Cavity alignment using fringe scanning, Laura Paulina Šinkunaite
Speaker: Laura Paulina Šinkunaite
Abstract: LIGO employs two 4-km long FabryProt arm cavities, which need to be aligned in order for an interferometer to be locked on a TEM00 mode. Once the cavity is locked, alignment signals can be derived from wave-front sensors which measure the TEM01 mode content. However, the alignment state is not always good enough for locking on TEM00. Even when this is the case, the alignment can be evaluated using a free swinging cavity, that shows flashes when higher-order modes become resonant. By moving test masses, small changes are made to the mirror orientation, and hence the TEM00 mode can be optimized iteratively. Currently, this is a manual procedure, and thus
it is very time-consuming. Therefore, this project is aimed to study another possible way to lock the cavity on the TEM00 mode. Misalignment information can also be extracted from the power of the higher-order modes transmitted through the cavity. This talk will present an algorithm for this alternative and faster way to derive the alignment state of the arm cavities.
Video: http://reunion.uv.es/p997a1oqhvw/
Slides: http://reunion.uv.es/p1uzteqj5kr/
Axion Miniclusters, Julia Stadler
Speaker: Julia Stadler
Abstract: The QCD axion is among the best motivated candidates for Dark Matter. In a scenario, where the Peccei Quinn symmetry is restored after inflation the axion field acquires random initial values in causally disconnected patches of our universe. When the axion potential develops around the QCD phase transition fluctuations in the axion field are transferred into order 1 differences in the density contrast on comoving scales of roughly 0.02 pc. Besides, the decay of cosmic strings and domain walls, which are present as remnant of the phase transition, might add further inhomogeneities to the axion density. The regions of high overdensity collapse already around matter radiation equality, forming so called axion miniclusters.
The existence of axion miniclusters is crucial to the outcome of axion dark matter direct detection experiments but also of possible indirect signatures. In order to accurately predict the properties of miniclusters detailed knowledge of the density contrast previous to gravitational collapse is crucial.
In this talk I explain the production of axions from misalignment, string and wall decay and the difficulties in modeling these processes numerically. I continue by showing recent results of our numerical simulations, which follow the evolution of the axion field around the time of the QCD phase transition and determine the resulting density contrast, for the first time including all three relevant production processes. Our simulations indicate that the inclusion of strings and domain walls puts fluctuation power in scales, which are smaller than the horizon at the time of the QCD phase transition and we expect a large hierarchy of masses extending down to those smaller
scales.
Video: http://reunion.uv.es/p4zpslarfeq/
Slides: http://reunion.uv.es/p40mgmatw0i/
Cosmological evolution of axions in the presence of a baryon bath, Gonzalo Alonso
Speaker: Gonzalo Alonso
Abstract: Axion-like particles that couple to QCD via a G∧G term can induce a dependence of the mass of the proton and the neutron on the value of the axion field. It has been argued that an axion that couples too strongly to QCD results in the
underproduction of 4He during Big Bang Nucleosynthesis (BBN), which sets bounds on the allowed mass and decay constant of the axion. However, this very same effect results in a temperature-dependent effective potential for the axion in the presence of a background density of baryons, as there was in the early universe. Studying this effective potential leads to a deviation in the cosmological evolution of the axion field that can affect the BBN bounds.
Flavour-violating leptonic decays in the nuMSM, Fiona Kirk
Speaker: Fiona Kirk
Abstract: The neutrino Minimal Standard Model (nuMSM) allows to simultaneously explain neutrino oscillations, the existence of dark matter and the baryon asymmetry of the Universe, simply by completing the SM with three right-handed neutrinos with Majorana masses below the electroweak scale.
