arXiv subjects

Daniel Egana-Ugrinovic

Publications and source records attributed to Daniel Egana-Ugrinovic.

18 recordsLinked to original sources

arXiv2025

Search for continuous gravitational wave signals from luminous dark photon superradiance clouds with LVK O3 observations

Superradiance clouds of kinetically-mixed dark photons around spinning black holes can produce observable multi-messenger electromagnetic and gravitational wave signals. The cloud generates electric fields of up to a Teravolt-per-meter, which lead to a cascade production of charged particles, yielding a turbulent quasi-equilibrium plasma around the black hole, and resulting in electromagnetic fluxes ranging from supernova to pulsar-like luminosities. For stellar mass black holes, such systems resemble millisecond pulsars and are expected to emit pulsating radio waves and continuous gravitational waves (CWs) within the LIGO-Virgo-KAGRA (LVK) sensitivity band. We select 44 sources with approximately coincident frequencies or positive frequency drifts from existing pulsar catalogs as potential candidates of long-lasting superradiance clouds around old galactic black holes. For a subset of 34 sources that are well measured and have not been previously targeted, we perform the first search for CW emission in LVK data from the third observing run. We find no evidence of a CW signal and place 95% confidence level upper limits on the emitted strain amplitude. We interpret these results, together with limits from previous searches, in terms of the underlying dark photon theory by performing an analysis of the expected signals from superradiance clouds from galactic black holes. We find that, even for moderately spinning black holes, the absence of an observed CW signal disfavors a discrete set of dark photon masses between about $10^{-13}$ $\rm{eV}/c^2$ and $10^{-12}$ $\rm{eV}/c^2$ and kinetic mixing couplings in the range of $10^{-9}$-$10^{-7}$, subject to assumptions about the properties of the black hole population and the cloud's electromagnetic emission.

gr-qc↗

arXiv2023

New Physics Searches at Kaon and Hyperon Factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

hep-ph↗

arXiv2023

Dark photon superradiance: Electrodynamics and multimessenger signals

We study the electrodynamics of a kinetically mixed dark photon cloud that forms through superradiance around a spinning black hole, and design strategies to search for the resulting multimessenger signals. A dark photon superradiance cloud sources a rotating dark electromagnetic field which, through kinetic mixing, induces a rotating visible electromagnetic field. Standard model charged particles entering this field initiate a transient phase of particle production that populates a plasma inside the cloud and leads to a system which shares qualitative features with a pulsar magnetosphere. We study the electrodynamics of the dark photon cloud with resistive magnetohydrodynamics methods applicable to highly magnetized plasma, adapting techniques from simulations of pulsar magnetospheres. We identify turbulent magnetic field reconnection as the main source of dissipation and electromagnetic emission, and compute the peak luminosity from clouds around solar-mass black holes to be as large as $10^{43}$ erg/s for open dark photon parameter space. The emission is expected to have a significant X-ray component and is potentially periodic, with period set by the dark photon mass. The luminosity is comparable to the brightest X-ray sources in the Universe, allowing for searches at distances of up to hundreds of Mpc with existing telescopes. We discuss observational strategies, including targeted electromagnetic follow-ups of solar-mass black hole mergers and targeted continuous gravitational wave searches of anomalous pulsars.

astro-ph.HE↗

arXiv2022

Strange quark as a probe for new physics in the Higgs sector

This paper describes a novel algorithm for tagging jets originating from the hadronisation of strange quarks (strange-tagging) with the future International Large Detector (ILD) at the International Linear Collider (ILC). It also presents the first application of such a strange-tagger to a Higgs to strange ($h \rightarrow s\bar{s}$) analysis with the $P(e^-,e^+) = (-80\%,+30\%)$ polarisation scenario, corresponding to 900 fb$^{-1}$ of the initial proposed 2000 fb$^{-1}$ of data which will be collected by ILD during its first 10 years of data taking at $\sqrt{s} = 250$ GeV. Upper limits on the Standard Model Higgs-strange coupling strength modifier, $κ_s$, are derived at the 95% confidence level to be 7.14. The paper includes as well a preliminary study of a Ring Imaging Cherenkov (RICH) system capable of discriminating between kaons and pions at high momenta (up to 25 GeV), and thus enhancing strange-tagging performance at future Higgs factory detectors.

hep-ex↗

arXiv2022

Snowmass2021 Cosmic Frontier White Paper: Calibrations and backgrounds for dark matter direct detection

Future dark matter direct detection experiments will reach unprecedented levels of sensitivity. Achieving this sensitivity will require more precise models of signal and background rates in future detectors. Improving the precision of signal and background modeling goes hand-in-hand with novel calibration techniques that can probe rare processes and lower threshold detector response. The goal of this white paper is to outline community needs to meet the background and calibration requirements of next-generation dark matter direct detection experiments.

