A
bstract
We consider a type-I seesaw framework endowed with a flavour symmetry, belonging to the series of non-abelian groups ∆(3
n
2
) and ∆(6
n
2
), and a CP symmetry. Breaking these symmetries in ...a non-trivial way results in the right-handed neutrinos being degenerate in mass up to possible (further symmetry-breaking) splittings
κ
and
λ
, while the neutrino Yukawa coupling matrix encodes the entire flavour structure in the neutrino sector. For a fixed combination of flavour and CP symmetry and residual groups, this matrix contains five real free parameters. Four of them are determined by the light neutrino mass spectrum and by accommodating experimental data on lepton mixing well, while the angle
θ
R
is related to right-handed neutrinos. We scrutinise for all four lepton mixing patterns, grouped into Case 1) through Case 3 b.1), the potential to generate the baryon asymmetry of the Universe through low-scale leptogenesis numerically and analytically. The main results are:
a
) the possible correlation of the baryon asymmetry and the Majorana phases, encoded in the Pontecorvo-Maki-Nakagawa-Sakata mixing matrix, in certain instances;
b
) the possibility to generate the correct amount of baryon asymmetry for vanishing splittings
κ
and
λ
among the right-handed neutrinos as well as for large
κ
, depending on the case and the specific choice of group theory parameters;
c
) the chance to produce sufficient baryon asymmetry for large active-sterile mixing angles, enabling direct experimental tests at current and future facilities, if
θ
R
is close to a special value, potentially protected by an enhanced residual symmetry. We elucidate these results with representative examples of flavour and CP symmetries, which all lead to a good agreement with the measured values of the lepton mixing angles and, possibly, the current indication of the CP phase
δ
. We identify the CP-violating combinations relevant for low-scale leptogenesis, and show that the parametric dependence of the baryon asymmetry found in the numerical study can be understood well with their help.
Abstract
We investigate non-perturbative production of fermionic dark matter in the early universe.
We study analytically the gravitational production mechanism accompanied by the coupling of
...fermions to the background inflaton field. The latter leads to the variation of effective fermion
mass during preheating and makes the resulting spectrum and abundance sensitive to its parameters.
Assuming fast preheating that completes in less than the inflationary Hubble time and no
oscillations of the inflaton field after inflation, we find an abundant production of particles
with energies ranging from the inflationary Hubble rate to the inverse duration of preheating.
The produced fermions can account for all observed dark matter in a broad range of parameters. As
an application of our analysis, we study non-perturbative production of fermionic dark matter in
the model of Palatini Higgs inflation.
We consider low-energy tests of low-scale leptogenesis based on the type I seesaw scenario with three right-handed singlet neutrinos νlR. In this scenario, successful leptogenesis is possible for ...quasi-degenerate in mass heavy Majorana neutrinos N1,2,3, M1,2,3≅M, |Mj−Mi|≪M, i≠j=1,2,3, heavy Majorana neutrino masses M∼(0.05−5×105) GeV, and Nj charged current and neutral current weak interaction couplings as large as O(10−2). We derive the constraints on the corresponding leptogenesis parameter space from the existing data from low-energy experiments, including the limits from the experiments on μ→eγ decay and on the rate of μ−e conversion in gold. We show also that the planned and upcoming experiments on charged lepton flavour violation with μ±, MEG II on the μ→eγ decay, Mu3e on μ→eee decay, Mu2e and COMET on μ−e conversion in aluminium and PRISM/PRIME on μ−e conversion in titanium, can probe significant region of the viable leptogenesis parameter space, and thus have a potential for a discovery. Experiments on τ→eee(μμμ) and τ→e(μ)γ decays (e.g., BELLE II) also can probe a part of the leptogenesis parameter space, although a relatively small one.
