arXiv subjects

Jure Zupan

Publications and source records attributed to Jure Zupan.

At least 55 records · Page 3Linked to original sources

arXiv2022

Machine Learning and LHC Event Generation

First-principle simulations are at the heart of the high-energy physics research program. They link the vast data output of multi-purpose detectors with fundamental theory predictions and interpretation. This review illustrates a wide range of applications of modern machine learning to event generation and simulation-based inference, including conceptional developments driven by the specific requirements of particle physics. New ideas and tools developed at the interface of particle physics and machine learning will improve the speed and precision of forward simulations, handle the complexity of collision data, and enhance inference as an inverse simulation problem.

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arXiv2022

Theory Techniques for Precision Physics -- Snowmass 2021 TF06 Topical Group Report

The wealth of experimental data collected at laboratory experiments suggests that there is some scale separation between the Standard Model (SM) and phenomena beyond the SM (BSM). New phenomena can manifest itself as small corrections to SM predictions, or as signals in processes where the SM predictions vanish or are exceedingly small. This makes precise calculations of the SM expectations essential, in order to maximize the sensitivity of current and forthcoming experiments to BSM physics. This topical group report highlights some past and forthcoming theory developments critical for maximizing the sensitivity of the experimental program to understanding Nature at the shortest distances.

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arXiv2022

Enhanced neutrino polarizability

We point out that neutrinos can have enhanced couplings to photons, if light (pseudo)scalar mediators are present, resulting in potentially measurable neutrino polarizability. We show that the expected suppression from small neutrino masses can be compensated by the light mediator mass, generating dimension 7 Rayleigh operators at low scales. We explore the rich phenomenology of such models, computing in details the constraints on the viable parameter space, spanned by the couplings of the mediator to neutrinos and photons. Finally, we build several explicit models that lead to enhanced neutrino polarizability by modifying the inverse see-saw majoron, i.e., the pseudo-Nambu-Goldstone boson of the $U(1)_L$ global lepton number responsible for generating small neutrino masses.

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arXiv2022

Self-consistent extraction of spectroscopic bounds on light new physics

Fundamental physical constants are determined from a collection of precision measurements of elementary particles, atoms and molecules. This is usually done under the assumption of the Standard Model~(SM) of particle physics. Allowing for light new physics~(NP) beyond the SM modifies the extraction of fundamental physical constants. Consequently, setting NP bounds using these data, and at the same time assuming the CODATA recommended values for the fundamental physical constants, is not reliable. As we show in this Letter, both SM and NP parameters can be simultaneously determined in a consistent way from a global fit. For light vectors with QED-like couplings, such as the dark photon, we provide a prescription that recovers the degeneracy with the photon in the massless limit, and requires calculations only at leading order in the small new physics couplings. At present, the data show tensions partially related to the proton charge radius determination. We show that these can be alleviated by including contributions from a light scalar with flavor non-universal couplings.

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arXiv2022

TF08 Snowmass Report: BSM Model Building

We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas.

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arXiv2022

Snowmass Theory Frontier: Effective Field Theory

We summarize recent progress in the development, application, and understanding of effective field theories and highlight promising directions for future research. This Report is prepared as the TF02 "Effective Field Theory" topical group summary for the Theory Frontier as part of the Snowmass 2021 process.

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arXiv2022

Dark Sector Physics at High-Intensity Experiments

Is Dark Matter part of a Dark Sector? The possibility of a dark sector neutral under Standard Model (SM) forces furnishes an attractive explanation for the existence of Dark Matter (DM), and is a compelling new-physics direction to explore in its own right, with potential relevance to fundamental questions as varied as neutrino masses, the hierarchy problem, and the Universe's matter-antimatter asymmetry. Because dark sectors are generically weakly coupled to ordinary matter, and because they can naturally have MeV-to-GeV masses and respect the symmetries of the SM, they are only mildly constrained by high-energy collider data and precision atomic measurements. Yet upcoming and proposed intensity-frontier experiments will offer an unprecedented window into the physics of dark sectors, highlighted as a Priority Research Direction in the 2018 Dark Matter New Initiatives (DMNI) BRN report. Support for this program -- in the form of dark-sector analyses at multi-purpose experiments, realization of the intensity-frontier experiments receiving DMNI funds, an expansion of DMNI support to explore the full breadth of DM and visible final-state signatures (especially long-lived particles) called for in the BRN report, and support for a robust dark-sector theory effort -- will enable comprehensive exploration of low-mass thermal DM milestones, and greatly enhance the potential of intensity-frontier experiments to discover dark-sector particles decaying back to SM particles.

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arXiv2022

Accessing CKM suppressed top decays at the LHC

We propose an extension of the existing experimental strategy for measuring branching fractions of top quark decays, targeting specifically $t\to j_q W$, where $j_q$ is a light quark jet. The improved strategy uses orthogonal $b$- and $q$-taggers, and adds a new observable, the number of light-quark-tagged jets, to the already commonly used observable, the fraction of $b$-tagged jets in an event. Careful inclusion of the additional complementary observable significantly increases the expected statistical power of the analysis, with the possibility of excluding $|V_{tb}|=1$ at $95\%$ C.L. at the HL-LHC, and accessing directly the standard model value of $|V_{td}|^2+|V_{ts}|^2$.

