arXiv subjects

Krzysztof Jodłowski

Publications and source records attributed to Krzysztof Jodłowski.

At least 19 recordsLinked to original sources

arXiv2026

Is a covariant virtual tachyon viable?

Sidney Coleman has noted that superluminal particles or observers would be able to go back in time and have no definite trajectory according to subluminal observers, while not violating Lorentz invariance [1]. Recently, Dragan and Ekert have significantly developed similar ideas even further, which lead to formulation of ``quantum principle of relativity'' that intimately links the two theories [2]. However, field theory descriptions of an on-shell tachyon, described by scalar field $ϕ$ with negative mass squared parameter, lead to violation of basic principles of relativity or quantum mechanics. In this work, we investigate whether purely virtual tachyons can be consistent within the fakeon framework--the only known viable formulation of purely virtual particles. We show that the supports of the real part of the tachyon Feynman propagator, which is also the principal-value propagator (PVP), and the Wheeler propagator intersect only on the light cone. We show that PVP cannot be time-ordered two-point function of a local Hermitian field, excluding the direct extension of the canonical formalism to free fakeon tachyon. Finally, with an imposed tachyonic PVP, interactions with electrons generate composition-dependent accelerations that violate the weak equivalence principle, and we provide a quantitative bound on this scenario. Our analysis identifies obstacles to formulating covariant quantum field theory of interacting virtual tachyon.

hep-ph↗

arXiv2026

Impact of flavor changing processes on prospects for majoron discovery at intensity-frontier searches

The singlet majoron $J$ is the pseudo-Nambu-Goldstone boson of a spontaneously broken global $U(1)_{B-L}$ symmetry that generates Majorana masses for right-handed neutrinos. Its tree-level neutrino coupling scales as $m_ν/f_J$, where $f_J$ is the symmetry-breaking scale, while charged-fermion and gauge-boson couplings, including flavor-changing ones, arise at loop level. Consequently, $J$ can be long-lived over wide regions of parameter space, motivating displaced-decay searches. We study these signatures at proton beam dumps, neutrino facilities, the LHC far detectors, and $Z$ boson factories (including DUNE, NA62, FASER/FASER2, MATHUSLA, SHiP, CEPC, and FCC-ee). We investigate representative positive-semi-definite anarchical, single-flavor, and CP-violating coupling textures, showing that $τ^\pm\to\ell^\pm J$ decays, where $\ell=e,μ$, dominate production in the mass range $m_J\simeq0.2\text{--}1.7\,\mathrm{GeV}$. We find that the combined constraints from BEBC, CHARM, and NuCal are stronger than those from ArgoNeuT, with CEPC and FCC-ee providing a complementary sensitivity to existing flavor-violation searches. Finally, SHiP is expected to provide the strongest constraints, probing effective coupling scales as high as $f\sim 10^9\,\mathrm{GeV}$.

hep-ph↗

arXiv2026

Freeze-in of anapole and charge-radius inelastic dark matter: X-ray probes of a decoupled vector portal

We study freeze-in production and experimental probes of inelastic dark matter (iDM) coupled to the Standard Model through dimension-6 transition anapole and charge-radius operators. These interactions arise upon integrating out the heavy dark photon of a broken $U(1)_D$ vector portal. We focus on mass splittings below the dielectron threshold, where the excited-state decay is cosmologically long-lived and decays predominantly through $χ_1\toχ_0+3γ$, producing a distinctive keV--MeV photon spectrum. We calculate the decay rate and photon spectrum analytically in the Euler--Heisenberg limit and evaluate finite-electron-mass corrections using the full one-loop amplitude. We then combine X-ray limits with freeze-in relic density targets and complementary direct detection (DD) and accelerator constraints. The surviving $χ_1$ population also leads to exothermic downscattering signatures at DD experiments, including the possibility of explaining the LZ signal, while the three-photon decay is constrained by X-ray data. At $Δ=900\,\mathrm{keV}$, INTEGRAL/SPI probes the Boltzmann-suppressed high-mass branches of the freeze-in targets, whereas the NuSTAR limits at $Δ=100\,\mathrm{keV}$ are substantially weaker because of the steep splitting dependence of the decay width. Our results demonstrate the potential of X-ray observations as a probe of freeze-in through a decoupled vector portal and of the reheating temperature governing the iDM production.

