arXiv subjects

Sokratis Trifinopoulos

Publications and source records attributed to Sokratis Trifinopoulos.

At least 37 records · Page 2Linked to original sources

arXiv2025

Searching for exotic scalars at fusion reactors

The energy created in deuterium-tritium fusion reactors originates from a high-intensity neutron flux interacting with the reactor's inner walls. The neutron flux can also be used to produce a self-sustaining reaction by lining the walls with lithium-rich `breeding blankets', in which a fraction of neutrons interacts with lithium, creating the tritium fuel. The high-intensity neutron flux can also result in the production of dark sector particles, feebly interacting light scalars or pseudoscalars, via nuclear transitions within the breeding blanket. We estimate the potential size of such dark sector flux outside the reactor, taking into account all current constraints, and consider possible detection methods at current and future thermonuclear fusion reactors. As a by-product, we also recast the SNO axion bound for a CP even scalar. We find that year-long searches at current and future reactors can set leading constraints on dark scalar -- and dark pseudoscalar -- nucleon couplings.

hep-ph↗

arXiv2024

New Physics at the Muon (Synchrotron) Ion Collider: MuSIC for several scales

A Muon (Synchrotron) Ion Collider (MuSIC) can be the successor to the Electron-Ion Collider at Brookhaven National Laboratory, as well as the ideal demonstrator facility for a future multi-TeV Muon Collider. Besides its rich nuclear physics and Standard Model particle physics programs, in this work we show that the MuSIC with a TeV-scale muon beam offers also a unique opportunity to probe New Physics. In particular, the relevant searches have the potential to surpass current experimental limits and explore new regimes of the parameter space for a variety of Beyond the Standard Model scenarios including: lepton-flavor violating leptoquarks, muonphilic vector boson interactions, axion-like particles coupling to photons, and heavy sterile neutrinos. Depending on the particular case, the sensitivity of the searches in the MuSIC may span a wide range of energy scales, namely from sub-GeV particles to the few TeV New Physics mediators. Our analysis demonstrates that the MuSIC can strike a powerful chord in the search for New Physics, thanks to unique combination of features that amplify its capabilities.

hep-ph↗

arXiv2024

Spontaneous symmetry breaking, gauge hierarchy and electroweak vacuum metastability

The so-called metastability bound asserts that an unnaturally small Higgs mass is a necessary condition for electroweak vacuum metastability, offering a new approach towards solving the hierarchy problem. So far, this result relies on the assumption of a negative Higgs mass parameter, or equivalently, on electroweak spontaneous symmetry breaking. We derive a new, corresponding bound for the case of a positive mass parameter. When the new bound is significantly more restrictive than or comparable to its established counterpart, it may offer an explanation for the sign of the Higgs mass parameter, and thus, spontaneous symmetry breaking itself. New physics at scales $\mathcal{O} (1-10)$ TeV can lower these bounds as far as the TeV-scale. As an illustration, we consider vacuum stability in the presence of additional TeV-scale fermions with Yukawa couplings to the Higgs, as well as a dimension-six term parameterizing new physics in the UV. This scenario requires new physics that couples strongly to the Higgs, and can potentially be probed at future colliders. Finally, to allow for comparison with concrete mechanisms predicting metastability, we provide the mass-dependent lifetime of the electroweak vacuum for this model.

hep-ph↗

arXiv2024

From Neurons to Neutrons: A Case Study in Interpretability

Mechanistic Interpretability (MI) promises a path toward fully understanding how neural networks make their predictions. Prior work demonstrates that even when trained to perform simple arithmetic, models can implement a variety of algorithms (sometimes concurrently) depending on initialization and hyperparameters. Does this mean neuron-level interpretability techniques have limited applicability? We argue that high-dimensional neural networks can learn low-dimensional representations of their training data that are useful beyond simply making good predictions. Such representations can be understood through the mechanistic interpretability lens and provide insights that are surprisingly faithful to human-derived domain knowledge. This indicates that such approaches to interpretability can be useful for deriving a new understanding of a problem from models trained to solve it. As a case study, we extract nuclear physics concepts by studying models trained to reproduce nuclear data.

cs.LG↗

arXiv2024

Scrutinizing the Primordial Black Holes Interpretation of PTA Gravitational Waves and JWST Early Galaxies

