs are strongly constrained from beam-dump searches and astrophysical observables and ALPs with masses close to the electroweak scale can be discovered with resonance searches.

I will discuss different techniques to discover ALPs in the intermediate mass range with a special focus on long-lived ALPs.  Flavour observables can be particularly relevant in this mass region and I will discuss the RGE running of ALP couplings from the UV scale to the low energy scale to show how flavor violating couplings are generated.


Date and time: Tuesday,  February 15th @16:00 (CET)

Speaker: Tracy Slatyer (Massachusetts Institute of Technology)

Title: Thermal Squeezeout for Strongly Interacting Dark Matter

Abstract:  I will discuss the potential importance of a dark-sector phase transition in the early universe in setting the measured relic abundance, for a simple model of strongly interacting dark matter. Enhancement of the dark matter density within shrinking pockets of the high-temperature phase leads to a dramatic reduction in the late-time dark matter abundance, allowing for much heavier dark matter than in the standard thermal freezeout scenario.

Slides: files/Squeezeout_HiDDeN_Feb2022_Slatyer.pdf

Date and time: Tuesday,  January 11th @16:00 (CET)

Speaker: Zahra Tabrizi (Northwestern U.)

Title: EFT at FASERv: An experiment to probe them all.

Abstract: We will discuss how to systematically study physics beyond the standard model (BSM) in the neutrino experiments within the Standard Model Effective Field Theory (SMEFT) framework. In this way, the analysis of the data can capture large classes of models, where the new degrees of freedom have masses well above the relevant energy of the experiment. Moreover, it allows us to compare several experiments in a unified framework and in a systematic way. Our proposed approach could be applied to several short- and long baseline neutrino experiments. We will show the results of this approach at the FASERv experiment, which will be soon installed 480 m downstream of the ATLAS interaction point. For some coupling structures, we find that these neutrino detectors will be able to constrain interactions that are almost three orders of magnitude weaker than the Standard Model weak interactions, implying that they will be indirectly probing new physics at the 10 TeV scale.

Slides: files/HiDDeNJan2022.pdf

Date and time: Tuesday,  December 14th @16:00 (CET)

Speaker: Mikhail Shaposhnikov, EPFL Lausanne

Title: Quantum field theories without infinities and naturalness

Abstract: The standard way to do computations in Quantum Field Theory (QFT) is plagued by infinities and fine-tunings leading to the conception of "naturalness", which requires the cancellation of quadratic divergences by new particles with masses right above the Fermi scale. At the same time, the ultimate outcome of any QFT (the Standard Model in particular) is the prediction of all kinds of finite particle cross-sections in terms of a few finite input parameters (such as the mass of an electron and fine-structure constant in quantum electrodynamics). In this talk, I will describe how to relate the parameters of the theory to observables without running into divergences in Feynman diagrams. The existence of such a technique suggests that the "hierarchy problem" is not really physical, but rather an artifact of the conventional procedure of renormalisation of QFTs.

Slides: files/HiDDen_-Mikhail-Shaposhnikov.pdf


Date and time: Tuesday, November 30th @16:00 (CET)

Speaker: Daniele Teresi, CERN

Title: Sliding Naturalness

Abstract: I will present a novel framework to solve simultaneously the electroweak hierarchy problem and the strong-CP problem. A small but finite Higgs vacuum expectation value and a small \thetaθ-angle are selected after the QCD phase transition, without relying on the Peccei-Quinn mechanism or other traditional solutions. This novel solution predicts a distinctive pattern of correlated signals at hadronic EDM, fuzzy dark matter and axion experiments. I will then discuss other incarnations of the mechanism in more generality, with different phenomenology, and attempt to draw a (relatively) unified picture of cosmological approaches to the Higgs hierarchy problem.

Slides: files/Hidden--Daniele-Teresi-CERN.pdf


Date and time: Tuesday November 16th @16:00 (CET)

Speaker: Josef Pradler, Institute of High Energy Physics, Vienna, Austria

Title: The sunny side of dark matter direct detection

Abstract: The direct detection of light dark matter particles that are gravitationally bound to the galaxy represent an experimental challenge as their kinetic energy can fall below the energy scale for generating a visible signal, typically at the order of eV. In this talk I will review the idea that there is an irreducible contribution to the flux that got accelerated in the solar interior to keV energies, opening up the prospects of probing MeV-scale DM masses with the largest and cleanest direct detection constraints such as XENON1T.

Slides: files/2021HiddenWebinarPradler.pdf


Date and time: Tuesday, November 2nd @16:00 (CET)

Speaker: Vedran Brdar, Fermilab and Northwester U.

Title: Energy-Dependent Neutrino Mixing Parameters at Oscillation Experiments.