hep-ph↗

arXiv2026

Covariant quantum field theory of tachyons is unphysical

Tachyons have fascinated generations of physicists due to their peculiar behavior, but they did not solve any real physical problem. This may have changed with the recent works of Dragan et al., who have shown that superluminal observers may be related to the foundations of quantum mechanics (QM) because they require introducing non-determinism and wave-like behavior at the fundamental level. Unfortunately, we show that the tachyon quantum field theory proposed as a part of this program is not quantum since the tachyon field commutes at all points and the canonical commutations relations of a quantum scalar field are not satisfied. We also discuss other authors' theories, e.g., we show that the Dhar-Sudarshan's formula for the Feynman propagator violates unitarity, and we apply the LSZ formalism to tachyons for the first time, where we find that one cannot prove the LSZ asymptotic condition just by replacing plane waves with wavepackets.

quant-ph↗

arXiv2026

The DAMSA Experiment

DAMSA (DArk Messenger Searches at an Accelerator) is a novel short-baseline accelerator/beam dump experiment aimed at probing short-lived physics processes, including searches for evidence of a dark sector of particle physics and well-motivated rare Standard Model signals. Motivated by open questions in neutrino physics and the absence of conclusive evidence for conventional weakly interacting massive particles, DAMSA targets MeV-to-sub-GeV dark-sector messengers with feeble couplings that can be produced in abundance at a beam dump/target. By employing an ultra-short baseline, DAMSA is uniquely positioned to overcome the beam-dump "ceiling" that limits sensitivity to fast decaying particles in longer-baseline experiments. The conceptual design emphasizes a beam-dump production scheme combined with a compact detector optimized for rare decays while mitigating intense neutron-induced backgrounds, inherent to high-power proton beams. To validate the experimental strategy and detector technologies, the DAMSA Path-Finder (DPF) proof-of-concept experiment is also proposed, focusing on axion-like particles decaying to two photons, as the benchmark physics case and operating with 8 GeV electron beams at SLAC Linac-to-ESA (LESA) facility. Successful realization of DPF will establish the feasibility of the DAMSA approach, enabling a broad and powerful program to explore short-lived new physics and precision Standard Model processes in a previously inaccessible regime. This paper outlines the technical details of DAMSA's physics goals, key experimental challenges, and how to overcome them.

hep-ex↗

arXiv2026

Dark axion portal at $Z$ boson factories

Dark axion portal connects an axion-like-particle (ALP), which can be the QCD axion, with the SM by the coupling to a photon and a dark photon, leading to a rich and distinct phenomenology related to dark matter, astrophysics, and cosmology. We note that due to the gauge invariance, the $Z$ boson-dark photon-ALP coupling should also be generated with sizable strength, and we study its phenomenological consequences at $Z$ boson factories: LEP, FCC-ee, and forward physics detectors at the LHC and FPF@FCC - FASER and MATHUSLA. Due to the large number of $Z$ bosons produced, DAP particles can be efficiently produced and detected by semi-visible displaced decays of the heavier DS species to $γ$+inv. or $f^+ f^-$+inv., and via missing energy signature with zero or one photon. Because of the complementarity of the two approaches, we find great prospects in exploring both short and long-lived lifetime regimes of DAP, especially when the heavier dark species has mass above $0.1\,$GeV.