Recent observations have granted to us two unique insights into the early universe: the presence of a low-frequency stochastic gravitational wave background detected by the NANOGrav and Pulsar Timing Array (PTA) experiments and the emergence of unusually massive galaxy candidates at high redshifts reported by the James Webb Space Telescope (JWST). In this letter, we consider the possibility that both observations have a common origin, namely primordial black holes (PBHs) in the mass range between $10^{6}~M_{\odot}$ and $10^{13}~M_{\odot}$. While superheavy PBHs act as seeds for accelerated galaxy formation capable of explaining the JWST extreme galaxies, they can also form binary mergers that source gravitational waves which can be potentially identified as the PTA signal. The analysis is performed taking into account the constraints on the relevant region of the PBH parameter space including the novel bound imposed by the Ultraviolet Luminosity Function of galaxies observed by the Hubble Space Telescope. We conclude that PTA's and JWST's interpretations in terms of PBH binary mergers and Poissonian gas of PBHs, respectively, are strongly excluded.

astro-ph.CO↗

arXiv2023

LePDF: Standard Model PDFs for High-Energy Lepton Colliders

The emission of collinear radiation off an elementary lepton can be factorised from the hard scattering process by introducing Parton Distribution Functions of a Lepton (LePDF), which, contrary to protons, can be derived from first principles. In case of multi-TeV lepton colliders, such as the muon colliders currently being proposed, the complete structure of Standard Model interactions must be taken into account. In this work we solve numerically the corresponding DGLAP equations at the double-log order and provide public files with LePDFs for both muons and electrons, including polarisation effects. We discuss several interesting aspects of the resulting PDFs and compare them with the Effective Vector Approximation, showing that the latter fails to describe well the vector bosons PDFs at small momentum fractions, unless it is extended to higher orders.

hep-ph↗

arXiv2023

NuCLR: Nuclear Co-Learned Representations

We introduce Nuclear Co-Learned Representations (NuCLR), a deep learning model that predicts various nuclear observables, including binding and decay energies, and nuclear charge radii. The model is trained using a multi-task approach with shared representations and obtains state-of-the-art performance, achieving levels of precision that are crucial for understanding fundamental phenomena in nuclear (astro)physics. We also report an intriguing finding that the learned representation of NuCLR exhibits the prominent emergence of crucial aspects of the nuclear shell model, namely the shell structure, including the well-known magic numbers, and the Pauli Exclusion Principle. This suggests that the model is capable of capturing the underlying physical principles and that our approach has the potential to offer valuable insights into nuclear theory.

nucl-th↗

arXiv2023

Attracting the Electroweak Scale to a Tachyonic Trap

We propose a new mechanism to dynamically select the electroweak scale during inflation. An axion-like field $ϕ$ that couples quadratically to the Higgs with a large initial velocity towards a critical point $ϕ_c$ where the Higgs becomes massless. When $ϕ$ crosses this point, it enters a region where the Higgs mass is tachyonic and this results into an explosive production of Higgs particles. Consequently, a back-reaction potential is generated and the field $ϕ$ is attracted back to $ϕ_c$. After a series of oscillations around this point it is eventually trapped in its vicinity due to the periodic term of the potential. The model avoids transplanckian field excursions, requires very few e-folds of inflation and it is compatible with inflation scales up to $10^5~\rm GeV$. The mass of $ϕ$ lies in the range of hundreds of GeV to a few TeV and it can be potentially probed in future colliders.

hep-ph↗

arXiv2023

The remarkable role of the vector-like quark doublet in the Cabibbo angle and $W$-mass anomalies

The combination of precise determinations of $V_{us}$ and $V_{ud}$ hints towards a violation of the CKM first row unitarity at about $3σ$ level. Conversely, the recent measurement of the $W$-boson mass by the CDF Collaboration exhibits significant tension with the SM prediction, intensifying the conflict that may arise in models addressing the unitarity violation. We demonstrate that one vector-like $SU(2)_L$ doublet with mass of a few TeV mixing with light quarks and the top quark can simultaneously account for the two anomalies, without conflicting with flavour-changing phenomena and electroweak observables. Moreover, another tension in the value of the Cabibbo angle is reported also at $3σ$ level, between two determinations of $V_{us}$ obtained from semi-leptonic $K\ell3$ and leptonic $Kμ2$ kaon decays. We show that the vector-like doublet can be at the origin of this discrepancy and the substantial positive shift in the $W$-boson mass. This unique feature of the vector-like quark doublet may render it a crucial puzzle piece in new physics scenarios addressing the CKM unitarity problem. The model can be potentially probed in future colliders.

hep-ph↗

arXiv2022

New Physics in $b \to s μμ$: FCC-hh or a Muon Collider?

