arXiv subjects

Martti Raidal

Publications and source records attributed to Martti Raidal.

At least 37 records · Page 2Linked to original sources

arXiv2021

Higgs-like spectator field as the origin of structure

We show that the observed primordial perturbations can be entirely sourced by a light spectator scalar field with a quartic potential, akin to the Higgs boson, provided that the field is sufficiently displaced from vacuum during inflation. The framework relies on the indirect modulation of reheating, which is implemented without any direct coupling between the spectator field and the inflaton and does not require non-renormalisable interactions. The scenario gives rise to local non-Gaussianity with $f_{\rm NL}\simeq 5$ as the typical signal. As an example model where the indirect modulation mechanism is realised for the Higgs boson, we study the Standard Model extended with right-handed neutrinos. For the Standard Model running we find, however, that the scenario analysed does not seem to produce the observed perturbation.

hep-ph↗

arXiv2021

A fake doublet solution to the muon anomalous magnetic moment

Extensions to the Standard Model that use strictly off-shell degrees of freedom - the fakeons - allow for new measurable interactions at energy scales usually precluded by the constraints that target the on-shell propagation of new particles. Here we employ the interactions between a new fake scalar doublet and the muon to explain the recent Fermilab measurement of its anomalous magnetic moment. Remarkably, unlike in the case of usual particles, the experimental result can be matched for fakeon masses below the electroweak scale without contradicting the stringent precision data and collider bounds on new light degrees of freedom. Our analysis, therefore, demonstrates that the fakeon approach offers unexpected viable possibilities to model new physics naturally at low scales.

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arXiv2021

Cosmological black holes are not described by the Thakurta metric: LIGO-Virgo bounds on PBHs remain unchanged

We show that the physical conditions which induce the Thakurta metric, recently studied by Bœhm {\it et al.} in the context of time-dependent black hole masses, correspond to a single accreting black hole in the entire Universe filled with isotropic non-interacting dust. In such a case, the physics of black hole accretion is not local but tied to the properties of the whole Universe. We show that radiation, primordial black holes or particle dark matter cannot produce the specific energy flux required for supporting the mass growth of Thakurta black holes. In particular, this solution does not apply to black hole binaries. We conclude that cosmological black holes and their mass growth cannot be described by the Thakurta metric, and thus existing constraints on the primordial black hole abundance from the LIGO-Virgo and the CMB measurements remain valid.

astro-ph.CO↗

arXiv2021

An effective field theory of the Delta-resonance

We present an effective field theory of the $Δ$-resonance as an interacting Weinberg's $(3/2,0)\oplus (0,3/2)$ field in the multi-spinor formalism. We derive its interactions with nucleons $N$, pions $π$ and photons $γ$, and compute the $Δ$-resonance cross-sections in pion-nucleon scattering and pion photo-production. The theory contains only the physical spin-3/2 degrees of freedom. Thus, it is intrinsically consistent at the Hamiltonian level and, unlike the commonly used Rarita-Schwinger framework, does not require any additional ad hoc manipulation of couplings or propagators. The symmetries of hadronic physics select a unique operator for each coupling $NπΔ$ and $γπΔ$. The proposed framework can be extended to also describe other higher-spin hadronic resonances.

hep-ph↗

arXiv2021

Reply to "Comment on: Cosmological black holes are not described by the Thakurta metric"

In this reply, we address the comment [arXiv:2105.14908] to our recent paper [arXiv:2105.09328], where we argued that the Thakurta metric does not describe cosmological black holes. We clarify that the mass growth of Thakurta black holes is due to an influx of energy (i.e. accretion), which, by definition, is not a feature of geometry. The conclusions of [arXiv:2105.09328] are independent of the interpretation of this energy flux. We show that the average energy density of primordial Thakurta black holes scales as $a^{-2}$ and requires an unrealistic and fine-tuned energy transfer from a smooth dark matter component to the primordial black hole sector.

astro-ph.CO↗

arXiv2021

Higher-spin particles at high-energy colliders

Using an effective field theory approach for higher-spin fields, we derive the interactions of colour singlet and electrically neutral particles with a spin higher than unity, concentrating on the spin-3/2, spin-2, spin-5/2 and spin-3 cases. We compute the decay rates and production cross sections in the main channels for spin-3/2 and spin-2 states at both electron-positron and hadron colliders, and identify the most promising novel experimental signatures for discovering such particles at the LHC. The discussion is qualitatively extended to the spin-5/2 and spin-3 cases. Higher-spin particles exhibit a rich phenomenology and have signatures that often resemble the ones of supersymmetric and extra-dimensional theories. To enable further studies of higher-spin particles at collider and beyond, we collect the relevant Feynman rules and other technical details.