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arXiv2022

Snowmass White Paper: New flavors and rich structures in dark sectors

Dark matter can be part of a dark sector with non-minimal couplings to the Standard Model. Compared to many (minimal) benchmark models, such scenarios can result in significant modifications in experimental signatures and strongly impact experimental search sensitivity. In this white paper, we review several non-minimal dark sector models, including phenomenological consequences: models explaining $(g-2)_μ$, inelastic dark matter, strongly interacting massive particles as dark matter candidates, and axions with flavorful couplings. The present exclusions and projected experimental sensitivities on these example dark sector models illustrate the robustness of the growing dark sector experimental effort -- both the broadness and the precision of existing searches -- probing theoretically interesting parameter space. They also illustrate some of the unique complementarity of different experimental approaches.

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arXiv2022

On the implications of positive W mass shift

We investigate the phenomenological implications of the recent $W$ mass measurement by the CDF collaboration, which exhibits tension with the standard model (SM) electroweak fit. Performing the fit to the electroweak observables within the SM effective field theory, we find that the new physics that contributes either to the determination of the electroweak vacuum expectation value, or to the oblique parameters, can improve the agreement with data. The best description is obtained from a fit where flavor universality is not required in the new physics operators, with 2 to 3 $σ$ indications for several nonzero Wilson coefficients. We point out that top partners with order TeV masses could lead to the observed shift in the $W$ mass.

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arXiv2022

Looking forward to Lepton-flavor-violating ALPs

We assess the status of past and future experiments on lepton flavor violating (LFV) muon and tau decays into a light, invisible, axion-like particle (ALP), $a$. We propose a new experimental setup for MEG II, the MEGII-fwd, with a forward calorimeter placed downstream from the muon stopping target. Searching for $μ\to e a$ decays MEGII-fwd is maximally sensitive to LFV ALPs, if these have nonzero couplings to right-handed leptons. The experimental set-up suppresses the (left-handed) Standard Model background in the forward direction by controlling the polarization purity of the muon beam. The reach of MEGII-fwd is compared with the present constraints, the reach of Mu3e and the Belle-II reach from $τ\to \ell a$ decays. We show that a dedicated experimental campaign for LFV muon decays into ALPs at MEG II and Mu3e will be able to probe the ALP parameter space in an unexplored region well beyond the existing astrophysical constraints. We study the implications of these searches for representative LFV ALP models, where the presence of a light ALP is motivated by neutrino masses, the strong CP problem and/or the SM flavor puzzle. To this extent we discuss the majoron in low-scale seesaw setups and introduce the LFV QCD axion, the LFV axiflavon and the leptonic familon, paying particular attention to the cases where the LFV ALPs constitute cold dark matter.

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arXiv2022

Physics reach of a long-lived particle detector at Belle II

We have studied three realistic benchmark geometries for a new far detector GAZELLE to search for long-lived particles at the \superkekb accelerator in Tsukuba, Japan. The new detector would be housed in the same building as Belle II and observe the same $e^+e^-$ collisions. To assess the discovery reach of GAZELLE, we have investigated three new physics models that predict long-lived particles: heavy neutral leptons produced in tau lepton decays, axion-like particles produced in $B$ meson decays, and new scalars produced in association with a dark photon, as motivated by inelastic dark matter. We do not find significant gains in the new physics discovery reach of GAZELLE compared to the Belle II projections for the same final states. The main reasons are the practical limitations on the angular acceptance and size of GAZELLE, effectively making it at most comparable to Belle II, even though backgrounds in the far detector could be reduced to low rates. A far detector for long-lived particles would be well motivated in the case of a discovery by Belle II, since decays inside GAZELLE would facilitate studies of the decay products. Depending on the placement of GAZELLE, searches for light long-lived particles produced in the forward direction or signals of a confining hidden force could also benefit from such a far detector. Our general findings could help guide the design of far detectors at future electron-positron colliders such as the ILC, FCC-ee or CEPC.

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arXiv2022

On $(g-2)_μ$ From Gauged $\mathrm{U}(1)_X$

We investigate an economical explanation for the $(g-2)_μ$ anomaly with a neutral vector boson from a spontaneously broken $\mathrm{U}(1)_X$ gauge symmetry. The Standard Model fermion content is minimally extended by 3 right-handed neutrinos. Using a battery of complementary constraints, we perform a thorough investigation of the renormalizable, quark flavor-universal, vector-like $\mathrm{U}(1)_X$ models, allowing for arbitrary kinetic mixing. Out of 419 models with integer charges not greater than ten, only 7 models are viable solutions, describing a narrow region in model space. These are either $L_μ-L_τ$ or models with a ratio of electron to baryon number close to $-2$. The key complementary constraints are from the searches for nonstandard neutrino interactions. Furthermore, we comment on the severe challenges to chiral $\mathrm{U}(1)_X$ solutions and show the severe constraints on a particularly promising such candidate.