hep-ph↗

arXiv2026

DAMSA Experiment Conceptual Design White Paper

DAMSA (DArk Messenger Searches at an Accelerator) is a novel short-baseline accelerator experiment aimed at probing short-lived physics processes, including searches for evidence of a dark sector of particle physics and well-motivated Standard Model signals. Motivated by open questions in neutrino physics and the absence of conclusive evidence for conventional weakly interacting massive particles, DAMSA targets MeV-to-sub-GeV dark-sector messengers with feeble couplings that can be produced in abundance at the PIP-II LINAC. By employing an ultra-short baseline of order one meter, DAMSA is uniquely positioned to overcome the beam-dump "ceiling" that limits sensitivity to promptly decaying particles in longer-baseline experiments. The conceptual design emphasizes a beam-dump production scheme combined with a compact detector optimized for rare decays while mitigating intense neutron-induced backgrounds inherent to high-power proton beams. To validate the experimental strategy and detector technologies, the Little DAMSA Path-Finder (LDPF) proof-of-concept experiment is proposed, focusing on axion-like particles decaying to two photons and operating with 300 MeV electron beams at FAST. Successful realization of LDPF will establish the feasibility of the DAMSA approach, enabling a broad and powerful program to explore short-lived new physics and precision Standard Model processes in a previously inaccessible regime. This conceptual design document outlines the technical details of DAMSA's physics goals, the beam facility proposals, key experimental challenges and how to overcome them, and the proposed experimental staging campaigns.

hep-ex↗

arXiv2025

Searches for Power-Law Warped Extra Dimensions

Extra dimensions with a bulk dilaton field can be power-law warped, unlike the exponential warping in the Randall-Sundrum (RS) model. We show that this mildly warped extra dimension can address the hierarchy problem with a novel Kaluza-Klein (KK) spectrum characterized by lighter feebly coupled KK modes compared to the KK modes in the RS model. We investigate the prospects of searching for signatures of such KK modes at current and future colliders, such as the LHC, CLIC, and FCC-ee using visible decays of KK gravitons. We also update the current bounds and projected limits for the RS model and the linear dilaton (LD) model. Furthermore, we explore the long-lived regime of KK gravitons at beam dump experiments, e.g., FASER2, MATHUSLA, and SHiP, as well as constraints from astrophysical and cosmological observations. We find that combining both kinds of searches will enable comprehensive coverage of the model parameter space relevant to the electroweak hierarchy problem.

hep-ph↗

arXiv2024

Probing some photon portals to new physics at intensity frontier experiments

A number of extensions of the Standard Model predict the existence of new light, weakly-coupled particles that couple to the visible sector through higher-dimensional operators containing one or two photons, suppressed by a high new physics scale, and thus have long lifetimes. In this work, we study the prospects for detecting three $\sim\,$sub-GeV such long-lived particles (LLP) at intensity frontier experiments: a massive spin-2 mediator ($G$), a dark axion portal, and a light neutralino coupled to ALPino or gravitino. We consider the production and visible decays of these particles in several current and proposed beam dump experiments (CHARM, NuCal, SeaQuest, NA62, SHiP) as well as in the LHC detectors (FASER, FASER$ν$, FLArE, MATHUSLA). In addition to the usual displaced vertex signature, we also examine the impact of electron scattering signature and the Primakoff-like process which leads to conversion of $G$ into a photon or to the secondary LLP production via upscattering of the lighter dark sector state on dense material put in front of the detector. In all cases, we find the SHiP experiment could provide the strongest constraints for the displaced vertex search, while FASER2/FPF could provide complementary coverage of the $γcτ\sim 1$ m decay length region of the parameter space.

hep-ph↗

arXiv2024

Exploring CP Violation beyond the Standard Model and the PQ Quality with Electric Dipole Moments