Abstract
We study preheating following Higgs inflation in the Palatini formulation of gravity. We
numerically evolve perturbations of the radial mode of the Higgs field and that of three scalars
...modeling the gauge bosons. We compare the two non-perturbative mechanisms of growth of
excitations — parametric resonance and tachyonic instability — and confirm that the latter plays
the dominant role. Our results provide further evidence that preheating in Palatini Higgs
inflation happens within a single oscillation of the Higgs field about the bottom of its
potential, consistent with the approximation of an instantaneous preheating.
The electron-positron stage of the Future Circular Collider, FCC-ee, is a frontier factory for Higgs, top, electroweak, and flavour physics. It is designed to operate in a 100 km circular tunnel ...built at CERN, and will serve as the first step towards ≥100 TeV proton-proton collisions. In addition to an essential and unique Higgs program, it offers powerful opportunities to discover direct or indirect evidence of physics beyond the Standard Model. Direct searches for long-lived particles at FCC-ee could be particularly fertile in the high-luminosity
Z
run, where 5 × 10
12
Z
bosons are anticipated to be produced for the configuration with two interaction points. The high statistics of Higgs bosons,
W
bosons and top quarks in very clean experimental conditions could offer additional opportunities at other collision energies. Three physics cases producing long-lived signatures at FCC-ee are highlighted and studied in this paper: heavy neutral leptons (HNLs), axion-like particles (ALPs), and exotic decays of the Higgs boson. These searches motivate out-of-the-box optimization of experimental conditions and analysis techniques, which could lead to improvements in other physics searches.
The sensitivity of direct searches for heavy neutral leptons (HNLs) in accelerator-based experiments depends strongly on the particles properties. Commonly used benchmark scenarios are important to ...ensure comparability and consistency between experimental searches, re-interpretations, and sensitivity studies for different facilities. In models where the HNLs are primarily produced and decay through the weak interaction, benchmarks are in particular defined by fixing the relative strengths of their mixing with SM neutrinos of different flavours, and the interpretation of experimental data is known to strongly depend on those ratios. The commonly used benchmarks in which a single HNL flavour exclusively interacts with one Standard Model generation do not reflect what is found in realistic neutrino mass models. We identify two additional benchmarks for accelerator-based direct HNL searches, which we primarily select based on the requirement to provide a better approximation for the phenomenology of realistic neutrino mass models in view of present and future neutrino oscillation data.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Particle physics today faces the challenge of explaining the mystery of dark matter, the origin of matter over anti-matter in the Universe, the origin of the neutrino masses, the apparent fine-tuning ...of the electro-weak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves new physics at mass scales comparable to familiar matter, below the GeV-scale, or even radically below, down to sub-eV scales, and with very feeble interaction strength. New theoretical ideas to address dark matter and other fundamental questions predict such feebly interacting particles (FIPs) at these scales, and indeed, existing data provide numerous hints for such possibility. A vibrant experimental program to discover such physics is under way, guided by a systematic theoretical approach firmly grounded on the underlying principles of the Standard Model. This document represents the report of the FIPs 2022 workshop, held at CERN between the 17 and 21 October 2022 and aims to give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
10.
Feebly-interacting particles Carenza, Pierluca; Milstead, David A.; Wallisch, Benjamin
The European physical journal. C, Particles and fields,
12/2023, Letnik:
83, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Particle physics today faces the challenge of explaining the mystery of dark matter, the origin of matter over anti-matter in the Universe, the origin of the neutrino masses, the apparent fine-tuning ...of the electro-weak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves new physics at mass scales comparable to familiar matter, below the GeV-scale, or even radically below, down to sub-eV scales, and with very feeble interaction strength. New theoretical ideas to address dark matter and other fundamental questions predict such feebly interacting particles (FIPs) at these scales, and indeed, existing data provide numerous hints for such possibility. A vibrant experimental program to discover such physics is under way, guided by a systematic theoretical approach firmly grounded on the underlying principles of the Standard Model. This document represents the report of the FIPs 2022 workshop, held at CERN between the 17 and 21 October 2022 and aims to give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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