These BSM-particles can be searched for applying current day technology and experimental techniques, the only complication being the weak interaction rates. One way of testing the nuMSM is to study processes whose branching ratios are considerably enlarged by contributions of right-handed neutrinos. The nuMSM predictions for the branching ratios of flavour-violating muon decays were already estimated in [1], both flavour-violating muon and flavour violating tauon decays were considered here. All examined branching ratios were found to be too small to be detectable in near future, this being in agreement with the results of [1]. However, the application of the Casas- Ibarra parametrisation allowed for new insights into the role of the CP-violation phases in flavour-violating processes.
Little Conformal Symmetry and Neutral Naturalness, Rachel Houtz
Date and time: December 18 th, 2017 17:00 CET
related by an internal symmetry of the Lagrangian, but instead the symmetry relation that ensures the cancellation arises at an infrared
fixed point. Such a cancellation mechanism can, a la Little Higgs models, push the scale of the new physics that completely solves the
hierarchy problem up to 5-10 TeV. When embedded in a supersymmetric model, the superpartner masses provide the cutoffs for the loops, and
the mechanism alleviates the stop mass dependence on the Higgs mass parameter. We examine the case of a gauge boson top partner and a new
scalar top partner neutral under QCD.
The Quest for the Origin of Neutrino Masses, Josu Hernandez
Date and time: December 4th, 2017 at 11:00 CET
Speaker: Josu Hernandez
Title: The Quest for the Origin of Neutrino Masses
Abstract: Despite the remarkable agreement between a wide range of SM predictions and their experimental measurements, the SM has to be extended in order to explain the overwhelming experimental evidence from the neutrino oscillation phenomena supporting the existence of neutrino masses and mixings, which are absent in the SM. A simple and natural extension to account for neutrino masses is to introduce right-handed neutrinos in the particle content of the SM. Since these extra right-handed neutrinos are singlets under the SM gauge group, a Majorana mass term for these fermions is therefore allowed in the Lagrangian. One possibility is that this Majorana scale is above the EW scale but in the 100 GeV-TeV range. Then, the masses of the left-handed neutrinos arise in a simple way after ESB through the Weinberg operator in a low scale SM-Seesaw. In this situation, the presence of the new degrees of freedom will induce deviations from unitarity in the leptonic mixing matrix that appears in the charged current interactions. Thus, processes mediated by the weak currents would be modified, and therefore precision measurements of electroweak and flavor observables become a powerful tool to probe for the existence of heavy Majorana neutrinos. Following this idea, a global fit to the most complete and updated stringent set of electroweak and flavour observables to constrain the mixing of the extra heavy right-handed neutrinos in a model independent way has been performed. On the other hand, at some level, the addition of right-handed neutrinos will also impact neutrino oscillation searches. Therefore, the expected sensitivities of new generation of neutrino oscillation experiments to probe for this New Physics will be discussed too.
Slides: http://reunion.uv.es/p3h4lzf17h1/
Video: http://reunion.uv.es/p8oadu2iaop/
Leptonic CP Violation from Discrete Flavour Symmetries, Arsenii Titov
Date and time: November 20th, 2017 at 11 CET
Detecting a Double Disk of Dark Matter (DDDM) with binary pulsars, Andrea Caputo
Date and time: May 17th at 10 CET
Speaker: Andrea Caputo
Abstract: Pani (2015) updated upon a nice way to constrain the dark matter density using binary pulsars. The idea is that during the motion of a binary pulsar around the Galactic center, the pulsar and its companion experience a wind of dark-matter particles that would lead to a change in the orbital period, that might be detectable given the astonishing precision timing of pulsars. However, Pani (2015) only considered a smooth background dark matter density, which results in too weak constraints. We focus instead our analysis in the interesting and rich scenario of a dark disk (DD); in particular we look upon the model proposed by Fan et al (2013) for a Double-Disk Dark Matter(DDDM). In this case, the enhancement in the signal is manifest, and it is due to different causes: higher dark matter density, lower velocity dispersion for dark matter particles and binary's co-rotation with DD.
