arXiv subjects

Martin A. Mojahed

Publications and source records attributed to Martin A. Mojahed.

12 recordsLinked to original sources

arXiv2026

Minimal spontaneous baryogenesis from flavor

In its minimal realization, the Froggatt-Nielsen (FN) mechanism addresses the Standard Model (SM) flavor puzzle via the spontaneous breaking of a horizontal $U(1)_H$ symmetry. If $U(1)_H$ is global and broken before the end of inflation, it gives rise to a pseudo-Nambu-Goldstone boson (axion-like particle) with a homogeneous initial misalignment, whose subsequent coherent evolution sources spontaneous $CPT$ violation in the SM sector. We show that in the presence of $B-L$-violating processes $-$ parametrized here model-independently via the dimension-five Weinberg operator responsible for light neutrino masses $-$ the minimal FN setup can generate the baryon asymmetry of the Universe (BAU), linking the origin of flavor directly to the BAU and neutrino masses. Solving a complete set of evolution equations for SM asymmetries, we demonstrate that this mechanism can readily yield a baryon asymmetry comparable to the observed value, or even exceeding it by several orders of magnitude. Accounting for baryonic isocurvature and entropy dilution from axion decays, we find that the observed BAU is successfully reproduced for axion oscillation temperatures above $10^{11}$ GeV and axion decay constants ranging from $10^{13\cdots 14}$ GeV to above $10^{17}$ GeV. Finally, while we focus on a global $U(1)_H$ symmetry and axion motion from standard misalignment, our framework is readily extendable to other global horizontal symmetries and arbitrary axion motion.

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arXiv2026

Axion-driven spontaneous leptogenesis, precisely

We revisit a minimal scenario for spontaneous leptogenesis where the asymmetry generation is driven by a heavy axion-like field evolving via standard misalignment. We focus on the simplest framework in which lepton number violation originates from the dimension-five Weinberg operator and contributions from standard thermal leptogenesis become negligible. The asymmetry is computed by solving a set of transport equations, which incorporate fully flavor-dependent interaction rates for the Weinberg operator that are presented here for the first time. We also derive a simple algebraic master formula for the generated $B\!-\!L$ asymmetry, valid for arbitrary axion velocities and classically shift-symmetric couplings to the Standard Model, that reproduces the $B\!-\!L$-production dynamics of the full set of transport equations in controlled parameter regions. Along the way, we quantify the importance of low-scale neutrino masses and the two mass orderings on the final prediction for the generated asymmetry. Finally, we assess the cosmological viability of different axion couplings by accounting for entropy dilution from late-time axion decays and imposing constraints from baryonic isocurvature perturbations. We demonstrate that explaining the baryon asymmetry via standard Majoron misalignment is under severe tension due to dilution from late-time decays. In contrast, axions coupled to strong or weak sphalerons can successfully produce the observed asymmetry for decay constants near the energy scale of grand unification and axion oscillation temperatures $T_{\text{osc}} \gtrsim 10^{11\cdots12}$ GeV, provided a cosmological history featuring high-scale inflation and efficient reheating.

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arXiv2026

Asymgenesis

We present a framework based on the standard type-I seesaw model that relates the baryon asymmetry of the universe to the dark matter (DM) density. The framework, which we name "Asymgenesis", relies on the presence of primordial charge asymmetries seeded either in the dark sector or in the visible sector. A higher-dimensional portal operator reshuffles this initial asymmetry into both sectors, eventually resulting in a nonzero $B-L$ asymmetry and an asymmetric DM component. Compared to conventional asymmetric-dark-matter (ADM) schemes, our framework imposes far milder requirements on the portal interaction. In particular, the portal interaction need not violate $B-L$, and the temperature scales of efficient $B-L$ violation and efficient charge-transfer interaction mediated by the portal operator can be separated. We develop the formalism in detail and argue that the flexibility of our framework enlarges the model-building landscape for ADM.

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arXiv2025

Freeze-in leptogenesis without the need for right-handed neutrino oscillations

We present an experimentally testable leptogenesis mechanism based on the standard type-I seesaw model that successfully operates at right-handed-neutrino (RHN) masses around the GeV scale. The mechanism takes place in a cosmological background with an asymmetry between right-handed electrons and left-handed positrons generated at high temperatures, and does not require oscillations between RHNs or any CP violation in the RHN sector. In contrast to standard leptogenesis via freeze-in, our mechanism works even in the presence of a single RHN around the GeV scale. The mechanism is illustrated for the minimal type-I seesaw with two RHNs, where we show that successful baryogenesis via leptogenesis is viable in large regions of parameter space even without a small mass splitting between the RHNs.

