arXiv subjects

Pouya Asadi

Publications and source records attributed to Pouya Asadi.

At least 19 recordsLinked to original sources

arXiv2026

For Whom the Xenon Recoils: Magnetic Inelastic Dark Baryons

We develop a theory of a dark baryon dark matter candidate that interacts with nuclei dominantly through inelastic scattering mediated by a transition magnetic dipole operator. Models are presented that can elegantly explain both the scattering rate and the size of the inelastic splitting to be consistent with the one event observed at LZ\@. Elastic scattering is suppressed due to accidental symmetries within the strongly-coupled sector. The nuclear response is dominated by a spin-dependent structure factor, thus we find a large range of masses, $1 \; {\rm TeV} \lesssim m_\chi \lesssim 50 \; {\rm TeV}$, and mass splitting of $100 \; {\rm keV} \lesssim \delta \lesssim 500 \; {\rm keV}$ can fit the data for a variety of possible dark matter velocity distributions. The models predict that some nuclear scattering events will be accompanied by a simultaneous photon signal with energy $\delta$, which not only distinguishes this model from other inelastic dark matter explanations but also enables directional detection in conventional direct detection experiments. We briefly comment on the dark matter abundance, indirect detection signals (including the models' significantly weaker constraints from dark matter annihilation in the Sun), and the associated collider signals that arise from the meson sector of the theory.

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arXiv2026

Rich Phenomenology from Simple Ingredients: A Review of Confining Dark Sectors

We review theories with confining dark sectors and their implications for dark matter, cosmology, phenomenology, and unsolved Standard Model puzzles. Models with new strongly-coupled non-Abelian gauge interactions can lead to a variety of dark matter candidates (dark mesons, baryons, glueballs, etc.), as well as mechanisms to generate its abundance and symmetries that explain its stability. There are also many potential discovery channels, including direct detection, indirect detection, astrophysical observables, and colliders, as well as correlations between different experiments. We compile a broad conceptual overview of the literature on this topic, aimed at both theorists looking for which questions remain unanswered and experimentalists looking for novel search opportunities. While the theoretical landscape is vast, there are both unifying features and calculational techniques that apply to various regimes. We particularly highlight applications to explaining the similarity of visible and dark matter energy densities, i.e. the $abundance~similarity~puzzle$. We advocate further exploration of this class of theories in the effort to uncover physics beyond the Standard Model.

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arXiv2026

On the Run from the Dark Side of the Muon

We present an analysis strategy for probing physics beyond the Standard Model via modifications to the parton distribution functions (PDFs) in a muon beam, which measurably alter the kinematics of all hard processes at a future muon collider. High-energy muon colliders represent an opportunity to probe new physics using precision measurements and novel search strategies. At sufficiently high energies, light particles act as ``constituents'' of the muon described by PDFs. As a concrete case study, we apply this framework to an $L_{\mu} - L_{\tau}$ gauge boson and demonstrate that, for masses in the range of approximately 50--100 GeV, this indirect PDF-based approach outperforms traditional searches relying on direct gauge boson production. These results highlight muon PDF probes as a powerful and promising avenue for beyond the Standard Model physics searches at a future muon collider.

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arXiv2025

Quirks Live in Cool Universes

We demonstrate that cosmological observations place strong bounds on the reheat temperature $T_\text{RH}$ of the Standard Model (SM) in minimal models of `quirks' -- heavy fermions transforming under the SM gauge group together with a new non-Abelian gauge interaction with a confinement scale far below the mass of the fermions. These models have unique collider signals associated with the confining flux strings, which cannot break due to the large mass of the quirks. Our work shows that in these models $T_\text{RH} \lesssim \mathcal{O}(100)$ GeV for the entire `quirky' parameter space where the effects of the flux string are important. These bounds are in tension with most models of baryogenesis, showing that the discovery of quirks at colliders can have far-reaching implications for cosmology. The bounds arise because the irreducible relic abundance of glueballs from UV freeze-in, combined with their long lifetimes, leads to constraints from the disruption of BBN, distortions of the CMB, excess $\gamma$-rays, an over-abundance of self-interacting dark matter, and contributions to $\Delta N_{\rm eff}$. The glueball freeze-in abundance has a strong dependence on $T_\text{RH}$, making the bounds relatively insensitive to strong interaction uncertainties. The bounds are robust to the SM quantum numbers of the quirks and the presence of Yukawa couplings with the Higgs. In non-minimal extensions of the model where the glueballs can decay to an additional dark sector, the bounds remain for models where the flux string has a macroscopic length at colliders. We also show that for quirk masses above $\sim 10$ TeV, the dark glueballs can be the dominant component of dark matter. This work illustrates a striking connection between quirky collider signals and cosmological probes of new physics, strengthening the case for targeted quirk searches at colliders.