Dynamical Clockwork axions, Rupert Coy
Date and Time: April 26th at 10 CET
Speaker: Rupert Coy
Abstract: The clockwork mechanism is a novel method for generating a large separation of scales naturally through a pattern of symmetry breaking. I shall outline how the mechanism can arise from strongly-coupled theories at the TeV scale. This provides a nice way to connect (nearly) EW-scale physics with UV physics, such as axions, GUTs, and inflation. Using the composite axion as a specific example, I will describe some of the interesting phenomenology that emerges from this realisation of the clockwork mechanism.
eV Sterile Neutrino and reactor anomaly, Alvaro Hernandez Cabezudo
Date and time: April 6, 2017 @ 10:00 CET
Speaker: Alvaro Hernandez Cabezudo
Abstract: Neutrino oscillations in context of the 3 flavour neutrino scenario has been a very satisfactory explanation for lots of neutrino appearance and disappearance observations, being also the first evidence for physics beyond the standard model. But there are some experimental observations, that disagree with this framework. These observations, LSND, reactor and gallium anomalies could be explain with an additional neutrino mass eigenstate with a confidence around 3?.Concerning the reactor anomaly, the neutrino flux of the power plants is not very well understood, so it is very important to be aware of that when doing combined analysis of the different reactor neutrino experiments. A combined analysis is crucial, since these experiments work in different regimes of baselines, being complementary and covering different ranges of mass and mixing of the new neutrino. In the near future, a lot of reactor neutrino experiments will come and it will be possible to determine if these anomalies are due to this hypothetical neutrino.
Slides: http://reunion.uv.es/p1rg7h6nu3e/
Video: http://reunion.uv.es/p5m1qebfce8/
How high is the neutrino floor in dark matter direct detection experiments?, Elena Perdomo
Date and time: March 22, 2017 @ 11:00 CET
Speaker: Elena Perdomo (SOTON)
Abstract: We study standard and non-standard neutrino signals in direct dark matter detection experiments. The next generation of dark matter detectors will be soon sensitive to solar neutrinos via coherent neutrino-nucleus scattering. In this work, we compare the nuclear recoil rates expected from neutrino scattering with weakly interacting massive particle (WIMP) signals and we show that the scattering of neutrinos is an irreducible background for direct dark matter searches. We explore the possibility that neutrino interactions are enhanced by new physics with light mediators. We emphasize that the neutrino floor can be raised in the case that new scalar and vector mediators exist. Finally, we show how on the one hand, direct dark matter searches can be useful to probe or set constraints in new physics beyond the Standard Model, but on the other hand, their signatures could also be confused with dark matter signals.
Video :http://reunion.uv.es/p818x8j11ei/
Slides:http://reunion.uv.es/p3s476cwp70/
Studies of a magnesium fluoride photomultiplier tube for neutrinoless double beta decay experiments, Chloe Ransom
Speaker: Chloe Ransom
Abstract: Many extensions of the Standard Model explain the dominance of matter over antimatter in our Universe by neutrinos being their own anti-particles. This would imply that a lepton number violating radioactive decay named neutrinoless double beta (0???) decay exists, whose detection requires the upmost suppression of background. The Gerda collaboration searches for 0??? decay of Ge76 by operating bare germanium detectors, enriched in Ge76, in liquid argon. The Gerda experiment has instrumented the liquid argon (LAr) around the detecotr array with photomultiplier tubes (PMTs) for the readout of scintillation light thereby providing an active LAr veto system for background events. The PMTs currently used are not sensitive to LAr scintillation light, and use wavelength shifting foil to shift the LAr scintillation light to their region of sensitivity. A new PMT with a magnesium fluoride (MgF2) window is transparent to the LAr scintillation light, and therefore does not require the wavelength shifting foil. Reduction of material is important for a zero-background experiment such as Gerda. I present a summary of measurements made so far with this PMT, including gain, dark current and afterpulses rate, at both room temperature and cooled with nitrogen. Future work will include long-term tests in LAr.