Abstract: One of the most important achievements in the field of particle physics was the discovery of neutrino oscillations. Despite already awarded Nobel Prize, neutrino oscillation experiments still have a lot to offer, primarily the discovery of CP violation in the lepton sector is anticipated. The expression for neutrino oscillation probabilities is composed of neutrino mixing parameters and mass squared differences. In this seminar, we argue that mixing parameters at the scale of neutrino production and detection do not necessarily need to coincide since such parameters are subject to renormalization group evolution and the two processes occur at different energies.

We discuss this in the frame of a particular UV compete realization and demonstrate that quantum effects can yield relevant observable effects at various neutrino experiments. As an example, we consider high-energy astrophysical neutrinos at IceCube and show that neutron decay production mechanism that is considered to be strongly disfavored by present data becomes viable if significant renormalization group effects are present. We also scrutinize terrestrial experiments and show that the mismatch between neutrino parameters at production and detection can induce large effects at T2K and NOvA.

Slides: files/Vedran.pdf


Date and time: Tuesday, October 19th at 16:00 CET

Speaker: Mark Ross-Lonergan, Columbia University

Title: Search for anomalous single-photon production in MicroBooNE as a first test of the MiniBooNE low-energy excess.

Abstract: We report first results from a search for neutrino-induced neutral current (NC) resonant ∆(1232) baryon production followed by ∆ radiative decay. Data corresponding to MicroBooNE’s first three years of operations (6.80×1020protons on target) are used to select single-photon events with one or zero protons and without charged leptons in the final state. The background is constrained via an in-situ high-purity measurement of NC π0 events. This provides the world’s most sensitive search for NC Delta→Ngamma below 1 GeV, and a first test of the MiniBooNE low-energy excess under a single photon hypothesis.

Slides: files/HiDDENS_Webinar_Oct19_markrosslonergan.pdf


Date and time: Tuesday, October 5th at 16:00 CET

Speaker:  Ilaria Brivio (Heidelberg University)

Title: The Neutrino Option

Abstract: The core idea of the Neutrino Option is that the Higgs potential of the SM could be naturally generated by loops of right-handed neutrinos, starting from a nearly-conformal condition in a very minimal type-I seesaw model. After introducing the generalities of this framework, I will discuss its compatibility with leptogenesis and I will give an overview of the plausible UV completions.

Slides: files/slides_HIDDeN_-I-Brivio.pdf


Date and time: Tuesday, June 8th at 16:00 CET

Speaker:  Gregorio Herdoiza (Institute for Theoretical Physics (IFT) UAM-CSIC)

Title: Hadronic contributions to the muon g-2

Abstract: The calculation of the anomalous magnetic moment of the muon involve sizable contributions from hadronic physics, whose uncertainties dominate the total error of the Standard Model prediction. In this talk, I will present the current status of the computations of these effects, based on data-driven dispersive methods and on lattice QCD+QED simulations. I will also indicate some of the ongoing consistency checks of these methods, and their prospects, aiming at consolidating the Standard Model result in view of the upcoming muon g-2 measurement updates by the Fermilab experiment.

Slides: files/herdoiza_hidden.pdf



Date and time: Tuesday, April 27th at 16:00 CET

Speaker:  Andreas Crivellin (CERN & University of Zurich & Paul Scherrer Institut)

Title: Discovering Lepton Flavour Universality Violating New Physics

Abstract: While the LHC has not discovered any new particles directly yet, hints for the violation of lepton flavour universality  (satisfied within the SM) accumulated in recent years. In particular, deviations from the SM predictions were observed in semi-leptonic B decays (b->sll and b->ctau), in the anomalous magnetic moment of the muon (g-2), in leptonic tau decays and di-electron searches. Furthermore, also the deficit in first row CKM unitarity, known as the Cabibbo Angle Anomaly, can be interpreted as a sign of lepton flavour universality violation. In this talk I review the status of these anomalies and give an overview of the possible interpretations in terms of new physics models. 

Slides: files/Madrid2021_-Andreas-Crivellin.pdf



Date and time: Tuesday, April 13th at 16:00 CET

Speaker:  Jorge Martin Camalich (Instituto de Astrofísica de Canarias)

Title: Implications of the new measurements of  b → sµµ decays

Abstract: I will give an overview of the current status of discrepancies with the SM that appear in  b > s mumu decays and which would imply a breakdown of lepton universality in nature. In particular, I will describe the implications of the new measurements of RK and Bq > mumu.

Slides: files/talkCamalich.pdf



Date and time: Tuesday, March 30th at 16:00 CET

Speaker:  Rick. S. Gupta (IPPP Durham)

Title: A heavy axion 'massless up' from partial compositeness

Abstract: We show that QCD instantons can generate large effects at small length scales in the ultraviolet in standard composite Higgs models that utilise partial compositeness. This has important implications for possible solutions of the strong CP problem in these models. First, we show that in the simplest known UV completions of composite Higgs models, if an axion is also present, it can have a mass much larger than the usual QCD axion. Even more remarkable is the case where there are no axions, but the strong CP problem can be solved by generating the up-quark mass entirely from the contribution of instantons thus reviving the massless up-quark solution for these models. In both cases no additional field content is required apart from what is required to realize partial compositeness.

