Date and time: Monday December 14th at 11:00 CET
Speaker: Federica Pompa (UVEG ESR)
Title: Neutrino physics with the XENONnT experiment
Abstract: One of the most active fields in physics is the search for Dark Matter, for which the XENON Project is one of the main protagonists. The new XENONnT experiment, upgrade of the previous XENON1T, will be operative soon in the underground Laboratori Nazionali del Gran Sasso, in Italy. It is a multi-ton detector for direct search of Dark Matter, consisting of a double phase liquid-gas xenon Time Projection Chamber (TPC) containing about 6 tons of liquid xenon target mass. This TPC is enclosed into a Cryostat surrounded by two Veto systems instrumented with photomultiplier tubes (PMTs) for muon and neutron tagging. The whole setup is inserted into a tank containing Gd-doped water, to suppress further the background in the TPC. Its aim, as that of its precursor, is to detect WIMPs elastic scattering on xenon nuclei through the measure of the light and charge signals produced by recoils in liquid xenon.Thanks to the large masses of water and xenon used, the XENONnT potential can be extended also to a different topics of particle and astroparticle physics, in particular to test its capabilities to detect neutrinos coming from Supernova explosions and to observe the Standard Model forbidden neutrinoless double beta decay.I will present the results of a Monte Carlo simulation to predict the XENONnT detection efficiencies for Supernova neutrino events as inverse beta decay interactions in the neutron and muon Vetoes.Then I will investigate the XENONnT power to detect neutrinoless double beta decay of the Xe-136 isotope by evaluating the electronic recoil background rate from Cryostat and PMTs in the energy region where we expect to observe this nuclear transition.
Slides: files/HIDDeN_webinar_FP.pdf
Passcode: A=$0aVxS
Date and time: Monday, January 11th at 11:30 CET
Speaker: Gioacchino Piazza (CNRS ESR)
Title: Axion hot dark matter bound, reliably
Abstract: Axions originally emerged as low-energy remnants of the Peccei Quinn solution to the strong CP problem, but they also unavoidably contribute to the energy density of the Universe. The thermal axion population contributes to the effective number of extra relativistic degrees of freedom, whose value is constrained by cosmic microwave background (CMB) experiments.
In the talk I will discuss axion thermalization at temperatures below 150 MeV, where the main thermalization channel is the axion-pion scattering. Based on the leading order (LO) axion-pion chiral effective field theory (EFT), the highest attainable axion mass is approximately below the eV. However, this bound is found to be not reliable, since in a heat bath of 100 MeV the axion-pion scattering happens at center of mass energies above the validity of the 2-flavour chiral EFT.
To prove this, I will provide the full axion-pion thermalization rate to next-to-leading order, and show that the LO bound is indeed obtained by extrapolating the chiral expansion in a region of temperatures where the effective field theory breaks down.
Thus, in order to set targets for future CMB experiments, new strategies are required to obtain a reliable bound.
Slides: files/Webinar_Gioacchino-Piazza.pdf
Video: http://ific.uv.es/~omena/HIDDEN_ESR/110121/
Date and time: Monday January 24th @15:00 PM CET
Speaker: Salvador Rosauro ( CNRS ESR)
Title: Neutrino Electroweak Baryogenesis
Abstract: We investigate if the CP violation necessary for successful electroweak baryogenesis may be sourced by the neutrino Yukawa couplings. In particular, we consider an electroweak scale Seesaw realization with sizable Yukawas where the new neutrino singlets form (pseudo)-Dirac pairs, as in the linear or inverse Seesaw variants. We find that the baryon asymmetry obtained strongly depends on how the neutrino masses vary within the bubble walls. Moreover, we also find that flavour effects critically impact the final asymmetry obtained and that, taking them into account, the observed value may be obtained in some regions of the parameter space. This source of CP violation naturally avoids the strong constraints from electric dipole moments and links the origin of the baryon asymmetry of the Universe with the mechanism underlying neutrino masses. Interestingly, the mixing of the active and heavy neutrinos needs to be sizable and could be probed at the LHC or future collider experiments.
Date and time: Monday, December 20th at 11:00 AM CET.
Speaker: Xavier Ponce INFN ESR
Title: ΔEFT: an Effective Field Theory of the Type-2 Seesaw Mechanism.
Abstract: In the Standard Model there are several unsolved puzzles that motivate different extensions with new fields. For instance, the Type-2 Seesaw Mechanism is introduced to explain why neutrino masses are so tiny, however, this model cannot explain other issues of the SM, e.g. Dark Matter. Thus, this theory could also be regarded as incomplete, needing another (heavy) field to solve other open questions of the SM. This motivates the construction of an expansion of the Type-2 Seesaw model to allow for dimension 5 and 6 operators. In this, talk I will present the basis of operators of SM fields + Type-2 Seesaw up to dimension 6 and show different ways of constraining this parameter space, discussing phenomenological pros and cons that this kind of extension can offer us.