Rare flavour-changing neutral-current transitions $b \to s μ^+ μ^-$ probe higher energy scales than what is directly accessible at the LHC. Therefore, the presence of new physics in such transitions, as suggested by the present-day LHCb anomalies, would have a major impact on the motivation and planning of future high-energy colliders. The two most prominent options currently debated are a proton-proton collider at 100 TeV (FCC-hh) and a multi-TeV muon collider (MuC). In this work, we compare the discovery prospects at these colliders on benchmark new physics models indirectly detectable in $b \to s μ^+ μ^-$ decays but beyond the reach of the high-$p_T$ searches at the HL-LHC. We consider a comprehensive set of scenarios: semileptonic contact interactions, $Z^\prime$ from a gauged $U(1)_{B_3 - L_μ}$ and $U(1)_{L_μ- L_τ}$, the scalar leptoquark $S_3$, and the vector leptoquark $U_1$. We find that a 3 TeV MuC has a sensitivity reach comparable to the one of the FCC-hh. However, for a heavy enough mediator, the new physics effects at a 3 TeV MuC are only observed indirectly via deviations in the highest energy bin, while the FCC-hh has a greater potential for the discovery of a resonance. Finally, to completely cover the parameter space suggested by the $bsμμ$ anomalies, among the proposed future colliders, only a MuC of 10 TeV (or higher) can meet the challenge.

hep-ph↗

arXiv2022

Radiative Effects in the Scalar Sector of Vector Leptoquark Models

Gauge models with massive vector leptoquarks at the TeV scale provide a successful framework for addressing the B-physics anomalies. Among them, the 4321 model has been considered as the low-energy limit of some complete theories of flavor. In this work, we study the renormalization group evolution of this model, laying particular emphasis on the scalar sector. We find that, despite the asymptotic freedom of the gauge couplings, Landau poles can arise at relatively low scale due to the fast running of quartic couplings. Moreover, we discuss the possibility of radiative electroweak symmetry breaking, and characterize the fine-tuning associated with the hierarchy between the electroweak scale and the additional TeV-scale scalars. Finally, the idea of scalar fields unification is explored, motivated by ultraviolet embeddings of the 4321 model.

hep-ph↗

arXiv2022

Displaced Searches for Light Vector Bosons at Belle II

With a design luminosity of 50 ab$^{-1}$ and detectors with tracking capabilities extending beyond 1 m, the Belle II experiment is the perfect laboratory for the search of particles that couple weakly to the Standard Model and have a characteristic decay length of a few centimetres and more. We show that for models of dark photons and other light vector bosons, Belle II will be successful in probing regions of parameter space which are as of now unexplored by any experiment. In addition, for models where the vector boson couples sub-dominantly to the electron and quarks as compared to muons, e.g. in the $L_μ-L_τ$ model, Belle II will probe regions of mass and couplings compatible with the anomalous magnetic moment of muon. We discuss these results and derive the projected sensitivity of Belle II for a handful of other models. Finally, even with the currently accumulated data, $\sim 200$ fb$^{-1}$, Belle II should be able to cover regions of parameter space pertaining to the X(17) boson postulated to solve the ATOMKI anomaly.

hep-ph↗

arXiv2022

Explaining Flavour Anomalies with Heavy Scalars

Discrepancies between recent experimental results and their respective Standard Model predictions, known as flavour anomalies, are reported in semileptonic charged and neutral-current $B$-decays, the muon magnetic moment $(g-2)_μ$, and the extraction of the Cabibbo angle. In this proceedings, we review two New Physics models that introduce two scalar mediators at the TeV scale and aim at a combined explanation of the flavour anomalies. The first model features the leptoquarks $S_1$ and $S_3$ and provides tree level solutions to both $B$-anomalies and one-loop level solution to the anomalous $(g-2)_μ$. The second features the leptoquark $S_1$ and the charged singlet $ϕ^+$. While $S_1$ provides the same solution to the charged-current $B$-anomaly and $(g-2)_μ$ as in the first model, $ϕ^+$ can accommodate the Cabibbo-angle anomaly independently and together with $S_1$ can resolve the neutral-current $B$-anomaly at one-loop.