Video: http://reunion.uv.es/p9rmuipoxvz/
Slides: http://reunion.uv.es/p1poei9to5r/
Minimal Lepton Flavour Violation Type III seesaw model at LHC, Nuno Agostinho
Speaker: Nuno Agostinho
Abstract: Nowadays, neutrinos are the most astonishing evidence of Physics Beyond the Standard Model. The well-known seesaw mechanism provides a simple and natural way to give small masses to the three Standard Model neutrinos. The smallness of neutrinos is generated at an energy many orders of magnitude above the TEV scale. An obvious question is whether the manifestation of particles that mediate neutrino interactions can be within the LHC reach.
One will focus on a very interesting possibility of generating neutrino masses through a simple seesaw type III model, with minimal flavour violation. Within this context, the mass of neutrinos can be generated by fermion triplets. The advantage of the seesaw type III is that via electroweak gauge interactions, the decays of the triplets can have cross-sections that could allow for their observation at the LHC.
Therefore, in principle, the triplets can be light enough to be produced at the LHC (in type-I seesaw, one adds heavy neutrino singlets that can be produced in association with charged leptons, however, the small mixing with the Standard Model particles leads to unsatisfactory production rates for the new fermions).
Furthermore, these types of models have characteristic signatures such as suppressed lepton violation decays of the triplet fermions and predictable lepton flavour composition of the states produced in their decays and, during the presentation, some examples will be given.
Slides: http://reunion.uv.es/p1tkru4jqsq/
Corrections to leptonic sum rules, Julia Gehrlein
Speaker: Julia Gehrlein
Abstract: Correlations between light neutrino observables are common predictions of a large class of models based on the (discrete) symmetry approach to lepton flavour. Neutrino mass sum rules connect the three (complex) light neutrino mass eigenvalues among each other and mixing sum rules relate the leptonic mixing angles and the Dirac phase. However, in nearly all cases known, the sum rules are not exact and receive corrections from various sources. We will discuss generic corrections to these sum rules which arise for example from higher dimensional operators or renormalisation group evolution and present the effect of the corrections on the predictions from sum rules found in the literature. While in most cases the predictions of mass sum rules are fairly stable running effects for the mixing sum rules have to be taken into account to realistically probe the predictions from the sum rules in concrete models.
Video: http://reunion.uv.es/p44ity9scqa/
Slides: http://reunion.uv.es/p89r6ojsgsj/
Electroweak Sector Under Scrutiny: A Combined Analysis of LHC > and Electroweak Precision Data
Date and time: December 17th at 11:00 AM CET
Speaker: Nuno Rosa Agostinho
Abstract: Presently, the negative results of the search for direct new physics effects indicate that new states are probably heavy, therefore, there might exist a mass gap between the SM states and the new ones. Thus, against this background, effective lagrangians raise as a most adequate tool for scientific advancement and we perform a comprehensive study of the Higgs couplings, gauge-boson couplings to fermions and triple gauge boson vertices. Our framework of effective theories includes the effects of the dimension-six operators contributing to these observables. We quantify the improvement on the determination of the 20 Wilson coefficients by the inclusion of the Run 2 results and we discuss the discrete (quasi)-degeneracies existing in the parameter space of operator coefficients relevant for the Higgs couplings to fermions and gauge bosons.
Natural and Dynamical Neutrino Mass Mechanism at the LHC
Date and time: November 26th at 11:00 AM CET
Speaker: Julia Gehrlein
Abstract: We generalize the scalar triplet neutrino mass model, the type II seesaw. Requiring fine-tuning and arbitrarily small parameters to be absent leads to dynamical lepton number breaking at the electroweak scale and a rich LHC phenomenology. A smoking gun signature at the LHC that allows to distinguish our model from the usual type II seesaw scenario is identified. Besides, we discuss other interesting phenomenological aspects of the model such as the presence of a massless Goldstone boson and deviations of standard model Higgs couplings.
