Despite the remarkable success of the Standard Model, the hierarchy and patterns of fermion masses and mixings remain a profound mystery. To address this, we propose a model employing the rank mechanism, where the originally massless quarks and leptons sequentially get masses. The third generation masses originate from the seesaw mechanism at the tree-level, while those of the second and first generations emerge from one-loop and two-loop radiative corrections, respectively, with a progressive increase in the rank of the mass matrix. This approach does not require new discrete or global symmetries. Unlike other theories of this type that require the introduction of additional scalars, we employ the double seesaw mechanism within a left-right symmetric framework, which allows us to realize this scenario solely through gauge interactions.

Germany

Sudip Jana

Sophie Klett

Manfred Lindner

United States

Rabindra Mohapatra

Radiative origin of fermion mass hierarchy in left-right symmetric theory

<p>The bounds on parameters of the eV and higher scale Majorana sterile neutrinos from the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> decay have been refined and updated. We present a simple and compact analytic expression for the bound in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">Δ</mi><msubsup><mrow><mi>m</mi></mrow><mrow><mn>41</mn></mrow><mrow><mn>2</mn></mrow></msubsup><mo>−</mo><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><mn>2</mn><msub><mrow><mi>θ</mi></mrow><mrow><mn>14</mn></mrow></msub></mrow></math> plane, which includes all relevant parameters. Dependencies of the bound on unknown <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> phases and the type of mass spectrum of light neutrinos (mass ordering and level of degeneracy) are studied in detail. We have computed the bounds using the latest and most stringent data from KamLAND-Zen. The projected constraints from future experiments are estimated. The obtained bounds are confronted with positive indications of the presence of sterile neutrinos as well as with the other existing bounds. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> decay results exclude the regions of parameters implied by BEST and Neutrino-4, and the regions indicated by LSND and MiniBooNE are in conflict with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> decay results combined with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>ν</mi></mrow><mrow><mi>μ</mi></mrow></msub></mrow></math>-disappearance bounds.</p>

Lucas Puetter

Alexei Yu. Smirnov

Restricting sterile neutrinos by neutrinoless double beta decay

The discovery of neutrino oscillations implies that neutrinos are massive and mixed, necessitating an extension of the Standard Model, which may require the introduction of nonstandard neutrino interactions (NSIs). We investigate the potential of a high-energy muon collider to probe such NSIs with muons, specifically focusing on muonic forces. By analyzing the monophoton signal from the process <math><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup><mo>→</mo><mi>ν</mi><mover><mi>ν</mi><mo>¯</mo></mover><mi>γ</mi></math>, we explore four-fermion contact interactions involving two muons and two neutrinos. Moreover, we examine minimal models that generate scalar and vector-mediated NSIs and study their phenomenology. Projected sensitivities for the strength of NSIs, <math><msubsup><mi>ε</mi><mrow><mi>α</mi><mi>β</mi></mrow><mrow><mi>μ</mi><mi>μ</mi></mrow></msubsup></math>, are presented at a 95% confidence level for a center-of-mass energy of 3 TeV and integrated luminosities of <math><mi>L</mi><mo>=</mo><mn>1</mn></math> and <math><mn>10</mn><mtext> </mtext><mtext> </mtext><msup><mi>ab</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>, showcasing the complementarity between a muon collider and other experimental probes.

Muonic force and nonstandard neutrino interactions at muon colliders

We present a proof-of-concept extension to the Standard Model that can generate a non-vanishing neutrinoless double beta decay (<math><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math>) signal without the existence of Majorana neutrinos or lepton number violation in the zero-density vacuum-ground-state Lagrangian. We propose that the <math><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> can be induced by the capture of an ultralight scalar field, a potential dark matter candidate, that carries two units of lepton number. This makes the observable <math><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> spectrum indistinguishable from the usual <math><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> mechanisms by any practical means. We find that a non-zero <math><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> rate does not require neutrinos to be fundamentally Majorana particles. However, for sizeable decay rates within the range of next-generation experiments, the neutrino will, generally, acquire an (effective) Majorana mass as the scalar field undergoes a transition to the Bose-Einstein condensate phase. We also discuss the distinction between the aforementioned scenario and the case in which the emission of a lepton-number-two scalar leads to <math><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math>, exhibiting discernible qualitative features that make it experimentally distinguishable from the conventional scenario.

Lukáš Gráf

Oliver Scholer

Nele Volmer

Neutrinoless double beta decay without vacuum Majorana neutrino mass

We show that the doubly charged scalar from the <math><mi>S</mi><mi>U</mi><msub><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow><mrow><mi>R</mi></mrow></msub></math>-triplet Higgs field in the Left-Right Symmetric Model has its mass governed by a hidden symmetry so that its value can be much lower than the <math><mi>S</mi><mi>U</mi><msub><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow><mrow><mi>R</mi></mrow></msub></math> breaking scale. This makes it a long-lived particle while being consistent with all existing theoretical and experimental constraints. Such long-lived doubly charged scalars have the potential to trigger catalyzed fusion processes in light nuclei, which may have important applications for energy production. We show that it could also bear consequences on the excess of large ionization energy loss (<math><mi>d</mi><mi>E</mi><mo>/</mo><mi>d</mi><mi>x</mi></math>) recently observed in collider experiments.

