arXiv subjects

Gilad Perez

Publications and source records attributed to Gilad Perez.

At least 19 recordsLinked to original sources

arXiv2026

Imperfect axions with no domain wall problem

Post-inflationary axion theories with domain wall number $N>1$ suffer from a domain wall problem. We show analytically, and confirm via simulations, that there is a region of phenomenologically viable parameter space for such theories with additional PQ-violating operators. Contrary to the conventional picture, in such theories the beyond-QCD PQ violation destroys the axion strings before the QCD axion potential becomes cosmologically relevant. This regime is realized for axion decay constants $f_a \lesssim 10^{10} \, \rm GeV$, pointing to a QCD axion mass in the $10^{-3}-10^{-2}\,{\rm eV}$ range. The required additional PQ violation induces a neutron electric dipole moment within two orders of magnitude of the current experimental limit, placing it within the reach of upcoming neutron electric dipole moment experiments.

hep-ph↗

arXiv2026

Probing the electroweak structure of nuclei with rare atoms and molecules

Precision experiments of atoms and molecules have become a powerful probe of the electroweak structure of atomic nuclei and of physics beyond the Standard Model. We review how the interaction between a nucleus and its surrounding bound electrons can be exploited to precisely measure the electromagnetic, parity-violating, and CP-violating properties of nuclei and their fundamental constituents. We focus on rare, unstable isotopes, surveying the experimental techniques and facilities developed in recent years that have extended these measurements to the most exotic regions of the nuclear chart. Recent advances in the precision control and interrogation of single molecules, together with direct laser excitation of nuclear transitions, are opening new frontiers in nuclear and particle physics. At the same time, progress in nuclear theory, machine learning, and high-performance computing is strengthening the connection between our microscopic description of nature and laboratory observables. In many cases, the precision with which nuclear and particle physics properties can be extracted is now limited not by experiment, but by the molecular, atomic, or nuclear theory required to interpret the measurements. This challenge presents a major opportunity for combined theoretical and experimental advances that will enable future discoveries.

physics.atom-ph↗

arXiv2026

Oscillating Imprints of Dark Matter in Mesons Decays

We study scenarios in which ultralight dark matter (ULDM) causes oscillations of the Cabibbo--Kobayashi--Maskawa (CKM) matrix elements, considering two frameworks. The first, previously proposed in the literature, employs the Nelson--Barr mechanism to solve the strong CP problem and the CKM phase is identified with a pseudo-Nambu--Goldstone boson. The second, inspired by Froggatt--Nielsen flavor models, relies on quadratic couplings of the ULDM to the Standard Model while naturally suppressing linear couplings. On the experimental side, we outline a strategy to search for such oscillations at flavor factories using meson decays, focusing on the NA62 experiment as the most promising candidate for discovery thanks to its large kaon statistics. We show that the sensitivity of lifetime-based observables is parametrically degraded when the total particle flux is not known exactly, leading to a substantial loss of sensitivity compared to naive estimates. We therefore advocate alternative observables based on direct counting of events, which retain the expected $1/\sqrt{N}$ scaling and provide a robust probe of oscillating CKM elements. Our results highlight flavor experiments as a novel probe of ULDM through time-dependent signatures.

hep-ph↗

arXiv2026

Probing Ultralight Dark Matter at the Mega-Planck Scale with the Thorium Nuclear Clock

Ultralight dark matter is expected to induce oscillations of nuclear parameters. These oscillations are characterized by extremely weak couplings or high suppression scales, with the Planck scale - the characteristic scale of quantum gravity - serving as a natural benchmark. Probing this phenomenon requires systems with exceptional sensitivity to shifts in nuclear energies. The uniquely low-energy nuclear isomeric transition in ${}^{229}$Th provides such sensitivity: it directly probes the nuclear interaction and, owing to a near cancellation between electromagnetic and nuclear contributions, its response to changes in nuclear structure is greatly amplified. We devise and perform a new type of ultrasensitive search for dark matter which uses the precision nuclear spectroscopy at JILA to set the strongest bounds in the mass range $10^{-21}\,{\rm eV} \lesssim m_{\rm DM} \lesssim 10^{-19}\,{\rm eV}$. Our results probe effective interaction scales exceeding $10^6$ times the Planck scale (the Mega-Planck scale) and establish the ${}^{229}$Th system as the leading probe of dark matter couplings to the nuclear sector.