In some models of physics beyond the Standard Model (SM), one of the leading low energy consequences of the model appears in the form of the chromo-electric dipole moments (CEDMs) of the gluons and light quarks. We examine if these CEDMs can be distinguished from the QCD $θ$-term through the experimentally measurable nuclear and atomic electric dipole moments (EDMs) in both cases with and without the Peccei-Quinn (PQ) mechanism solving the strong CP problem. We find that the nucleon EDMs show a distinctive pattern when the EDMs are dominantly induced by the light quark CEDMs without the PQ mechanism. In the presence of the PQ mechanism, the QCD $θ$-parameter corresponds to the vacuum value of the axion field, which might be induced either by CEDMs or by UV-originated PQ breaking other than the QCD anomaly, for instance the PQ breaking by quantum gravity effects. We find that in case with the PQ mechanism the nucleon EDMs have a similar pattern regardless of what is the dominant source of EDMs among the CEDMs and $θ$-term, unless there is a significant cancellation between the contributions from different sources. In contrast, some nuclei or atomic EDMs can have characteristic patterns significantly depending on the dominant source of EDMs, which may allow identifying the dominant source among the CEDMs and $θ$-term. Yet, discriminating the gluon CEDM from the QCD $θ$-parameter necessitates additional knowledge of low energy parameters induced by the gluon CEDM, which is not available at the moment. Our results imply that EDMs can reveal unambiguous sign of CEDMs while identifying the origin of the axion vacuum value, however it requires further knowledge of low energy parameters induced by the gluon CEDM.

hep-ph↗

arXiv2023

Indirect detection of long-lived particles in a rich dark sector with a dark vector portal

Simplified models of light new physics provide a convenient benchmark for experimental searches for new physics signatures, including dark matter (DM). However, additional detection modes can arise in less simplified and more realistic scenarios where new degrees of freedom are invoked. In this study, we introduce a non-minimal model based on a popular dark photon portal to DM where the mediator mass is obtained by interactions with the dark Higgs boson which acts as a long-lived particle. We further add to this scenario a new heavy DM species secluded from the Standard Model. In this model, which involves light and heavy particles in the dark sector, we find some new interesting phenomenological features that lead to complementary probes in intensity frontier searches for light long-lived particles, indirect detection searches for dark matter, and cosmic microwave background surveys. We also find possible non-local effects in the DM indirect detection searches that could significantly affect the usual detection strategies.

hep-ph↗

arXiv2023

Looking forward to inelastic DM with electromagnetic form factors at FASER and beam dump experiments

Inelastic Dark Matter (iDM) is an interesting thermal DM scenario that can pose challenges for conventional detection methods. However, recent studies demonstrated that iDM coupled to a photon by electric or magnetic dipole moments can be effectively constrained by intensity frontier experiments using the displaced single-photon decay signature. In this work, we show that by utilizing additional signatures for such models, the sensitivity reach can be increased towards the short-lived regime, $γcτ\sim O(1)\,$m, which can occur in the region of the parameter space relevant to successful thermal freeze-out. These processes are secondary iDM production taking place by upscattering in front of the decay vessel and electron scattering. Additionally, we consider dimension-6 scenarios of photon-coupled iDM - the anapole moment and the charge radius operator - where the leading decay of the heavier iDM state is $χ_1 \to χ_0 e^+ e^-$, resulting in a naturally long-lived $χ_1$. We find that the decays of $χ_1$ at FASER2, MATHUSLA, and SHiP will constrain these models more effectively than the scattering signature considered for the elastic coupling case, while secondary production yields similar constraints as the scattering.

hep-ph↗

arXiv2023

Looking forward to photon-coupled long-lived particles IV: neutralino-ALPino/gravitino

Various supersymmetric (SUSY) scenarios predict a sub-GeV neutralino decaying into a single photon and an invisible state. This signature has recently been studied in a number of intensity frontier experiments, finding constraints complementary to the usual collider searches. In this work, we study the prospects of searches for long-lived neutralinos coupled to an ALPino or gravitino, where each can act as the lightest SUSY particle (LSP). In addition to the neutralino decays into a LSP and a photon, we also consider three-body decays into a pair of charged leptons, and signatures related to scattering with electrons and secondary neutralino production. For both models, we find that the searches at FASER2 will allow to overcome the current bounds, while SHIP will extend these limits by more than an order of magnitude in the value of the coupling constant.