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arXiv2021

Principle of Multiple Point Criticality in Multi-Scalar Dark Matter Models

The principle of multiple point criticality (PMPC), which allowed the prediction of the Higgs boson mass before its discovery, has so far been applied to radiatively generated vacua. If this principle is fundamental, following from some presently unknown underlying physics, the PMPC must apply to all vacua, including the multiple vacua of multi-scalar models dominated by tree-level terms. We first motivate this idea and then exemplify it by applying the PMPC to various realizations of singlet scalar dark matter models. We derive constraints on the dark matter properties from the requirement of degenerate vacua and show that some scalar dark matter models are ruled out by the PMPC, while in others the allowed parameters space is constrained.

hep-ph↗

arXiv2021

Confronting spin-3/2 and other new fermions with the muon g-2 measurement

The new measurement of the muon's anomalous magnetic moment released by the Muon g-2 experiment at Fermilab sets strong constraints on the properties of many new particles. Using an effective field theory approach to the interactions of higher-spin fields, we evaluate the contribution of an electrically neutral and colour singlet spin-3/2 fermion to $(g-2)_μ$ and derive the corresponding constraints on its mass and couplings. These constraints are then compared with the ones on spin-1/2 fermions, such as the vector-like leptons that are predicted by various extensions of the Standard Model, the excited leptons which appear in composite models, as well as the charginos and neutralinos of supersymmetric theories. Unlike these new spin-1/2 fermions, the spin-3/2 particles generate only small contributions to the muon anomalous magnetic moment.

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arXiv2021

Light Higgs boson from multi-phase criticality in dynamical symmetry breaking

The Coleman-Weinberg mechanism can realise different phases of dynamical symmetry breaking. In each phase a combination of scalars, corresponding to the pseudo-Goldstone boson of scale invariance, has a loop-suppressed mass. We show that additional scalars, beyond the pseudo-Goldstone bosons, can become light at critical points in the parameter space where two different phases co-exist. We present a minimal implementation of the mechanism in multi-scalar models, detailing how loop-suppressed masses and mixings can be computed. We discuss realisations of the resulting multi-phase criticality principle and its relevance to the case of the Higgs boson.

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arXiv2020

Dark matter of any spin -- an effective field theory and applications

We develop an effective field theory of a generic massive particle of any spin and, as an example, apply this to study higher-spin dark matter (DM). Our formalism does not introduce unphysical degrees of freedom, thus avoiding the potential inconsistencies that may appear in other field-theoretical descriptions of higher spin. Being a useful reformulation of the Weinberg's original idea, the proposed effective field theory allows for consistent computations of physical observables for general-spin particles, although it does not admit a Lagrangian description. As a specific realization, we explore the phenomenology of a general-spin singlet with $\mathbb{Z}_2$-symmetric Higgs portal couplings, a setup which automatically arises for high spin, and show that higher spin particles with masses above $O(10)\,\mathrm{TeV}$ can be viable thermally-produced DM candidates. Most importantly, if the general-spin DM has purely parity-odd couplings, it naturally avoids all DM direct detection bounds, in which case its mass can lie below the electroweak scale. Our formalism reproduces the existing results for low-spin DM, and allows one to develop consistent higher-spin particle physics phenomenology for high- and low-energy experiments and cosmology.

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arXiv2020

Dark Matter and the XENON1T electron recoil excess

We show that the electron recoil excess around 2 keV claimed by the Xenon collaboration can be fitted by DM or DM-like particles having a fast component with velocity of order $\sim 0.1$. Those particles cannot be part of the cold DM halo of our Galaxy, so we speculate about their possible nature and origin, such as fast moving DM sub-haloes, semi-annihilations of DM and relativistic axions produced by a nearby axion star. Feasible new physics scenarios must accommodate exotic DM dynamics and unusual DM properties.

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arXiv2020

Novel mechanism for CMB modulation in the Standard Model

We demonstrate that light spectator fields can source sizeable CMB anisotropies through modulated reheating even in the absence of direct couplings to the inflaton. The effect arises when the phase space of the inflaton decay is modulated by the spectator which generates masses for the decay products. We call the mechanism \textit{indirect modulation} and show that it can source perturbations even four orders of magnitude larger than the observed. Importantly, the indirect mechanism is present in the Standard Model extended with right-handed neutrinos. For a minimally coupled Higgs boson this leads to a novel lower bound on the quartic coupling and constrains the neutrino Yukawas below unity.