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arXiv2025

Axiverse Baryogenesis

The QCD axion may offer a unified origin for the baryon asymmetry and dark matter through axiogenesis. However, in the minimal QCD axion scenario, axiogenesis either underproduces baryons or overproduces dark matter, and the required kinetic misalignment initial conditions are in tension with axion quality. In this \textit{Letter}, we demonstrate that the axiverse naturally resolves these tensions: the QCD axion emerges as a linear combination of multiple axion-like fields, evading the overclosure problem thanks to new dissipation channels , while introducing additional Peccei--Quinn symmetries that ensure a high quality QCD axion. We illustrate these points in a toy model with two axions. This framework predicts a rich phenomenology within experimental reach, including dark matter detection prospects, astrophysical signals, and collider signatures.

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arXiv2025

MuCol Milestone Report No. 7: Consolidated Parameters

This document is comprised of a collection of consolidated parameters for the key parts of the muon collider. These consolidated parameters follow on from the October 2024 Preliminary Parameters Report. Attention has been given to a high-level consistent set of baseline parameters throughout all systems of the complex, following a 10 TeV center-of-mass design. Additional details of the designs contributing to this baseline design are featured in the appendix. Likewise, explorative variations from this baseline set can be found in the appendix. The data is collected from a collaborative spreadsheet and transferred to overleaf.

physics.acc-ph↗

arXiv2025

Lepton Flavor Violation: From Muon Decays to Muon Colliders

We investigate the unique potential of a high-energy muon collider to probe lepton-flavor-violating signals arising from physics beyond the Standard Model (SM). Low-energy, precision searches for charged lepton-flavor violation (LFV) are projected to dramatically improve their sensitivity in the coming years, and could provide the first evidence of new physics. We interpret the sensitivity of these searches in terms of a set of LFV operators in the SM Effective Field Theory. The same operators are then probed at the TeV scale by evaluating the projected reach of a muon collider while accounting for SM backgrounds and using a parameterized detector simulation. We find that for most operators, a muon collider could confirm signals if they are seen at future low energy experiments, whereas for certain flavor combinations it extends the reach to scales well beyond those accessible at lower energies. We also project the sensitivity of a muon collider to lepton flavor-violating decays of the SM Higgs boson and demonstrate improved sensitivity to $h \to e\tau$ and $h \to \mu\tau$ by an order of magnitude compared to the High-Luminosity LHC. The importance of having multiple, complementary probes is illustrated by considering both various combinations of operators and relative sizes of flavor-violating transitions between generations under various assumptions for the flavor structure of new physics.

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arXiv2025

Stopping Dark Mesons in Their Tracks with Long-Lived Particle and Resonant Signatures

Dark sectors with confining gauge interactions can provide both simple dark matter candidates and striking signals at colliders. We recast Large Hadron Collider searches for two different signatures of dark mesons that arise from a strongly-coupled theory with vector-like dark quarks that are in some non-trivial representation of Standard Model SU(2)$_L$. For any such electroweak representation, there is a 3-plet of dark mesons whose charged components are long-lived, and we reinterpret searches for disappearing tracks to place a lower bound on their mass of $\sim 1.2$ TeV. When the dark quarks are in SU(2)$_L$ representations larger than the fundamental, there is also a 5-plet of dark mesons that interacts with the electroweak gauge bosons via a chiral anomaly. We show that the 5-plet is the unique non-trivial meson multiplet with this anomaly and recast searches for the resulting diboson resonances to place bounds on model parameters. With additional measurements, the anomaly also enables one to reconstruct some ultraviolet parameters (the numbers of dark flavors and colors) while only measuring states in the infrared. Each of these signals represents an exciting opportunity for future searches using higher luminosity.

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arXiv2025

Genesis of baryon and dark matter asymmetries through ultraviolet scattering freeze-in

We introduce a new mechanism for the simultaneous generation of baryon and dark matter asymmetries through ultraviolet-dominated freeze-in scatterings. The mechanism relies on heavy Majorana neutrinos that connect the visible Standard Model sector to a dark sector through the neutrino portal. Following reheating of the visible sector to a temperature well below the heavy neutrino masses, we show that 2-to-2 scattering processes can populate the dark sector and generate both baryon and dark matter asymmetries. In some parameter regions, the dominant source of baryon asymmetry can be charge transfer from the dark sector, a process we call dark wash-in. We also demonstrate that annihilation of the dark matter to massless states within the dark sector can deplete the symmetric population without destroying the net baryon charge to leave only an asymmetric dark matter abundance today. Depending on the specific model parameters, the observed baryon and dark matter abundances can be attained with heavy neutrino masses $M_N \gtrsim 10^{10}$ GeV, and dark matter masses in the range 0.1 GeV $\lesssim m_\chi \lesssim 10^3$ GeV if the dark matter relic abundance is mainly asymmetric and even lower masses if it is symmetric.