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arXiv2025

A lower bound on the right-handed neutrino mass from wash-in leptogenesis

Leptogenesis is an attractive scenario for the generation of the baryon asymmetry of the Universe that relies on the dynamics of right-handed neutrinos (RHNs) in the seesaw extension of the Standard Model. In standard thermal leptogenesis, the RHN mass scale $M_N$ is subject to the Davidson--Ibarra bound, $M_N \gtrsim 10^9\,\textrm{GeV}$, which builds on the assumption that RHN decays are responsible for the violation of both charge-parity invariance ($CP$) and baryon-minus-lepton number ($B\!-\!L$). In this paper, we relax this assumption in the context of the more flexible framework of wash-in leptogenesis, in which $CP$ violation is encoded in the initial conditions and the only remaining task of the RHN decays is to violate $B\!-\!L$. Solving the relevant set of Boltzmann equations for vanishing initial baryon and lepton numbers (i.e., $B = L_e = L_μ= L_τ= 0$ initially), we find that, in wash-in leptogenesis, the RHN mass scale can be as low as 7~TeV. Wash-in leptogenesis at such low RHN masses requires the presence of a primordial charge asymmetry between right-handed electrons and left-handed positrons. We discuss several possibilities for the origin of such an asymmetry and comment on its implications for the chiral instability of the Standard Model plasma.

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arXiv2025

Gravitational charge production

Wash-in leptogenesis is an attractive mechanism to produce the baryon asymmetry of the Universe. It treats right-handed-neutrino interactions as spectator processes, on the same footing as electroweak sphalerons, that reprocess primordial charge asymmetries in the thermal plasma into a baryon-minus-lepton asymmetry. The origin of these primordial charges must be accounted for by new $CP$-violating dynamics at very high energies. In this paper, we propose such a scenario of chargegenesis that, unlike earlier proposals, primarily relies on new interactions in the gravitational sector. We point out that a coupling of a conserved current to the divergence of the Ricci scalar during reheating can lead to nonzero effective chemical potentials in the plasma that, together with a suitable charge-violating interaction, can result in the production of a primordial charge asymmetry. Gravitational chargegenesis represents a substantial generalization of the idea of gravitational baryogenesis. We provide a detailed analysis of a generic and minimal realization that is consistent with inflation and show that it can successfully explain the baryon asymmetry of the Universe.

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arXiv2025

Graviton- and Inflaton-mediated Dark Matter Production after Large Field Polynomial Inflation

Polynomial inflation is a simple cosmological scenario, which fits the cosmic microwave background data well. It provides testable predictions for the tensor-to-scalar ratio and the running of the spectral index. In this work, we investigate the production of Dirac dark matter (DM) within the framework of large-field polynomial inflation. We study all relevant production channels including $i$) non-thermal production through inflaton decays and scatterings, and $ii$) thermal production from scattering of standard model particles mediated by inflatons and gravitons. In contrast to small-field polynomial inflation, where inflaton decay dominates DM production, we find that graviton-mediated processes can be dominant in the large-field scenario. For DM lighter than the inflaton, we demonstrate that the interplay between graviton- and inflaton-mediated production channels give rise to non-trivial relations between the DM mass and the reheating temperature required to account for the DM relic abundance.

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arXiv2024

Disentangling new physics in $K\rightarrowπ\barνν$ and $B\rightarrow K(K^*)\barνν$ observables

We investigate the possibility of disentangling different new physics contributions to the rare meson decays $K\rightarrowπ+\displaystyle{\not}E$ and $B\rightarrow K(K^*)+\displaystyle{\not}E$ through kinematic distributions in the missing energy $\displaystyle{\not}E$. We employ dimension-$6$ operators within the Low-Energy Effective Field Theory (LEFT), identifying the invisible part of the final state as either active or sterile neutrinos. Special emphasis is given to lepton-number violating (LNV) operators with scalar and tensor currents. We show analytically that contributions from scalar, vector, and tensor quark currents can be uniquely determined from experimental data of kinematic distributions. In addition, we present new correlations of branching ratios for $K$ and $B$-decays involving scalar and tensor currents. As there could a priori also be new invisible particles in the final states, we include dark-sector operators giving rise to two dark scalars, fermions, or vectors in the final state. In this context, we present new calculations of the inclusive decay rate $B\rightarrow X_s+\displaystyle{\not}E$ for dark operators. We show that careful measurements of kinematic distributions make it theoretically possible to disentangle the contribution from LEFT operators from most of the dark-sector operators, even when multiple operators are contributing. We revisit sum rules for vector currents in LEFT and show that the latter are also satisfied in some new dark-physics scenarios that could mimic LEFT. Finally, we point out that an excess in rare meson decays consistent with a LNV hypothesis would point towards highly flavor non-democratic physics in the UV, and could put high-scale leptogenesis under tension.