hep-ph↗

arXiv2023

Looking forward to photon-coupled long-lived particles II: dark axion portal

The dark axion portal is a dimension-5 coupling between an axion-like particle (ALP), a photon, and a dark photon, which is one of the targets of the intensity frontier searches looking for $\sim\,$sub-GeV long-lived particles (LLPs). In this work, we re-examine the limits set by existing detectors such as CHARM and NuCal, and by future experiments such as FASER2, MATHUSLA, and SHiP. We extend previous works by i) considering several mass regimes of the Dark Sector (DS) particles, leading to an extended lifetime regime of the unstable species, ii) including LLPs production occurring in previously neglected vector meson decays that actually dominate the LLP yield, and iii) by implementing secondary LLP production. It takes place by Primakoff-like upscattering of lighter DS species into LLP on tungsten layers of neutrino emulsion detector FASER$ν$2. This process will allow FASER2 to cover a significant portion of the $γcτ\sim 1\,m$ region of the parameter space that is otherwise difficult to cover due to the large ($\sim O(100)\,m$) distance between the primary LLP production point and the decay vessel, where LLP decays take place, which is required in typical beam-dumb experiments for SM background suppression.

hep-ph↗

arXiv2021

Self-interacting dark matter from late decays and the $H_0$ tension

We investigate a mechanism for the production of self-interacting dark matter based on WIMP-like messenger state decays into dark matter and dark radiation occurring after recombination. Such a transition leads to a mild relaxation of the Hubble tension, and at the same time may resolve the small-scale structure problems of the $Λ$CDM. We illustrate this mechanism in the Higgs portal dark matter model, which we find to be a promising route.

hep-ph↗

arXiv2021

Neutrino beam-dump experiment with FASER at the LHC

The neutrino physics program at the LHC, which will soon be initiated by the FASER experiment, will provide unique opportunities for precision studies of neutrino interaction vertices at high energies. This will also open up the possibility to search for beyond the standard model (BSM) particles produced in such interactions in the specific high-energy neutrino beam-dump experiment. In this study, we illustrate the prospects for such searches in models with the dipole or $Z^\prime$ portal to GeV-scale heavy neutral leptons. To this end, we employ both the standard signature of new physics that consists of a pair of oppositely-charged tracks appearing in the decay vessel, and the additional types of searches. These include high-energy photons and single scattered electrons. We show that such a variety of experimental signatures could significantly extend the sensitivity reach of the future multi-purpose FASER 2 detector during the High-Luminosity phase of the LHC.

hep-ph↗

arXiv2020

Self-interacting dark matter from late decays and the $H_0$ tension

We study a dark matter production mechanism based on decays of a messenger WIMP-like state into a pair of dark matter particles that are self-interacting via exchange of a light mediator. Its distinctive thermal history allows the mediator to be stable and therefore avoid strong limits from the cosmic microwave background and indirect detection. A natural by-product of this mechanism is a possibility of a late time, i.e., after recombination, transition to subdominant dark radiation component through three-body and one-loop decays to states containing the light mediator. We examine to what extent such a process can help to alleviate the $H_0$ tension. Additionally, the mechanism can provide a natural way of constructing dark matter models with ultra-strong self-interactions that may positively affect the supermassive black hole formation rate. We provide a simple realization of the mechanism in a Higgs portal dark matter model and find a significant region of the parameter space that leads to a mild relaxation of the Hubble tension while simultaneously having the potential of addressing small-scale structure problems of $Λ$CDM.

hep-ph↗

arXiv2020

Extending the reach of FASER, MATHUSLA, and SHiP towards smaller lifetimes using secondary particle production

Many existing or proposed intensity-frontier search experiments look for decay signatures of light long-lived particles (LLPs), highly displaced from the interaction point, in a distant detector that is well-shielded from SM background. This approach is, however, limited to new particles with decay lengths similar to or larger than the baseline of those experiments. In this study, we discuss how this basic constraint can be overcome in BSM models that go beyond the simplest scenarios. If more than one light new particle is present in the model, an additional secondary production of LLPs may take place right in front of the detector, opening this way a new lifetime regime to be probed. We illustrate the prospects of such searches in the future experiments FASER, MATHUSLA and SHiP, for representative models, emphasizing possible connections to dark matter or an anomalous magnetic moment of muon. We also analyze additional advantages from employing dedicated neutrino detectors placed in front of the main decay volume.

hep-ph↗