Early seeds of Axion Miniclusters
Date and time: November 12th at 10:30 AM CET
Speaker: Julia Stadler
Abstract: Axions can be produced in the early universe at very low momenta by the misalignment mechanism and provide an excellent candidate for dark matter. However, the resulting axion population is expected to exhibit large inhomogeneities, if the Peccei Quinn symmetry is restored after inflation. Such fluctuation of $\mathcal(O)(1)$ collapse very early, around matter radiation equality, and form dense lumps of dark matter called axion miniclusters. The relevant mass scale for axion miniclusters is about $10^{-12} M_\astrosun$. Not only could the miniclusters dramatically modify direct detection constraints but also would they offer a new way of testing axion dark matter -- via their gravitational lensing signal. Cosmological defects, inevitablely present in cosmological scenarios which lead to minicluster formation, and a large separation of scales make the prediction of the density contrast challenging. The density contrast, however, determines the mass spectrum and fraction of dark matter defined in miniclusters.
Slides: http://reunion.uv.es/pzg3eiu5od/
Sneutrino Dark Matter in the BLSSM
Date and time: October 22nd at 11:00 AM CET
Speaker: Simon J. D. King
Abstract: In the framework of the (B - L) Supersymmetric Standard Model (BLSSM), we assess the ability of ground and space based experiments to establish the nature of its prevalent Dark Matter (DM) candidate, the sneutrino, which could either be CP-even or -odd. Firstly, by benchmarking this theory construct against the results obtained by the Planck spacecraft, we extract the portions of the BLSSM parameter space compliant with relic density data. Secondly, we show that, based on current sensitivities of the Fermi Large Area Telescope (FermiLAT) and their future projections, the study of high-energy ?-ray spectra will eventually enable us to extract evidence of this DM candidate through its annihilations into W+W? pairs (in turn emitting photons), in the form of both an integrated flux and a differential energy spectrum which cannot be reconciled with the assumption of DM being fermionic (like, e.g., a neutralino), although it should not be possible to distinguish between the scalar and pseudoscalar hypotheses. Thirdly, we show that, while underground direct detection experiments will have little scope in testing sneutrino DM, the Large Hadron Collider (LHC) may be able to do so in a variety of multi-lepton signatures, with and without accompanying jets (plus missing transverse energy), following data collection during Run 2 and 3.
Low Energy Unimodular Gravity
Date and time: October 8th at 11:00 AM CET
Speaker: Sergio González
Abstract: The theory of Unimodular Gravity(UG) has been proposed as apossible solution of the cosmological constant problem yielding the same classical predictions than General Relativity (GR). In this talk I will construct the quantum formulation of the theory and show that the cosmological constant is still protected. Furthermore, some quantum effects in the presence of matter are also analyzed and compared with the ones from GR, showing that, so far, there is no way to distinguish between both theories.
Color Unified Dynamical Axion
Date and time: May 4th, 2018 @ 17:00 CET
Speaker: Rachel Houtz (UAM)
Predictive Leptogenesis from Minimal Flavour Violation
Speaker: Salvador Rosauro
Computing inflationary predictions in general scalar-tensor theories, Hector Ramirez
Filling the gap in GUNS: the solar neutrino flux at keV energies, Eduardo Vitagliano
Date and time: Monday March 12th at 16:00 CET
Speaker: Edoardo Vitagliano
Title: Filling the gap in GUNS: the solar neutrino flux at keV energies
Abstract: In the last few decades we have entered a new era in neutrino observations, from cosmic neutrino background detection proposals to high energy neutrinos astronomy. As theorists, we have to provide the expected flux at different energies. In this talk, I will discuss about a previous overlooked contribution to the "grand unified neutrino spectrum" (GUNS) at Earth: the Solar neutrino thermal flux at keV energies. Besides being a signal, such a flux would also be the background for a futuristic keV sterile neutrino direct detection experiment. I will review the processes contributing to this spectrum, with particular emphasis on thermal effects due to the presence of a plasma.