hep-ph↗

arXiv2026

Is the Conventional Picture of Coherence Time Complete? Dark Matter Recoherence

The local solar gravitational potential forms a basin for ultralight dark matter (ULDM), with discrete energy levels. Even if barely populated, it introduces a new characteristic timescale in DM dynamics. This necessitates a generalization of the notion of coherence time. We find that, at long times, the phenomenon of recoherence emerges, whereby a subcomponent of ULDM exhibits a formally divergent coherence time. The fact that this generalized coherence time can significantly exceed the naive estimate implies an enhanced sensitivity for dark matter searches that accumulate data over extended observation periods.

hep-ph↗

arXiv2025

Search for a solar-bound axion halo using the Global Network of Optical Magnetometers for Exotic physics searches

We report on a search for a gravitationally bound solar axion halo using data from the Global Network of Optical Magnetometers for Exotic physics searches (GNOME), a worldwide array of magnetically shielded atomic magnetometers with sensitivity to exotic spin couplings. Motivated by recent theoretical work suggesting that self-interacting ultralight axions can be captured by the Sun's gravitational field and thermalize into the ground state, we develop a signal model for the pseudo-magnetic fields generated by axion-proton gradient couplings in such a halo. The analysis focuses on the fifth GNOME Science Run (69 days, 12 stations), employing a cross-correlation pipeline with time-shifted daily modulation templates to search for the global, direction-dependent, monochromatic signal expected from a solar axion halo. No statistically significant candidate signals are observed. We set 95% confidence-level upper limits on the amplitude of the axion-induced pseudo-magnetic field over the frequency range $\approx 0.05-20$ Hz, translating to constraints on the linear and quadratic axion-proton couplings for halo densities predicted by gravitational capture models and for the maximum overdensities allowed by planetary ephemerides. In the quadratic coupling case, our limits surpass existing astrophysical bounds by over two orders of magnitude across much of the accessible parameter space.

physics.atom-ph↗

arXiv2025

Effective Field Theory Perspective On King Non-linearity

Precision spectroscopic measurements of isotope shifts have recently reached a high level of accuracy. Tests of King non-linearity (NL) along isotope chains have been proposed as a tool to search for fifth-force mediators. At the same time, these tests can potentially teach us about the structure of heavy nuclei at unprecedented precision, where King NL has already been observed in several systems. A robust interpretation of the existing data, however, is hampered by incomplete control over the Standard Model (SM) contributions. We develop a systematic effective field theory framework, matching the SM onto scalar non-relativistic QED in the infinite nuclear mass limit and then onto quantum-mechanical potentials. This approach organizes all nuclear effects into a small set of Wilson coefficients and cleanly separates short- and long-distance physics. We show that the commonly used treatment of the $\langle r^2\rangle^2$ term needs to be reconsidered, as it arises only at second-order in perturbation theory, and we derive the long-range $1/r^4$ potential from nuclear polarizability. Applying the framework to hydrogen-like systems, we provide a transparent classification of SM sources of King NL relevant for current and future isotope-shift experiments. The formalism can be applied to learn about the shape of the heavy scalar nuclei at a higher level of precision and detail than what was previously attainable.

hep-ph↗

arXiv2025

Natural Ultralight Dark Matter: The Quadratic Twin

Scalar ultralight dark matter (ULDM) is uniquely accessible to tabletop experiments such as clocks and interferometers, and its search has been the focus of a vast experimental effort. However, the scalar ULDM mass is not protected from radiative corrections, and the entirety of the parameter space within reach of experiments suffers from a severe naturalness problem. In this paper, we propose a new twin mechanism that protects the mass of the scalar ULDM. Our scalar ULDM is a pseudo-Nambu-Goldstone boson with quadratic couplings to the Standard Model (SM) and to a twin copy of the SM, with a mirror $\mathbb{Z}_2$ symmetry exchanging each SM particle with its twin. Due to the mirror symmetry, the leading-order mass correction is quadratic in the (tiny) coupling while the linear order is canceled. This opens up vast regions of parameter space for natural quadratically coupled ultralight dark matter, within the sensitivity of existing and future experiments.