hep-ex↗

arXiv2022

Sources of Low-Energy Events in Low-Threshold Dark Matter and Neutrino Detectors

We discuss several low-energy backgrounds to sub-GeV dark matter searches, which arise from high-energy particles of cosmic or radioactive origin that interact with detector materials. We focus in particular on Cherenkov radiation, transition radiation, and luminescence or phonons from electron-hole pair recombination, and show that these processes are an important source of backgrounds at both current and planned detectors. We perform detailed analyses of these backgrounds at several existing and proposed experiments based on a wide variety of detection strategies and levels of shielding. We find that a large fraction of the observed single-electron events in the SENSEI 2020 run originate from Cherenkov photons generated by high-energy events in the Skipper Charge Coupled Device, and from recombination photons generated in a phosphorus-doped layer of the same instrument. In a SuperCDMS HVeV 2020 run, Cherenkov photons produced in printed-circuit-boards located near the sensor likely explain the origin of most of the events containing 2 to 6 electrons. At SuperCDMS SNOLAB, radioactive contaminants inside the Cirlex located inside or on the copper side walls of their detectors will produce many Cherenkov photons, which could dominate the low-energy backgrounds. For the EDELWEISS experiment, Cherenkov or luminescence backgrounds are subdominant to their observed event rate, but could still limit the sensitivity of their future searches. We also point out that Cherenkov radiation, transition radiation, and recombination could be a significant source of backgrounds at future experiments aiming to detect dark-matter via scintillation or phonon signals. We also discuss the implications of our results for the development of superconducting qubits and low-threshold searches for coherent neutrino scattering, and comment on design strategies that can be implemented to mitigate these backgrounds.

hep-ph↗

arXiv2022

Searching for Ultra-light Bosons and Constraining Black Hole Spin Distributions with Stellar Tidal Disruption Events

Stars that pass close to the supermassive black holes located in the center of galaxies can be violently disrupted by tidal forces, leading to flares that are observed as bright transient events in sky surveys. The rate for these events to occur depends on the black hole spins, which in turn can be affected by ultra-light bosons due to superradiance. We perform a detailed analysis of these effects and show that searches for stellar tidal disruptions have a significant potential to uncover the existence of ultra-light bosons. In particular, we find that upcoming stellar tidal disruption rate measurements by the Vera Rubin Observatory's Legacy Survey of Space and Time can be used to either discover or rule out bosons with masses ranging from $10^{-20}$ to $10^{-18}$ eV. Our analysis also indicates that these measurements may be used to constrain a variety of supermassive black hole spin distributions and determine if close-to maximal spins are preferred.

hep-ph↗

arXiv2021

The Cosmological Evolution of Self-interacting Dark Matter

We study the evolution of cosmological perturbations in dark-matter models with elastic and velocity-independent self interactions. Such interactions are imprinted in the matter-power spectrum as dark acoustic oscillations, which can be experimentally explored to determine the strength of the self scatterings. Models with self interactions have similarities to warm dark matter, as they lead to suppression of power on small scales when the dark-matter velocity dispersion is sizable. Nonetheless, both the physical origin and the extent of the suppression differ for self-interacting dark matter from conventional warm dark matter, with a dark sound horizon controlling the reduction of power in the former case, and a free-streaming length in the latter. We thoroughly analyze these differences by performing computations of the linear power spectrum using a newly developed Boltzmann code. We find that while current Lyman-$α$ data disfavor conventional warm dark matter with a mass less than 5.3 keV, when self interactions are included at their maximal value consistent with bounds from the Bullet Cluster, the limits are relaxed to 4.4 keV. Finally, we make use of our analysis to set novel bounds on light scalar singlet dark matter.

astro-ph.CO↗

arXiv2021

Multi-Higgs Production Probes Higgs Flavor

We demonstrate that multiple-Higgs production at the LHC is the most sensitive probe of first and second-generation quark flavor in the Higgs sector. In models where new scalars couple to light quarks, gigantic di-Higgs and even sizable tri-Higgs production rates can be obtained, which can be used to either discover or severely constrain such theories. As an example, we show that the most stringent bounds on enhanced interactions of the $125\,\textrm{GeV}$ Higgs to the down quark in extended Higgs sectors are obtained by looking for the extra Higgs bosons that provide for such enhancements using the di-Higgs and $Zh$ topologies. In this context, we set new limits on the 125 GeV Higgs coupling to the down quark as strong as $λ_{hd\bar{d}} \lesssim 30 λ_{hd\bar{d}}^{\textrm{SM}}$ -- a dramatic improvement over previously available bounds. Regarding second-generation quark flavor, we obtain new limits in the coupling to strange as strong as $λ_{hs\bar{s}} \lesssim 10 λ_{hs\bar{s}}^{\textrm{SM}}$. In addition, we show that the currently unexplored triple-Higgs production topology could be a potential discovery channel of a wide variety of extended Higgs sectors at the LHC, including not only models where extra Higgses couple to light quarks, but also popular theories where they have preferential couplings to the the top.