Slides: http://reunion.uv.es/p494q34whgc/
Video: http://reunion.uv.es/p1siho7q4se/
B-physics and lepton flavor (universality) violation, Olcyr Sumersari
A Unified Halo-Independent Formalism for Direct Detection Experiments, Samuel Witte
Date and time: February 12th, 2018 at 16:00 CET
Speaker: Samuel Witte
Title: A Unified Halo-Independent Formalism for Direct Detection Experiments.
Abstract: In this talk I will present a new formalism that quite generically allows for the comparison of direct dark matter detection data in a halo-independent manner. This formalism, based on theorems from convex geometry, effectively eliminates all caveats that had limited the applicability of previously developed halo-independent methods; for example, halo-independent comparisons can now be made between putative measurements of the annual modulation and upper limits on the scattering rate in a statistically unambiguous way.
Slides: http://reunion.uv.es/p3eaiu5el4c/
Video: http://reunion.uv.es/p12a6jgkjc9/
Lepton flavor violation from TeV neutrinos, Xabier Marcano
Date and time: January 15t, 2018 16:30 CET
Speaker: Xabier Marcano
Abstract: Flavor physics is fundamental for testing the standard model of particle physics and could be the key for discovering new physics. Nowadays, this kind of processes, observed in neutrino oscillations, give us the clearest evidence of the fact that the Standard Model of fundamental interactions needs to be modified. Some of the most popular theories that try to asses this issue postulate the existence of new heavy right-handed neutrinos, with masses in the energy range that the LHC experiment is currently exploring. We study the connection between the possible existence of these neutrinos and lepton flavor physics. We consider the inverse seesaw model as a particular realization of a low scale seesaw model and analyze its lepton flavor violating phenomenology, in particular the Higgs and Z boson decays to two leptons of different flavor. Moreover, we also explore the possibility of directly producing these new heavy neutrinos at the LHC.
Slides: http://reunion.uv.es/p7748sdlkqv/
Video: http://reunion.uv.es/p57vanvbhs9/
Gauge-Invariant Models of Sizeable DM-Neutrino Interactions
Date and time: May 27th at 11:00 AM CET
Speaker: Arsenii Titov
Abstract: We explore the possibility that dark matter interactions with Standard Model particles are dominated by interactions with neutrinos.
We examine whether it is possible to construct such a scenario in a gauge-invariant manner. We first study the coupling of dark matter to the full lepton doublet and confirm that this generally leads to the dark matter phenomenology being dominated by interactions with charged leptons. We then explore two different implementations of the neutrino portal in which neutrinos mix with a Standard Model singlet fermion that interacts directly with dark matter through either a scalar or vector mediator. In these cases we find that the neutrino interactions can dominate the dark matter phenomenology. Present neutrino detectors can probe dark matter annihilations into neutrinos and already set the strongest constraints on these realisations. Future experiments such as Hyper-Kamiokande, MEMPHYS, DUNE, or DARWIN could allow to probe dark matter annihilation cross section to neutrinos down to the value required to obtain the correct thermal relic abundance.
Looking for Axion Dark Matter: from Dwarf Galaxies to Pulsars
Date and time: May 6th, at 10:30 AM
Speaker: Andrea Caputo
Abstract: Axion and Axion-like particles are fascinating dark matter candidates and a great effort has been devoted to their study, both theoretically and experimentally. In this talk I will discuss two different astrophysical searches. The first one consists in looking with radio telescopes for the spontaneous decay of axion dark matter using different targets as Dwarf Galaxies, Clusters or the Galactic Center. The second one uses the parity violating axion interactions to exploit the extreme precision of pulsar timing measurements and look for oscillations in the polarization angle of the pulsar signal.