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arXiv2022

Snowmass White Paper: Effective Field Theories for Dark Matter Phenomenology

The quest to discover the nature of dark matter continues to drive many of the experimental and observational frontiers in particle physics, astronomy, and cosmology. While there are no definitive signatures to date, there exists a rich ecosystem of experiments searching for signals for a broad class of dark matter models, at different epochs of cosmic history, and through a variety of processes with different characteristic energy scales. Given the multitude of candidates and search strategies, effective field theory has been an important tool for parametrizing the possible interactions between dark matter and Standard Model probes, for quantifying and improving model-independent uncertainties, and for robust estimation of detection rates in the presence of large perturbative corrections. This white paper summarizes a wide range of effective field theory applications for connecting dark matter theories to experiments.

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arXiv2022

Modeling hadronization using machine learning

We present the first steps in the development of a new class of hadronization models utilizing machine learning techniques. We successfully implement, validate, and train a conditional sliced-Wasserstein autoencoder to replicate the Pythia generated kinematic distributions of first-hadron emissions, when the Lund string model of hadronization implemented in Pythia is restricted to the emissions of pions only. The trained models are then used to generate the full hadronization chains, with an IR cutoff energy imposed externally. The hadron multiplicities and cumulative kinematic distributions are shown to match the Pythia generated ones. We also discuss possible future generalizations of our results.

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arXiv2022

Unleashing the full power of LHCb to probe Stealth New Physics

In this paper, we describe the potential of the LHCb experiment to detect Stealth physics. This refers to dynamics beyond the Standard Model that would elude searches that focus on energetic objects or precision measurements of known processes. Stealth signatures include long-lived particles and light resonances that are produced very rarely or together with overwhelming backgrounds. We will discuss why LHCb is equipped to discover this kind of physics at the Large Hadron Collider and provide examples of well-motivated theoretical models that can be probed with great detail at the experiment.

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arXiv2021

Thermal WIMPs and the Scale of New Physics: Global Fits of Dirac Dark Matter Effective Field Theories

We assess the status of a wide class of WIMP dark matter (DM) models in light of the latest experimental results using the global fitting framework $\textsf{GAMBIT}$. We perform a global analysis of effective field theory (EFT) operators describing the interactions between a gauge-singlet Dirac fermion and the Standard Model quarks, the gluons and the photon. In this bottom-up approach, we simultaneously vary the coefficients of 14 such operators up to dimension 7, along with the DM mass, the scale of new physics and several nuisance parameters. Our likelihood functions include the latest data from $\mathit{Planck}$, direct and indirect detection experiments, and the LHC. For DM masses below 100 GeV, we find that it is impossible to satisfy all constraints simultaneously while maintaining EFT validity at LHC energies. For new physics scales around 1 TeV, our results are influenced by several small excesses in the LHC data and depend on the prescription that we adopt to ensure EFT validity. Furthermore, we find large regions of viable parameter space where the EFT is valid and the relic density can be reproduced, implying that WIMPs can still account for the DM of the universe while being consistent with the latest data.

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arXiv2021

Muonic Force Behind Flavor Anomalies

We develop an economical theoretical framework for combined explanations of the flavor physics anomalies involving muons: $(g-2)_μ$, $R_{K^{(*)}}$, and $b \to s μ^+ μ^-$ angular distributions and branching ratios, that was first initiated by some of us in Ref. [1]. The Standard Model (SM) is supplemented with a lepton-flavored $\mathrm{U}(1)_X$ gauge group. The $\mathrm{U}(1)_X$ gauge boson with the mass of $\mathcal{O}(0.1)$ GeV resolves the $(g-2)_μ$ tension. A TeV-scale leptoquark, charged under the $\mathrm{U}(1)_X$, carries a muon number and mediates $B$-decays without prompting charged lepton flavor violation or inducing proton decay. We explore the theory space of the chiral, anomaly-free $\mathrm{U}(1)_X$ gauge extensions featuring the above scenario, and identify many suitable charge assignments for the SM$+3ν_R$ fermion content with the integer charges in the range $X_{F_i} \in [-10,10]$. We then carry out a comprehensive phenomenological study of the muonic force in representative benchmark models. Interestingly, we found models which can resolve the tension without conflicting the complementary constraints, and all of the viable parameter space will be tested in future muonic resonance searches. Finally, the catalog of the anomaly-free lepton-non-universal charge assignments motivated us to explore different directions in model building. We present a model in which the muon mass and the $(g-2)_μ$ are generated radiatively from a common short-distance dynamics after the $\mathrm{U}(1)_X$ breaking. We also show how to charge a vector leptoquark under $\mathrm{U}(1)_{μ- τ}$ in a complete gauge model.

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