Slides: files/Hidden-ITN-seminar_gupta.pdf



Date and time: Tuesday, March 16th at 16:00 CET

Speaker:  Jeff Dror (UC Santa Cruz)

Title: The Cosmic Axion Background

Abstract: Existing searches for cosmic axions relics have relied heavily on the axion being non-relativistic and making up dark matter. However, light axions can be copiously produced in the early Universe and remain relativistic today, thereby constituting a Cosmic axion Background (CaB).  In this talk I will discuss the production and detection of a CaB. Prototypical examples of axion sources are thermal production, dark-matter decay, parametric resonance, and topological defect decay. Each of these has a characteristic frequency spectrum that can be searched for in axion direct detection experiments. I will focus on the axion-photon coupling and study the sensitivity of current and future versions of ADMX, HAYSTAC, DMRadio, and ABRACADABRA to a CaB, finding that the data collected in search of dark matter can be repurposed to detect axion energy densities below limits set by measurements of the energy budget of the Universe. In this way, direct detection of relativistic relics offers a powerful new opportunity to learn about the early Universe and, potentially, discover the axion.

Slides: files/SeminarTalk_HiDDeN_Jeff_Dror.pdf



Date and time: Tuesday, March 2nd at 16:00 CET

Speaker:  Tongyan Lin (UC San Diego)

Title: Dark matter scattering in dielectrics

Abstract: Direct detection experiments are rapidly advancing in the search for sub-GeV dark matter. As energy thresholds become lower, the many-body physics of a target material becomes increasingly important to understand in determining the dark matter signal. In this talk, I will show how dark matter scattering in dielectric materials can be understood in terms of the dielectric response. This provides both a useful conceptual framing, and also allows us to calculate several new effects. I will then discuss two applications: screening effects for dark matter electron scattering, and the Migdal effect in semiconductors.

Slides: files/2021_03_02_Tongyan-Lin.pdf



Date and time: Tuesday, February 16th at 16:00 CET

Speaker:  Jordi Salvado (Universidad de Barcelona)

Title: Long Range Interactions in Cosmology: Implications for Neutrinos

Abstract: Cosmology is well suited to study the effects of long range interactions due to the large densities in the early Universe. In this talk, we explore how the energy density and equation of state of a fermion system diverge from the commonly assumed ideal gas form under the presence of scalar long range interactions with a range much smaller than cosmological scales. In this scenario, “small”-scale physics can impact our largest-scale observations. As a benchmark, we apply the formalism to self-interacting neutrinos, performing an analysis to present and future cosmological data. Our results show that the current cosmological neutrino mass bound is fully avoided in the presence of a long range interaction, opening the possibility for a laboratory neutrino mass detection in the near future. We also demonstrate an interesting complementarity between neutrino laboratory experiments and the future EUCLID survey.

Slides: files/Long-Range-cosmo-nus.pdf



Time and date:  Tuesday, February 2nd @ 16:00 (CET)

Speaker: Matheus Hostert (University of Minnesota & Perimeter Institute)

Title: A Dark Seesaw at Low Energy Experiments

Abstract: Generic dark sectors can have a rich interplay with the origin of neutrino masses. In this talk, I will discuss an example, where heavy neutrinos in a low-scale seesaw are part of a secluded U(1)' sector. The interplay between the dark photon, heavy neutrinos, and scalars leads to a set of unexplored signatures in neutrino scattering, e+e− colliders, and kaon decay experiments. I will highlight applications of a renormalizable model to low-energy anomalies, including MiniBooNE and the (g-2) of the muon.

Slides: files/hidden_mhostert.pdf 



Time and date:  Tuesday January 19th @ 16:00 (CET)

Speaker: Gilly Elor (University of Washington)

Title: Making the Universe at 20 MeV

Abstract: We present a testable mechanism of low-scale baryogenesis and dark matter production in which neither baryon nor lepton number are violated. Charged D mesons are produced out-of-equilibrium at tens of MeV temperatures. The D mesons quickly undergo CP-violating decays to charged pions, which then decay into dark-sector leptons without violating lepton number. To transfer this lepton asymmetry to the baryon asymmetry, the dark leptons scatter on additional dark-sector states charged under lepton and baryon number. Amusingly, this transfer proceeds without electroweak sphalerons, which are no longer active at such low scales. We present two example models which can achieve this transfer while remaining consistent with current limits. The required amount of CP violation in charged D meson decays, while currently allowed, will be probed by colliders. Additionally, the relevant decays of charged pions to dark-sector leptons have been constrained by the PIENU experiment and will be further explored in upcoming experiments.

Slides: soon



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