hep-ph↗

arXiv2019

Higgs bosons with large couplings to light quarks

A common lore has arisen that beyond the Standard Model (BSM) particles, which can be searched for at current and proposed experiments, should have flavorless or mostly third-generation interactions with Standard Model quarks. This theoretical bias severely limits the exploration of BSM phenomenology, and is especially constraining for extended Higgs sectors. Such limitations can be avoided in the context of Spontaneous Flavor Violation (SFV), a robust and UV complete framework that allows for significant couplings to any up or down-type quark, while suppressing flavor-changing neutral currents via flavor alignment. In this work we study the theory and phenomenology of extended SFV Higgs sectors with large couplings to any quark generation. We perform a comprehensive analysis of flavor and collider constraints of extended SFV Higgs sectors, and demonstrate that new Higgs bosons with large couplings to the light quarks may be found at the electroweak scale. In particular, we find that new Higgses as light as 100 GeV with order $\sim$ 0.1 couplings to first or second generation quarks, which are copiously produced at LHC via quark fusion, are allowed by current constraints. Furthermore, the additional SFV Higgses can mix with the SM Higgs, providing strong theory motivation for an experimental program looking for deviations in the light quark-Higgs couplings. Our work demonstrates the importance of exploring BSM physics coupled preferentially to light quarks, and the need to further develop dedicated experimental techniques for the LHC and future colliders.

hep-ph↗

arXiv2019

Light Scalars and the KOTO Anomaly

The KOTO experiment recently presented a significant excess of events in their search for the rare SM process $K_L \to π^0ν\barν$, well above both Standard Model signal and background predictions. We show that this excess may be due to weakly-coupled scalars that are produced from Kaon decays and escape KOTO undetected. We study two concrete realizations, the minimal Higgs portal and a hadrophilic scalar model, and demonstrate that they can explain the observed events while satisfying bounds from other flavor and beam-dump experiments. Hadronic beam-dump experiments provide particularly interesting constraints on these types of models, and we discuss in detail the normally underestimated uncertainties associated with them. The simplicity of the models which can explain the excess, and their possible relations with interesting UV constructions, provides strong theoretical motivation for a new physics interpretation of the KOTO data.

hep-ph↗

arXiv2018

Structure Formation and Exotic Compact Objects in a Dissipative Dark Sector

We present the complete history of structure formation in a simple dissipative dark-sector model. The model has only two particles: a dark electron, which is a subdominant component of dark matter, and a dark photon. Dark-electron perturbations grow from primordial overdensities, become non-linear, and form dense dark galaxies. Bremsstrahlung cooling leads to fragmentation of the dark-electron halos into clumps that vary in size from a few to millions of solar masses, depending on the particle model parameters. In particular, we show that asymmetric dark stars and black holes form within the Milky Way from the collapse of dark electrons. These exotic compact objects may be detected and their properties measured at new high-precision astronomical observatories, giving insight into the particle nature of the dark sector without the requirement of non-gravitational interactions with the visible sector.

hep-ph↗

arXiv2018

Aligned and Spontaneous Flavor Violation

We present a systematic spurion setup called Aligned Flavor Violation (AFV) that allows for new physics couplings to quarks that are aligned with the Standard Model (SM) Yukawas, but do not necessarily share their hierarchies nor are family universal. Additionally, we show that there is an important subset of AFV called Spontaneous Flavor Violation (SFV), which naturally arises from UV completions where the quark family number and CP groups are spontaneously broken. Flavor-changing neutral currents are strongly suppressed in SFV extensions of the SM. We study SFV from an effective field theory perspective and demonstrate that SFV new physics with significant and preferential couplings to first or second generation quarks may be close to the TeV scale.