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arXiv2025

The Muon Collider

Muons offer a unique opportunity to build a compact high-energy electroweak collider at the 10 TeV scale. A Muon Collider enables direct access to the underlying simplicity of the Standard Model and unparalleled reach beyond it. It will be a paradigm-shifting tool for particle physics representing the first collider to combine the high-energy reach of a proton collider and the high precision of an electron-positron collider, yielding a physics potential significantly greater than the sum of its individual parts. A high-energy muon collider is the natural next step in the exploration of fundamental physics after the HL-LHC and a natural complement to a future low-energy Higgs factory. Such a facility would significantly broaden the scope of particle colliders, engaging the many frontiers of the high energy community. The last European Strategy for Particle Physics Update and later the Particle Physics Project Prioritisation Panel in the US requested a study of the muon collider, which is being carried on by the International Muon Collider Collaboration. In this comprehensive document we present the physics case, the state of the work on accelerator design and technology, and propose an R\&D project that can make the muon collider a reality.

physics.acc-ph↗

arXiv2024

Fermion-Portal Dark Matter at a High-Energy Muon Collider

In this work, we provide a comprehensive study of fermion-portal dark matter models in the freeze-in regime at a future muon collider. For different possible non-singlet fermion portals, we calculate the upper bound on the mediator's mass arising from the relic abundance calculation and discuss the reach of a future muon collider in probing their viable parameter space in prompt and long-lived particle search strategies. In particular, we develop rudimentary search strategies in the prompt region and show that cuts on the invariant dilepton or dijet masses, the missing transverse mass $M_{T2}$, pseudorapidity and energy of leptons or jets, and the opening angle between the lepton or the jet pair can be employed to subtract the Standard Model background. In the long-lived particle regime, we discuss the signals of each model and calculate their event counts. In this region, the lepton-(quark-)portal model signal consists of charged tracks ($R$-hadrons) that either decay in the detector to give rise to a displaced lepton (jet) signature, or are detector stable and give rise to heavy stable charged track signals. As a byproduct, a pipeline is developed for including the non-trivial parton distribution function of a muon component inside a muon beam; it is shown that this leads to non-trivial effects on the kinematic distributions and attainable significances. We also highlight phenomenological features of all models unique to a muon collider and hope our results, for this motivated and broad class of dark matter models, inform the design of a future muon collider detector. We also speculate on suggestions for improving the sensitivity of a muon collider detector to long-lived particle signals in fermion-portal models.

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arXiv2024

Noble Dark Matter: Surprising Elusiveness of Dark Baryons

Dark matter could be a baryonic composite of strongly-coupled constituents transforming under SU(2)$_L$. We classify the SU(2)$_L$ representations of baryons in a class of simple confining dark sectors and find that the lightest state can be a pure singlet or a singlet that mixes with other neutral components of SU(2)$_L$ representations, which strongly suppresses the dark matter candidate's interactions with the Standard Model. We focus on models with a confining $\text{SU}(N_c)$ and heavy dark quarks constituting vector-like $N_f$-plet of SU(2)$_L$. For benchmark $N_c$ and $N_f$, we calculate baryon mass spectra, incorporating electroweak gauge boson exchange in the non-relativistic quark model, and demonstrate that above TeV mass scales, dark matter is dominantly a singlet state. The combination of this singlet nature with the recently discovered $\mathcal{H}$-parity results in an inert state analogous to noble gases, hence we coin the term Noble Dark Matter. Our results can be understood in the non-relativistic effective theory that treats the dark baryons as elementary states, where we find singlets accompanying triplets, 5-plets, or more exotic representations. This generalization of WIMP-like theories is more difficult to find or rule out than dark matter models that include only a single SU(2)$_L$ multiplet (such as a Wino), motivating new searches in colliders and a re-analysis of direct and indirect detection prospects in astrophysical observations.