Energy calibration for the GERDA experiment
Date and time: April 9th at 11:30 AM
Speaker: Chloe Ransom
Abstract: The observation of the hypothetical process of neutrinoless double beta decay (0nbb) would demonstrate both lepton-number violation and the Majorana nature of the neutrino. The GERDA experiment searches for 0nbb of Ge-76 at LNGS, operating 36 kg of enriched germanium diodes that act simultaneously as both source and detector. Neutrinoless double-beta decay would be detected in calorimeters such as GERDA as a sharp peak at the Q-value (2039 keV for 76Ge). Determining the energy of events via dedicated calibrations of the detectors is therefore of key concern, in addition to precisely determining the energy resolution. Here I will discuss the calibration procedure of GERDA, the analysis of the calibration data, the determination of systematic uncertainties, and how these quantities affect the neutrinolessdouble-beta analysis and limit.
Sterile Neutrinos in Reactor and Accelerator Experiments
Date and time: March 25th, 2019
Speaker: Álvaro Hernández Cabezudo
Abstract: In this seminar I will remind you the status of the short baseline anomalies and their interpretation in terms of sterile neutrino oscillations, focusing on the strong tension between the appearance and the disappearance data sets, which tell us that the MiniBooNE and LSND excesses can not be interpreted in terms of active-sterile neutrino oscillations. I will bridge this issue to alternative explanations for the MiniBooNE excess, which since last summer is much more significant than LSND excess. The MiniBooNE low energy excess can not be explain by simple scenarios and any new explanation will have to deal with many constraints. I will summarize which are the most important constraints and requirements that have to be satisfied for the new models to explain the excess, giving as example some of the most recent proposals.
True axions and their true couplings
Date and time: March 4, 2019
Speaker: Gonzalo Alonso
Abstract: We review the status of CP-odd pseudoscalar searches at colliders and other high-energy physics experiments, highlighting the similarities and differences between axions, axion-like particles(ALPs) and other more exotic species of the "axion family? Aiming to determine the phenomenologically relevant interactions, we take into account loop effects and distinguish the model-dependent and -independent components of the couplings, with special focus on electroweak gauge bosons. The particular case of heavy axions is analysed in more detail, showing the potential of the LHC to probe ample new regions of parameter space. To this aim, a two-coupling-at-a-time approach is followed, showcasing the importance of not limiting the study to specific individual interactions.
SU(5) Grand Unified Theory with A_4 Modular Symmetry
Date and time: February 11, 2019
Speaker: Elena Perdomo
Abstract: I will give an introduction to modular symmetries and how these symmetries can be interpreted as a family symmetry. Afterwards, I will focus on an SU(5) model in 6d where the two extra dimensions are compactified on a T_2/Z_2 orbifold, with a twist angle of \omega= ei2pi/3. Such construction suggests an underlying modular A_4 symmetry, leading to an effective \mu-\tau reflection symmetry at low energies.
This implies maximal atmospheric mixing and maximal leptonic CP violation.
An effective approach to lepton anomalies: the seesaw case
Date and time: January 21st 2019
Speaker: Rupert Coy
Abstract: In the absence of direct evidence of new physics, any UV theory can be reduced to its specific set of low-energy effective operators. As a case study, I derive the EFT for the seesaw extension of the Standard Model, with sterile neutrinos of mass M > m_W. All Wilson coefficients generated at 1-loop are systematically computed. Hence, it becomes straightforward to (i) identify the seesaw parameters compatible with the smallness of neutrino masses; (ii) compute precision lepton observables, which may be sensitive to scales as large as M ? 10^3 TeV; and (iii) establish sharp correlations among those observables. I find that the flavour-conserving Wilson coefficients set an upper bound on the flavour-violating ones. The low-energy limits on \mu -> e and \tau -> e,\mu transitions suppress flavour violation in Z and Higgs decays, as well as EDMs, far beyond the experimental reach.The precision measurements of G_F, m_W, and the invisible Z width set more stringent bounds than present and future limits on \tau -> e,\mu transitions. I will also present a spurion analysis to compare the seesaw with different models, thus assessing the discriminating potential of the effective approach.
