41,681 research outputs found
Stable fermion mass matrices and the charged lepton contribution to neutrino mixing
No full textWe study the general properties of hierarchical fermion mass matrices in which the small eigenvalues are stable with respect to perturbations of the matrix entries and we consider specific applications to the charged lepton contribution to neutrino mixing. In particular, we show that the latter can account for the whole lepton mixing. In this case a value of sin θ13≳ me/mμsin θ23≈ 0.03, as observed, can be obtained without the need of any fine-tuning, and present data allow to determine the last row of the charged lepton mass matrix with good accuracy. We also consider the case in which the neutrino sector only provides a maximal 12 rotation and show that i) present data provide a 2σ evidence for a non-vanishing 31 entry of the charged lepton mass matrix and ii) a plausible texture for the latter can account at the same time for the atmospheric mixing angle, the θ13angle, and the deviation of the θ12angle from π/2 without fine-tuning or tension with data. Finally, we show that the so-called “inverted order” of the 12 and 23 rotations in the charged lepton sector can be obtained without fine-tuning, up to corrections of order me/mμ. © 2014, The Author(s)
Exploiting dijet resonance searches for flavor physics
No full textIn this work, we reinterpret ATLAS and CMS dijet resonance searches to set robust constraints on all hypothetical tree-level scalar and vector mediators with masses up to 5 TeV, assuming a diquark or a quark-antiquark coupling with an arbitrary flavor composition. To illustrate the application of these general results, we quantify the permissible size of new physics in consistent with the absence of signal in dijet resonance searches. Along the way, we perform a full SMEFT analysis of the aforementioned non-leptonic B meson decays at leading-order in α. Our findings uncover a pressing tension between the new physics explanations of recently reported anomalies in these decays and the dijet resonant searches. The high-p constraints are crucial to drain the parameter space consistent with the low-p flavor physics data.In this work, we reinterpret ATLAS and CMS dijet resonance searches to set robust constraints on all hypothetical tree-level scalar and vector mediators with masses up to 5 TeV, assuming a diquark or a quark-antiquark coupling with an arbitrary flavor composition. To illustrate the application of these general results, we quantify the permissible size of new physics in consistent with the absence of signal in dijet resonance searches. Along the way, we perform a full SMEFT analysis of the aforementioned non-leptonic meson decays at leading-order in . Our findings uncover a pressing tension between the new physics explanations of recently reported anomalies in these decays and the dijet resonant searches. The high- constraints are crucial to drain the parameter space consistent with the low- flavor physics data
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The David W. Fentress Family Letters, 1856-1969
No full textTranscript of a letter by an unidentified author to David Fentress regarding sharing federal newspapers and the banning of federal newspapers in some areas. The author passes on the news of the war including the destruction of the Federal merchantmen by the Confederate fleet. He passes along world news: Russia preparing to go to War with Europe and how that could negatively affect the Confederacy. There is also speculation on the future of the war
Addressing the B-physics anomalies in a fundamental Composite Higgs model
No full textAbstract I present a model addressing coherently the naturalness problem of the electroweak scale and the observed pattern of deviations from the Standard Model in semileptonic decays of B mesons. The Higgs and the two scalar leptoquarks responsible for the B-physics anomalies, S1=3¯,1,1/3 and S3=3¯,3,1/3 , arise as pseudo Nambu-Goldstone bosons of a new strongly coupled sector at the multi-TeV scale. I focus on an explicit realization of such a dynamics in terms of a new strongly coupled gauge interaction and extra vectorlike fermions charged under it. The model presents a very rich phenomenology, ranging from flavour observables, Higgs and electroweak precision measurements, and direct searches of new states at the LHC
The David W. Fentress Family Letters, 1856-1969
No full textTranscript of a letter by an unidentified author to David Fentress regarding sharing federal newspapers and the banning of federal newspapers in some areas. The author passes on the news of the war including the destruction of the Federal merchantmen by the Confederate fleet. He passes along world news: Russia preparing to go to War with Europe and how that could negatively affect the Confederacy. There is also speculation on the future of the war
High- dilepton tails and flavor physics
No full textWe investigate the impact of flavor-conserving, non-universal quark-lepton contact interactions on the dilepton invariant mass distribution in processes at the LHC. After recasting the recent ATLAS search performed at 13 TeV with 36.1 of data, we derive the best up-to-date limits on the full set of 36 chirality-conserving four-fermion operators contributing to the processes and estimate the sensitivity achievable at the HL-LHC. We discuss how these high- measurements can provide complementary information to the low- rare meson decays. In particular, we find that the recent hints on lepton-flavor universality violation in transitions are already in mild tension with the dimuon spectrum at high- if the flavor structure follows minimal flavor violation. Even if the mass scale of new physics is well beyond the kinematical reach for on-shell production, the signal in the high- dilepton tail might still be observed, a fact that has been often overlooked in the present literature. In scenarios where new physics couples predominantly to third generation quarks, instead, the HL-LHC phase is necessary in order to provide valuable information
Higgs and beyond in the LHC era
No full textThe last few years witnessed some major breakthroughs in the field of fundamental particle physics, which had a big impact in our understanding of Nature at a microscopic level.