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arXiv2020

Implications of Milky Way Substructures for the Nature of Dark Matter

We study how the indirect observation of dark matter substructures in the Milky Way, using recent stellar stream studies, translates into constraints for different dark matter models. Particularly, we use the measured number of dark subhalos in the mass range $10^7-10^9\,{\rm M_{\odot}}$ to constrain modifications of the subhalo mass function compared to the cold dark matter scenario. We obtain the lower bounds $m_{\rm WDM} > 3.2\,{\rm keV}$ and $m_{\rm FDM} > 5.2\times 10^{-21}\,{\rm eV}$ on the warm dark matter and fuzzy dark matter particle mass, respectively. When dark matter is coupled to a dark radiation bath, we find that kinetic decoupling must take place at temperatures higher than $T_{\rm kd} > 0.7\,{\rm keV}$. We also discuss future prospects of stellar stream observations.

astro-ph.CO↗

arXiv2019

Small-scale structure of primordial black hole dark matter and its implications for accretion

Primordial black hole (PBH) dark matter (DM) nonlinear small-scale structure formation begins before the epoch of recombination due to large Poisson density fluctuations. Those small-scale effects still survive today, distinguishing physics of PBH DM structure formation from the one involving WIMP DM. We construct an analytic model for the small-scale PBH velocities that reproduces the velocity floor seen in numerical simulations, and investigate how these motions impact PBH accretion bounds at different redshifts. We find that the effect is small at the time of recombination, leaving the cosmic microwave background bounds on PBH abundance unchanged. However, already at $z=20$ the PBH internal motion significantly reduces their accretion due to the additional $1/v^6$ suppression, affecting the 21 cm bounds. Today the accretion bounds arising from dwarf galaxies or smaller PBH substructures are all reduced by the PBH velocity floor. We also investigate the feasibility for the PBH clusters to coherently accrete gas leading to a possible enhancement proportional to the cluster's occupation number but find this effect to be insignificant for PBH around $10 M_{\odot}$ or lighter. Those results should be reconsidered if the initial PBH distribution is not Poisson, for example, in the case of large initial PBH clustering.

astro-ph.CO↗

arXiv2019

Phase Transitions and Gravitational Wave Tests of Pseudo-Goldstone Dark Matter in the Softly Broken U(1) Scalar Singlet Model

We study phase transitions in a softly broken $U(1)$ complex singlet scalar model in which the dark matter is the pseudo-scalar part of a singlet whose direct detection coupling to matter is strongly suppressed. Our aim is to find ways to test this model with the stochastic gravitational wave background from the scalar phase transition. We find that the phase transition which induces vacuum expectation values for both the Higgs boson and the singlet - necessary to provide a realistic dark matter candidate - is always of the second order. If the stochastic gravitational wave background characteristic to a first order phase transition will be discovered by interferometers, the soft breaking of $U(1)$ cannot be the explanation to the suppressed dark matter-baryon coupling, providing a conclusive negative test for this class of singlet models.

hep-ph↗

arXiv2019

Gravitational Wave Signals of Pseudo-Goldstone Dark Matter in the $\mathbb{Z}_{3}$ Complex Singlet Model

We study pseudo-Goldstone dark matter in the $\mathbb{Z}_{3}$ complex scalar singlet model. Because the direct detection spin-independent cross section is suppressed, such dark matter is allowed in a large mass range. Unlike in the original model stabilized by a parity, due to the cubic coupling of the singlet the $\mathbb{Z}_{3}$ model can accommodate first-order phase transitions that give rise to a stochastic gravitational wave signal potentially observable in future space-based detectors.

hep-ph↗

arXiv2019

Left-Right Supersymmetry as the Origin of Flavor Physics

We propose a new framework for the observed flavor hierarchy and mixing based on left-right supersymmetry. The model contains the most minimal Higgs sector consisting only of gauge doublets which forbid the standard model Yukawa couplings. New mediator fields then connect the left- and right-chiral fermion sectors and result in effective tree level Yukawa couplings for the third generation charged fermions. The remaining fermions, including all neutrinos, acquire effective Yukawa couplings sourced by the supersymmetry breaking sector at loop level. We predict new TeV range scalars, as well as heavier fermions and vector bosons, that can be discovered at the LHC and future colliders.

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arXiv2019

Primordial black hole constraints for extended mass functions

We revisit the cosmological and astrophysical constraints on the fraction of the dark matter in primordial black holes (PBHs) with an extended mass function. We consider a variety of mass functions, all of which are described by three parameters: a characteristic mass and width and a dark matter fraction. Various observations then impose constraints on the dark matter fraction as a function of the first two parameters. We show how these constraints relate to those for a monochromatic mass function, demonstrating that they usually become more stringent in the extended case than the monochromatic one. Considering only the well-established bounds, and neglecting the ones that depend on additional astrophysical assumptions, we find that there are three mass windows, around $4\times 10^{-17}M_\odot,$ $2\times 10^{-14}M_\odot$ and $25-100M_\odot$, where PBHs can constitute all dark matter. However, if one includes all the bounds, PBHs can only constitute of order $10\%$ of the dark matter.

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