Evgeny Akhmedov

P.S. Bhupal Dev

Rabindra N. Mohapatra

Long-lived doubly charged scalars in the left-right symmetric model: Catalyzed nuclear fusion and collider implications

We investigate the effect of resonant spin conversion of the neutrinos induced by the geometrical phase in a twisting magnetic field. We find that the geometrical phase originating from the rotation of the transverse magnetic field along the neutrino trajectory can trigger a resonant spin conversion of Dirac neutrinos inside the supernova, even if there were no such transitions in the fixed-direction field case. We have shown that, even though resonant spin conversion is too weak to affect solar neutrinos, it could have a remarkable consequence on supernova neutronization bursts where very intense magnetic fields are quite likely. We demonstrate how the flavor composition at Earth can be used as a probe to establish the presence of non-negligible magnetic moments, potentially down to <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>15</mn></mrow></msup><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub></mrow></math> in upcoming neutrino experiments like the Deep Underground Neutrino Experiment and the Hyper-Kamiokande. Possible implications are analyzed.

Brazil

Yago Porto

Resonances of Supernova Neutrinos in Twisting Magnetic Fields

CERN

Carlotta Accettura

United Kingdom

Dean Adams

Rohit Agarwal

Claudia Ahdida

Italy

Chiara Aimè

Nicola Amapane

David Amorim

Paolo Andreetto

Fabio Anulli

Robert Appleby

Artur Apresyan

Aram Apyan

France

Sergey Arsenyev

Pouya Asadi

Egypt

Mohammed Mahmoud

Aleksandr Azatov

John Back

Lorenzo Balconi

Laura Bandiera

Roger Barlow

Nazar Bartosik

Emanuela Barzi

Fabian Batsch

Matteo Bauce

J. Berg

Andrea Bersani

Alessandro Bertarelli

Alessandro Bertolin

Kevin Black

Fulvio Boattini

Alex Bogacz

Maurizio Bonesini

Bernardo Bordini

Salvatore Bottaro

Luca Bottura

Alessandro Braghieri

Marco Breschi

Natalie Bruhwiler

Xavier Buffat

Laura Buonincontri

Philip Burrows

Graeme Burt

Dario Buttazzo

Barbara Caiffi

Marco Calviani

Simone Calzaferri

Daniele Calzolari

Rodolfo Capdevilla

Christian Carli

Fausto Casaburo

Massimo Casarsa

Luca Castelli

Maria Catanesi

Lorenzo Cavallucci

Gianluca Cavoto

Spain

Francesco Celiberto

Luigi Celona

Alessandro Cerri

Gianmario Cesarini

Cari Cesarotti

Portugal

Grigorios Chachamis

Antoine Chance

Switzerland

Siyu Chen

Yang-Ting Chien

Mauro Chiesa

Anna Colaleo

Francesco Collamati

Gianmaria Collazuol

Marco Costa

Nathaniel Craig

Camilla Curatolo

Canada

David Curtin

Giacomo Molin

Magnus Dam

Heiko Damerau

Sridhara Dasu

Jorge Blas

Stefania Curtis

Ernesto Matteis

Stefania Rosa

Jean-Pierre Delahaye

Dmitri Denisov

Türkiye

Haluk Denizli

Christopher Densham

Radovan Dermisek

Luca Luzio

Elisa Meco

Biagio Micco

Keith Dienes

Eleonora Diociaiuti

Tommaso Dorigo

Alexey Dudarev

Robert Edgecock

Filippo Errico

Marco Fabbrichesi

Stefania Farinon

Anna Ferrari

Jose Somoza

Netherlands

Frank Filthaut

Davide Fiorina

Erratum: Towards a muon collider

We present a minimal sub-GeV thermal Dark Matter (DM) model where the DM primarily interacts with neutrinos and participates in neutrino mass generation through quantum loop corrections at one-loop level. We discuss the challenges in achieving this in the scotogenic framework and identify a viable variant. Due to minimality and the interplay between obtaining the correct DM relic abundance and neutrino oscillation data, the model predicts (i) a massless lightest neutrino, (ii) enhanced rate of <math><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> decay due to loop corrections involving light DM exchange, and (iii) testable lepton flavor-violating signal <math><mi>μ</mi><mo>→</mo><mi>e</mi><mi>γ</mi></math>. Detecting monoenergetic neutrinos from DM annihilation in next-generation neutrino detectors offers a promising way to test this scenario.

Johannes Herms

Vishnu P.K.

Shaikh Saad

Light neutrinophilic dark matter from a scotogenic model

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.

Towards a muon collider

The question of how heavy a sterile neutrino can be probed in experiments leads us to investigate the Primakoff production of heavy sterile neutrinos from ultrahigh-energy neutrinos via the magnetic dipole portal. Despite the suppression from the small magnetic moment, the transition is significantly enhanced by tiny t-channel momentum transfers, similar to the resonant production of pions and axions in an external electromagnetic field. Based on the current IceCube measurement of astrophysical neutrinos up to PeV energies, strong constraints can already be derived on the transition magnetic moments of sterile neutrinos up to TeV masses. Moreover, we investigate the sensitivity of future tau neutrino telescopes, which are designed for EeV cosmogenic neutrino detection. We find that sterile neutrino masses as large as <math><mn>30</mn><mspace width="0.25em"></mspace><mtext>TeV</mtext></math> can be probed at tau neutrino telescopes such as GRAND, POEMMA, and Trinity.

Guo-yuan Huang

Werner Rodejohann

Probing heavy sterile neutrinos at neutrino telescopes via the dipole portal