On March 30th, 2010, the first proton-proton collisions took place at the Large Hadron Collider (LHC), marking the beginning of a new era in particle physics. The excellent performance of the machine and the detectors, due to the fantastic work of all the researchers involved in the experiments, lead, in only two years, to the announcement of the discovery of the Higgs boson on July 4th, 2012. This event could be considered as the peak of success for the Standard Model (SM) of elementary particles, which predicted the existence of this particle – as well as all its properties – since more than forty years before. In the following two years the ATLAS and CMS experiments at the LHC measured the properties of the Higgs particle with a good accuracy, showing no significant deviation from the SM. In the meanwhile, also the numerous direct searches for other new particles turned out to give only negative results, against all expectations from the theory community, pushing the scale of new physics to higher and higher values. Also, while the cosmological evidence for Dark Matter (DM) is now stronger than ever, so far all direct and indirect searches provided negative results (albeit with some isolated exceptions which, however, are still much debated in the literature and seem to be incompatible with other negative results) and the bounds on weakly interacting massive particle DM are extremely strong.
In neutrino physics an important event took place in June 2011, when the Tokay-to-Kamioka (T2K) collaboration reported an evidence for a non-zero, and sizable, value of the reactor neutrino mixing angle, θ13. This was confirmed in March 2012 by the Daya Bay collaboration, which measured this mixing angle with a very high precision, confirming that its value lies on the high-end of previous upper bounds. Since many popular and well motivated models of neutrino mixing predicted a zero, or very small, value of the reactor angle, this result was very important and offered a new insight in the quest for understanding the origin of flavor in the lepton sector. Also, since CP violation in the lepton sector effects vanish in the θ13 → 0 limit, the fact that this angle is sizable opens up many interesting possibilities for measuring CP violation in the neutrino sector.
The work presented in this thesis was largely stimulated by these two major breakthroughs in particle physics.
On the one hand the Higgs discovery and the measurement of its properties, in particular its mass, lead us to study the consequences of these measurements for a specific class of models beyond the SM: composite Higgs models (and also in supersymmetric versions of these models). In particular, we found that a very definite (and testable) prediction for the spectrum of new physics can be obtained: fermionic top partners are expected to be near the ∼1TeV scale. Also, the measurements of the Higgs couplings and the fact that the bounds for the new physics scale are often much higher than the electroweak scale, open up the possibility of studying possible deformations from the SM in an effective field theory framework. In this context we studied the possibility of linking the properties of the Higgs with other electroweak observables, very well constrained by LEP, via renormalization group effects, finding that they already allow to derive constraining, and independent, bounds on some Higgs properties. In the future, when some deviation from the SM will be – hopefully – observed, these effects could provide a new window on the new physics sector.
On the other hand, we studied how the measured value of θ13 can be accommodated in some motivated models of neutrino mixing by exploiting corrections due to the mixing among the charged leptons. Such corrections are expected, for example, in Grand Unified Theories, which allow to link the charged lepton sector with the quark sector, and therefore the neutrino mixing matrix with the quark mixing one. This analysis allowed us to obtain a precise prediction for the value of the Dirac CP violating phase in neutrino mixing, testable by future neutrino experiments
Minimal Explanation of Flavor Anomalies: B-Meson Decays, Muon Magnetic Moment, and the Cabibbo Angle
No full textSignificant deviations from the standard model are observed in semileptonic charged and neutral-current B decays, the muon magnetic moment, and the extraction of the Cabibbo angle. We propose that these deviations point towards a coherent pattern of new physics effects induced by two scalar mediators, a leptoquark S-1 and a charged singlet phi(+). While S-1 can provide solutions to charged-current B decays and the muon magnetic moment, and phi(+) can accommodate the Cabibbo-angle anomaly independently, their one-loop level synergy can also address neutral-current B decays. This framework provides the most minimal explanation to the above-mentioned anomalies, while being consistent with all other phenomenological constraints
Portrait of author David Foster at the National Library of Australia, Canberra, 8 June 2011 /
No full textTitle from acquisitions documentation.; Part of the collection: Portraits of author David Foster at the National Library of Australia, Canberra, 8 June 2011.; Acquired in digital format; access copy available online.; Mode of access: Online.; Photographed by a staff member of the National Library of Australia
Author David Foster with academic Jeff Doyle at the National Library of Australia, Canberra, 8 June 2011 /
No full textTitle from acquisitions documentation.; Part of the collection: Portraits of author David Foster at the National Library of Australia, Canberra, 8 June 2011.; Acquired in digital format; access copy available online.; Mode of access: Online.; Photographed by a staff member of the National Library of Australia
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