Date and time: Monday, October 25th, at 11:00 CEST
Speaker: Maria Ramos (UAM)
Title: Composite signals of new physics
Abstract: In this talk, I will discuss the phenomenology of several composite Higgs models where new pseudo-Nambu Goldstone bosons emerge at the electroweak scale, along with the Higgs boson, after the spontaneous breaking of a global symmetry. These exotic particles can explain several problems in particle physics, from dark matter to the flavour anomalies, leading to specific signatures at high energy facilities. After combining astrophysical and collider probes, I will show that large regions of the parameter space of the composite theories where the interesting phenomena can be addressed have not been probed by the experimental collaborations, therefore requiring significant efforts in order to be constrained.
Slides: files/Hidden_MariaRamos.pdf
Date and time: Monday, June 14th at 11:30 CEST
Speaker: Virgile Dandoy (KIT)
Title: Self-Consistent Dark Matter Halo from Axion Particles
Abstract: Instead of describing them through non-relativistic particles, axions have the very interesting property to be described by the non-relativistic approximation of the axion field itself. When coupled to their own gravitational field, their dynamic follows the Schrodinger-Poisson system. This wave dark matter (ψDM) once submitted to numerical simulations is able to probe some features of the dark matter halos and solve the disagreements between their observations and the cold dark matter (CDM) simulations. However, being more and more computationally challenging, ψDM halo simulations have their limitations. We illustrate here an analytical method to construct wave-halo solutions by making the link with collisionless particle distribution function. This analytic expression turns out to be very useful to probe the halo small scales and the other properties of the dark matter halos.
Slides: files/HIDDeN_Webinar-Dandoy.pdf
Date and time: Monday, May 10th at 11:00 CET
Speaker: Valentina Montoya (UHEI ESR)
Title: Cold Dark Matter Production. Non instantaneous reheating.
Abstract: We studied the perturbative decay of a massive scalar in the reheating era not necessarily identified as the inflaton. We explored how to produce dark matter relic density in both WIMP and FIMP scenarios and the coupling parameter space to obtain under a non standard cosmological model the right dark matter abundance. In particular for the FIMP case, we studied the relation between the dark matter mass and the reheating temperature to check the conditions under which the relic density can be kept unchanged during a subsequent radiation dominated era.
Finally we treated the massive scalar as a mixture between the inflaton and dark matter, and calculated its observables to restrict its vacuum expectation value (vev). We consider a reheating period produced through a dark portal for which we found a coupling between the visible and the dark sector of $\delta \approx 10^{-12}$ to achieve the right dark matter abundance.
Slides: files/SlidesValentina_MontoyaESR.pdf
Video: https://www.dropbox.com/s/v4mcgjdenfzxwxy/zoom_0.mp4?dl=0
Date and time: Monday, March 22nd at 11:00 CET
Speaker: Mario Fernández Navarro (SOTON ESR)
Title: Active-sterile neutrino oscillations in very low reheating scenarios
Abstract: Most neutrino oscillation experiments are well explained through the mixing of the three standard neutrino flavours of the SM, but some anomalies in short baseline oscillation experiments remain unexplained. These anomalies may be explained by the existence of an extra, sterile neutrino state, leading to the so-called 3+1 framework. However, this 3+1 scenario is highly constrained by cosmological observations, which favour the standard three-neutrino case. Here we present a way to accommodate the 3+1 scenario with the cosmological observations by suppressing the thermalisation of the sterile neutrino in the early Universe. We address this problem by considering an exotic cosmological scenario where we assume that a very late reheating process took place before BBN. In this scenario, the radiation epoch starts at temperatures of order MeV, in such a way that neutrinos may decouple from the cosmic plasma before they are fully thermalised.
Slides: files/HIDDeN_Webinar_MFN.pdf
Video: https://www.dropbox.com/s/9or4qh84g90joge/Webinar_ESR_Mario-Fdez-Navarro.mp4?dl=0
Date and time: Monday, February 15th at 12:00 CET
Speaker: Francesco Costa (UGOE ESR)
Title: Heavy field correction to the primordial power spectrum during inflation
Abstract: Nearly scale-invariant primordial power spectrum is one of the key features of cosmic inflation. To date, no sign of deviations from the simplest single-field inflation models has been observed. On the other hand, realistic models of inflation, meaning particle physics-based models, contain multiple fields other than the inflaton. The presence of heavy fields coupled to the inflaton may alter the predictions of the single-field inflation models.
In this project we consider the effects of heavy fields on the primordial power spectrum, studying a generic model that contains massive scalar and fermion fields coupled to the inflaton.
The radiative corrections introduce the presence in the power spectrum of time-dependent features of two types. One arises from the evolution of the background. The other is an oscillatory feature. The scalar and fermion contributions produce a constant shift and this peculiar oscillatory effects on top of the tree-level primordial power spectrum. Future improvements of CMB measurements may refine our current understanding of the primordial power spectrum and lead to a possible detection of these effects.
Slides: files/ESR-seminar-Heavy-field-correction-during-inflation.pdf
Video: https://www.dropbox.com/s/zb6vri20tv4myom/zoom_0.mp4?dl=0