hep-ph↗

arXiv2021

From B-meson anomalies to Kaon physics with scalar leptoquarks

In this work we study possible connections between $B$-meson anomalies and Kaon physics observables in the context of combined solutions with the singlet and triplet scalar leptoquarks $S_1$ and $S_3$. By assuming a flavor structure for the leptoquark couplings dictated by a minimally broken $U(2)^5$ flavor symmetry we can make a sharp connection between these two classes of observables. We find that the bound on $\mathcal{B}(K^+ \rightarrow π^+ νν)$ from NA62 puts already some tension in the model, while the present limits on $\mathcal{B}(K_L \rightarrow μ^+ μ^-)$ and $μ\to e$ conversion in nuclei can be saturated. Relaxing instead the flavor assumption we study what values for $\mathcal{B}(K^+ \rightarrowπ^+ νν)$, as well as for $\mathcal{B}(K_L \rightarrowπ^0 νν)$ and $\mathcal{B}(K_{L,S} \rightarrowμ^+ μ^-)$, are viable compatibly with all other phenomenological constraints.

hep-ph↗

arXiv2021

Collider Signatures of Coannihilating Dark Matter in Light of the B-Physics Anomalies

Motivated by UV explanations of the $B$-physics anomalies, we study a dark sector containing a Majorana dark matter candidate and a coloured coannihilation partner, connected to the Standard Model predominantly via a $U_1$ vector leptoquark. A TeV scale $U_1$ leptoquark, which couples mostly to third generation fermions, is the only successful single-mediator description of the $B$-physics anomalies. After calculating the dark matter relic surface, we focus on the most promising experimental avenue: LHC searches for the coloured coannihilation partner. We find that the coloured partner hadronizes and forms meson-like bound states leading to resonant signatures at colliders reminiscent of the quarkonia decay modes in the Standard Model. By recasting existing dilepton and monojet searches we exclude coannihilation partner masses less than 280 GeV and 400 GeV, respectively. Since other existing collider searches do not significantly probe the parameter space, we propose a new dedicated search strategy for pair production of the coloured partner decaying into $bbττ$ final states and dark matter particles. This search is expected to probe the model up to dark matter masses around 600 GeV with current luminosity.

hep-ph↗

arXiv2021

A Minimal Explanation of Flavour Anomalies: B-Meson Decays, Muon Magnetic Moment, and the Cabibbo Angle

Significant 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 $ϕ^+$. While $S_1$ can provide solutions to charged-current $B$-decays and the muon magnetic moment, and $ϕ^+$ 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.

hep-ph↗

arXiv2019

Exploring the flavour structure of the high-scale MSSM

We analyse the sensitivity of quark flavour-changing observables to the MSSM, in a regime of heavy superpartner masses. We analyse four distinct and motivated frameworks characterising the structure of the soft-breaking terms by means of approximate flavour symmetries. We show that a set of six low-energy observables with realistic chances of improvement in the near future, namely $ΔM_{s,d}$, $ε_K$, $ε_K'/ε_K$, $\mathcal{B} (K\to πν\barν)$, and the phase of $D$--$\bar D$ mixing, could play a very important role in charactering these frameworks in a regime of superpartner masses up to $\mathcal{O}(100)$~TeV. We show that these observables remain very interesting even in a long-term perspective, i.e.~even taking into account the direct mass reach of the most ambitious future high-energy colliders.

hep-ph↗

arXiv2019

B-physics anomalies: The bridge between R-parity violating Supersymmetry and flavoured Dark Matter

In recent years, significant experimental indications that point towards Lepton Flavour Universality violating effects in B-decays, involving $b \to c τν$ and $b \to s \ell^+ \ell^-$ have been accumulated. A possible New Physics explanation can be sought within the framework of R-parity violating Supersymmetry, which contains the necessary ingredients to explain the anomalies via both leptoquark, tree-level exchange and one-loop diagrams involving purely leptonic interactions. In addition, an approximate $U(2)^2$ flavour symmetry, that respects gauge coupling unification, successfully controls the strength of these interactions. Nevertheless strong constraints from leptonic processes and $Z$ boson decays exclude most of the relevant parameter space at the $2 σ$ level. Moreover, R-parity violation deprives Supersymmetry of its Dark Matter candidates. Motivated by these deficiencies, we introduce a new gauge singlet superfield, charged under the flavour symmetry and show that its third-generation, scalar component may participate in loop diagrams that alleviate the above-mentioned tensions, while at the same time reproduce the observed relic abundance. We obtain a solution to both anomalies that is also fully consistent with the rich Flavour and Dark Matter phenomenology. Finally, we assess the prospect to probe the model at future experiments.

hep-ph↗