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arXiv2022

On-Shell Recursion Relations for Nonrelativistic Effective Field Theories

We derive on-shell recursion relations for nonrelativistic effective field theories (EFTs) with enhanced soft limits. The recursion relations are illustrated through analytic calculation of tree-level scattering amplitudes in theories with a complex Schrödinger-type field, real scalar with linear dispersion relation, and real scalar with Lifshitz-type dispersion relation. Our results show that the landscape of gapless nonrelativistic EFTs with local $S$-matrix can be constrained by soft theorems and the consistency of the low-energy $S$-matrix similarly to massless relativistic EFTs.

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arXiv2022

Nonrelativistic effective field theories with enhanced symmetries and soft behavior

We systematically explore the landscape of nonrelativistic effective field theories with a local $S$-matrix and enhanced symmetries and soft behavior. The exploration is carried out using both conventional quantum field theory methods based on symmetry arguments, and recently developed on-shell recursion relations. We show that, in contrary to relativistic theories, enhancement of the soft limit of scattering amplitudes in nonrelativistic theories is generally not a byproduct of symmetry alone, but requires additional low-energy data. Sufficient conditions for enhanced scattering amplitudes can be derived by combining symmetries and dispersion relations of the scattered particles. This has direct consequences for the infrared dynamics that different types of nonrelativistic Nambu-Goldstone bosons can exhibit. We then use a bottom-up soft bootstrap approach to narrow down the landscape of nonrelativistic effective field theories that possess a consistent low-energy $S$-matrix. We recover two exceptional theories of a complex Schrödinger-type scalar, namely the $\mathbb{C} P^1$ nonlinear sigma model and the Schrödinger-Dirac-Born-Infeld theory. Moreover, we use soft recursion to prove a no-go theorem ruling out the existence of other exceptional Schrödinger-type theories. We also prove that all exceptional theories of a single real scalar with a linear dispersion relation are necessarily Lorentz-invariant. Soft recursion allows us to obtain some further general bounds on the landscape of nonrelativistic effective theories with enhanced soft limits. Finally, we present a novel theory of a complex scalar with a technically natural quartic dispersion relation. Altogether, our work represents the first step of a program to extend the developments in the study of scattering amplitudes to theories without Lorentz invariance.

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arXiv2021

Quark, pion and axial condensates in three-flavor finite isospin chiral perturbation theory

We calculate the light quark condensate, the strange quark condensate, the pion condensate, and the axial condensate in three-flavor chiral perturbation theory ($χ$PT) in the presence of an isospin chemical potential at next-to-leading order at zero temperature. It is shown that the three-flavor $χ$PT effective potential and condensates can be mapped onto two-flavor $χ$PT ones by integrating out mesons with strange quark content (kaons and eta), with renormalized couplings. We compare the results for the light quark and pion condensates at finite pseudoscalar source with ($2+1$)-flavor lattice QCD, and we also compare the axial condensate at zero pseudoscalar and axial sources with lattice QCD data. We find that the light quark, pion, and axial condensates are in very good agreement with lattice data. There is an overall improvement by including NLO effects.

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arXiv2021

Condensates and pressure of two-flavor chiral perturbation theory at nonzero isospin and temperature

We consider two-flavor chiral perturbation theory ($χ$PT) at finite isospin chemical potential $μ_I$ and finite temperature $T$. We calculate the effective potential and the quark and pion condensates as functions of $T$ and $μ_I$ to next-to-leading order in the low-energy expansion in the presence of a pionic source. We map out the phase diagram in the $μ_I$--$T$ plane. Numerically, we find that the transition to the pion-condensed phase is second order in the region of validity of $χ$PT, which is in agreement with model calculations and lattice simulations. Finally, we calculate the pressure to two-loop order in the symmetric phase for nonzero $μ_I$ and find that $χ$PT seems to be converging very well.

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