hep-ph↗

arXiv2025

Probing New Forces with Nuclear Clocks

Clocks based on nuclear isomer transitions promise exceptional stability and precision. The low transition energy of the thorium-229 isomer makes it an ideal candidate, as it has been excited by a vacuum-ultraviolet laser and is highly sensitive to subtle interactions. This enables the development of powerful tools for probing new forces, which we call {\it quintessometers}. In this work, we demonstrate the potential of nuclear clocks, particularly solid-state variants, to surpass existing limits on scalar field couplings, exceeding the sensitivity of current fifth-force searches at submicron distances and significantly improving equivalence-principle tests at kilometer scales and beyond. Additionally, we highlight the capability of transportable nuclear clocks to detect scalar interactions at distances beyond $10\,$km, complementing space-based missions.

hep-ph↗

arXiv2025

Momentum and Matter Matter for Axion Dark Matter Matters on Earth

We investigate the implications of matter effects to searches for axion Dark Matter on Earth. The finite momentum of axion Dark Matter is crucial to elucidating the effects of Earth on both the axion Dark Matter field value and its gradient. We find that experiments targeting axion couplings compatible with canonical solutions of the strong CP puzzle are likely not affected by Earth's matter effects. However, experiments sensitive to lighter axions with stronger couplings can be significantly affected, with a significant part of the parameter space suffering from a reduced axion field value, and therefore decreased experimental sensitivity. In contrast, the spatial gradient of the axion field can be enhanced along Earth's radial direction, with important implications for ongoing and planned experiments searching for axion Dark Matter.

hep-ph↗

arXiv2024

Searching for hadronic scale baryonic and dark forces at $(g-2)_\mu$'s lattice-vs-dispersion front

The anomalous magnetic moment of the muon ($\,a_{\mu}\,$) provides a stringent test of the quantum nature of the Standard Model (SM) and its extensions. To probe beyond the SM physics, one needs to be able to subtract the SM contributions, which consists of a non-perturbative part, namely, the hadronic vacuum polarization (HVP) of the photon. The state of the art is to predominantly use two different methods to extract this HVP: lattice computation, and dispersion relation-based, data-driven method. Thus one can construct different forms of the ``$a_{\mu}$ test" which compares the precise measurement of $a_{\mu}$ to its theory prediction. Additionally, this opens the possibility for another subtle test, where these two ``theory" predictions themselves are compared against each other, which is denoted as the ``HVP-test". This test is particularly sensitive to hadronic scale new physics. Therefore, in this work, we consider a SM extension consisting of a generic, light $\sim(100~{\rm MeV}-1~{\rm GeV})$ vector boson and study its impact on both tests. We develop a comprehensive formalism for this purpose. We find that in the case of data-driven HVP being used in the $a_{\mu}$ test, the new physics contributions effectively cancels for a flavor-universal vector boson. As an illustration of these general results, we consider two benchmark models: i)~the dark photon ($\,A'\,$) and ii)~a gauge boson coupled to baryon-number ($\,B\,$). Using a combination of these tests, we are able to constrain the parameter space of $B$ and $A'$, complementarily to the existing limits. As a spin-off, our preliminary analysis of the spectrum of invariant mass of $3\pi$ in events with ISR at the $B-$ factories (BaBar, Belle) manifests the value of such a study in searching for $B\to 3\pi$ decay, thus motivating a dedicated search by experimental collaborations.

hep-ph↗

arXiv2024

On the sensitivity of nuclear clocks to new physics

The recent demonstration of laser excitation of the $\approx 8$ eV isomeric state of Thorium-229 is a significant step towards a nuclear clock. The low excitation energy likely results from a cancellation between electromagnetic and strong contributions, which new physics can disrupt. In this Letter, we quantify the enhancement of a nuclear clock's sensitivity to new physics using a geometric model and a novel $d$-wave halo model of the nucleus that reproduces measured differences between Thorium-229 states. We find likely enhancements of order $10^4$ while a worst case scenario with enhancement $\ll 1$ is unlikely.

hep-ph↗

arXiv2024

Searching for dark matter with the Th-229 nuclear lineshape from laser spectroscopy

The recent laser excitation of the low-lying Th-229 isomer transition is starting a revolution in ultralight dark matter searches. The enhanced sensitivity of this transition to the large class of dark matter models dominantly coupling to quarks and gluons will ultimately allow us to probe coupling strengths eight orders of magnitude smaller than the current bounds from optical atomic clocks, which are mainly sensitive to dark matter couplings to electrons and photons. We argue that, with increasing precision, observations of the Th-229 excitation spectrum will soon give world-leading constraints. Using data from the pioneering laser excitation of Th-229 by Tiedau et al. [Phys. Rev. Lett. 132, 182501 (2024)], we present a first dark matter search in the excitation spectrum. While the exclusion limits of our detailed study of the lineshape are still below the sensitivity of currently operating clock experiments, we project the measurement of Zhang et al. [Nature 663, 63 (2024)] to surpass it.