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arXiv2024

MuCol Milestone Report No. 5: Preliminary Parameters

This document is comprised of a collection of updated preliminary parameters for the key parts of the muon collider. The updated preliminary parameters follow on from the October 2023 Tentative Parameters Report. Particular attention has been given to regions of the facility that are believed to hold greater technical uncertainty in their design and that have a strong impact on the cost and power consumption of the facility. The data is collected from a collaborative spreadsheet and transferred to overleaf.

physics.acc-ph↗

arXiv2024

Direct Detection of Dark Baryons Naturally Suppressed by $\mathcal{H}$-parity

We identify symmetries in a broad class of vector-like confining dark sectors that forbid the leading electromagnetic moments that would ordinarily mediate dark baryon scattering with the Standard Model. The absence of these operators implies dark baryon dark matter has much smaller cross sections for elastic scattering off nuclei, leading to suppressed direct detection signals. In the confined description, we identify an ``$\mathcal{H}$-parity'' symmetry that exists in any dark sector with dark quarks transforming under a vector-like representation of a new confining SU($N_c$) gauge theory as well as a vector-like representation of the electroweak group SU(2)$_L$. The parity is independent of $N_c$ and $N_f$, though it is essential that the dark quarks are neutral under hypercharge. This parity forbids dark hadron electric and magnetic dipole moments, charge radius, and anapole moment, while permitting dimension-7 operators that include polarizability, electroweak loop-induced interactions, as well as lower dimensional electromagnetic $\textit{transition}$ moments between different neutral dark baryon states. We work out an explicit example, $N_c=N_f=3$, that is the most minimal theory with fermionic dark baryons. In this specific model, we use the non-relativistic quark model to show the magnetic dipole moment and charge radius vanish while the transition moments are non-zero, consistent with $\mathcal{H}$-parity. We discuss the implications of a suppressed direct detection signal, emphasizing that this broad class of models provide a well-motivated target for future colliders.

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arXiv2024

A Duet of Freeze-in and Freeze-out: Lepton-Flavored Dark Matter and Muon Colliders

We study a Lepton-Flavored Dark Matter model and its signatures at a future Muon Collider. We focus on the less-explored regime of feeble dark matter interactions, which suppresses the dangerous lepton-flavor violating processes, gives rise to dark matter freeze-in production, and leads to long-lived particle signatures at colliders. We find that the interplay of dark matter freeze-in and its mediator freeze-out gives rise to an upper bound of around TeV scales on the dark matter mass. The signatures of this model depend on the lifetime of the mediator, and can range from generic prompt decays to more exotic long-lived particle signals. In the prompt region, we calculate the signal yield, study useful kinematics cuts, and report tolerable systematics that would allow for a $5σ$ discovery. In the long-lived region, we calculate the number of charged tracks and displaced lepton signals of our model in different parts of the detector, and uncover kinematic features that can be used for background rejection. We show that, unlike in hadron colliders, multiple production channels contribute significantly which leads to sharply distinct kinematics for electroweakly-charged long-lived particle signals. Ultimately, the collider signatures of this lepton-flavored dark matter model are common amongst models of electroweak-charged new physics, rendering this model a useful and broadly applicable benchmark model for future Muon Collider studies that can help inform work on detector design and studies of systematics.

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arXiv2023

Towards a Muon Collider

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.

physics.acc-ph↗

arXiv2023

Wrinkles in the Froggatt-Nielsen Mechanism and Flavorful New Physics

When the Froggatt-Nielsen mechanism is used to explain the Standard Model flavor hierarchy, new physics couplings are also determined by the horizontal symmetry. However, additional symmetries or dynamics in the UV can sometimes lead to a departure from this naïve scaling for the new physics couplings. We show that an effective way to keep track of these changes is by using the new spurions of the $\mathrm{U}(3)^5$ global flavor symmetry, where we parameterize extra suppression or enhancement factors, referred to as wrinkles, using the same power counting parameter as in the original Froggatt-Nielsen model. As a concrete realization, we consider two flavor spurions of the $S_1$ leptoquark, and demonstrate that wrinkles can be used to make an enhanced value of $\textrm{BR}(B^+ \to K^+ν\barν)$ consistent with other flavor observables. We also present example UV models that realize wrinkles, and comment on choosing consistent charges in ordinary Froggatt-Nielsen models without the typical monotonicity condition.

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arXiv2023

Chiral Nelson--Barr Models: Quality and Cosmology

It was recently shown that domain walls from the spontaneous breaking of CP symmetry are exactly stable, and must be inflated away to recover a viable cosmology. We investigate the phenomenological implications of this result in Nelson--Barr solutions of the strong CP problem. Combined with the upper bound on the scale of spontaneous CP breaking necessary to suppress contributions from dangerous, nonrenormalizable operators to $\barθ$, this puts an upper bound on the scale of inflation and the reheating temperature after inflation. Minimal Nelson--Barr models are therefore in tension with thermal leptogenesis, models of large-field inflation, or potential future observations of signals from topological remnants of an unrelated, subsequent phase transition. We study how extending Nelson--Barr models with a new, continuous chiral gauge symmetry can ameliorate this tension by forbidding the dangerous dimension-five operators. In particular, we show that gauging a linear combination of baryon number and hypercharge allows for an economic, anomaly-free extension of the minimal Nelson--Barr model, and discuss the phenomenological implications.

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