hep-ph↗

arXiv2024

Nelson-Barr ultralight dark matter

We show that, in the Nelson-Barr solution to the strong CP-problem, a naturally light scalar can arise. It gives rise to a completely new phenomenology beyond that of the celebrated QCD axion, if this field constitutes dark matter, as the CKM elements vary periodically in time. We also discuss how the model can be tested using quantum sensors, in particular using nuclear clocks, which leads to an interesting synergy between different frontiers of physics.

hep-ph↗

arXiv2024

Lorentz violating backgrounds from quadratic, shift-symmetric, ultralight dark matter

We consider an effective theory for a shift-symmetric, quadratically-coupled, ultralight spin-0 field. The leading CP-conserving interactions with Standard Model fields in the effective theory arise at dimension 8. We discuss the renormalization group evolution and positivity bounds on these operators, as well as their possible UV origins. Assuming that the spin-0 field is associated with an ultralight dark matter candidate, we discuss the effects of the dimension-8 operators on experiments searching for the oscillation of fundamental constants and Lorentz violation. We find that the direct bounds on these two effects are of similar strength but rather weak, corresponding to a UV cutoff scale of keV order, as they are mediated by dimension-8 operators.

hep-ph↗

arXiv2024

Prospects of nuclear-coupled-dark-matter detection via correlation spectroscopy of I$_2^+$ and Ca$^+$

The nature of dark matter (DM) and its interaction with the Standard Model (SM) is one of the biggest open questions in physics nowadays. The vast majority of theoretically-motivated Ultralight-DM (ULDM) models predict that ULDM couples dominantly to the SM strong/nuclear sector. This coupling leads to oscillations of nuclear parameters that are detectable by comparing clocks with different sensitivities to these nature's constants. Vibrational transitions of molecular clocks are more sensitive to a change in the nuclear parameters than the electronic transitions of atomic clocks. Here, we propose the iodine molecular ion, I$_2^+$, as a sensitive detector for such a class of ULDM models. The iodine's dense spectrum allows us to match its transition frequency to that of an optical atomic clock (Ca$^+$) and perform correlation spectroscopy between the two clock species. With this technique, we project a few-orders-of-magnitude improvement over the most sensitive clock comparisons performed to date. We also briefly consider the robustness of the corresponding "Earth-bound" under modifications of the $Z_N$-QCD axion model.

physics.atom-ph↗

arXiv2024

A Note on the Quality of Dilatonic Ultralight Dark Matter

Dilatons are pseudo-Nambu-Goldstone bosons arising from the breaking of conformal invariance. In this letter we point out that in general a dilaton mass has a power-law dependence on a small parameter related to the explicit breaking of conformal invariance whereas the ratio between the ultraviolet and infrared scales in the theory are exponentially related to the same parameter. We show that this scaling results in a separation between the dilaton mass and the infrared scale that can not be arbitrary large. Therefore a small dilaton mass necessarily is associated to a secluded conformal sector. We argue that the fact that the dilaton field must have a small displacement from the minimum of its effective potential generated near the infrared scale precludes a cosmologically interesting amount of dilatonic dark matter to be produced by a misalignment mechanism in the early Universe.

hep-ph↗

arXiv2024

Oscillations of atomic energy levels induced by QCD axion dark matter

Axion-gluon interaction induces quadratic couplings between the axion and the matter fields. We find that, if the axion is an ultralight dark matter field, it induces small oscillations of the mass of the hadrons as well as other nuclear quantities. As a result, atomic energy levels oscillate. We use currently available atomic spectroscopy data to constrain such axion-gluon coupling. We also project the sensitivities of future experiments, such as ones using molecular and nuclear clock transitions. We show that current and near-future experiments constrain a finely-tuned parameter space of axion models. These can compete with or dominate the already-existing constraints from oscillating neutron electric dipole moment and supernova bound, in addition to those expected from near future magnetometer-based experiments. We also briefly discuss the reach of accelerometers and interferometers.

hep-ph↗