hep-ph↗

arXiv2018

Higgs Boson Contributions to the Electron Electric Dipole Moment

The contributions of a second Higgs doublet to the electron electric dipole moment near the heavy Higgs decoupling limit are determined within an effective field theory framework. In models that satisfy the Glashow-Weinberg condition, the leading contributions in this limit at effective dimension six are shown to come from two-loop Barr-Zee diagrams that include the Standard Model-like Higgs boson. Additional diagrams that include heavy Higgs bosons are sub-leading and contribute only at effective dimension eight near the decoupling limit. This simplification implies that to leading order in this limit, contributions of a second Higgs doublet to the electron electric dipole moment can be couched entirely in terms of the ratio of Higgs doublet expectation values and a single universal phase appearing in the effective couplings of the Standard Model-like Higgs boson to fermions, without direct reference to the heavy Higgs boson masses or couplings. The recent bound from the ACME II experiment constrains the phases of the couplings of the Standard Model-like Higgs boson to up-type quarks and leptons at the part per mil level in Type I and IV two Higgs doublet models. In Type II and III models these phases are constrained at the two parts per mil or better level except in a tiny sliver of parameter space with nearly equal Higgs doublet expectation values where destructive interference among contributing diagrams happens to occur. In a more general phenomenological parameterization with individual effective phases in the couplings of the Standard Model-like Higgs boson to third generation fermions and the electron, the top quark and electron coupling phases are constrained at the part per mil level except in tiny slivers of parameter space, while the bottom quark and tau-lepton coupling phases are constrained only at the thirty percent level.

hep-ph↗

arXiv2018

Charged Fermions Below 100 GeV

How light can a fermion be if it has unit electric charge? We revisit the lore that LEP robustly excludes charged fermions lighter than about 100 GeV. We review LEP chargino searches, and find them to exclude charged fermions lighter than 90 GeV, assuming a higgsino-like cross section. However, if the charged fermion couples to a new scalar, destructive interference among production channels can lower the LEP cross section by a factor of 3. In this case, we find that charged fermions as light as 75 GeV can evade LEP bounds, while remaining consistent with constraints from the LHC. As the LHC collects more data, charged fermions in the 75-100 GeV mass range serve as a target for future monojet and disappearing track searches.

hep-ph↗

arXiv2017

The minimal fermionic model of electroweak baryogenesis

We present the minimal model of electroweak baryogenesis induced by fermions. The model consists of an extension of the Standard Model with one electroweak singlet fermion and one pair of vector like doublet fermions with renormalizable couplings to the Higgs. A strong first order phase transition is radiatively induced by the singlet-doublet fermions, while the origin of the baryon asymmetry is due to asymmetric reflection of the same set of fermions on the expanding electroweak bubble wall. The singlet-doublet fermions are stabilized at the electroweak scale by chiral symmetries and the Higgs potential is stabilized by threshold corrections coming from a multi-TeV ultraviolet completion which does not play any significant role in the phase transition. We work in terms of background symmetry invariants and perform an analytic semiclassical calculation of the baryon asymmetry, showing that the model may effectively generate the observed baryon asymmetry for percent level values of the unique invariant CP violating phase of the singlet-doublet sector. We include a detailed study of electron electric dipole moment and electroweak precision limits, and for one typical benchmark scenario we also recast existing collider constraints, showing that the model is consistent with all current experimental data. We point out that fermion induced electroweak baryogenesis has irreducible phenomenology at the $13 \, \textrm{TeV}$ LHC since the new fermions must be at the electroweak scale, have electroweak quantum numbers and couple strongly with the Higgs. The most promising searches involve topologies with multiple leptons and missing energy in the final state.

hep-ph↗

arXiv2015

Effective Theory of Higgs Sector Vacuum States

The effective field theory description for modifications of Standard Model-like Higgs boson interactions arising from tree-level mixing with heavy Higgs sector vacuum states without conserved quantum numbers is presented. An expansion in terms of effective operator dimension based on powers of the heavy mass scale rather than operator dimension is utilized to systematically organize interactions within the effective theory. Vacuum states arising from electroweak singlet extensions of the Higgs sector yield at leading order only two effective dimension-six operators. One of these uniformly dilutes all the interactions of a single physical Higgs boson as compared with Standard Model expectations, while the combination of the two operators give more general modifications of all remaining interactions with two or more physical Higgs bosons. Vacuum states arising from an additional electroweak doublet yield three types of effective dimension-six operators that modify physical Higgs boson couplings to fermion pairs, self-couplings, and introduce four-fermion interactions. However, in this case modification of physical Higgs boson interactions with massive gauge bosons arise at leading order only from three effective dimension-eight operators. If the underlying Yukawa couplings of the additional electroweak doublet satisfy the Glashow-Weinberg condition then time reversal violation at effective dimension-six depends on a single universal phase appearing only in couplings of physical Higgs bosons to fermion pairs. In all cases the couplings of any three physical states in the effective theory description must be equal to those in a unitary mixing description in order for the long distance non-analytic components of physical on-shell scattering amplitudes to agree, while in contrast couplings of four or more physical states in general differ due to short distance effects.

hep-ph↗

arXiv2015

125 GeV Higgs from Tree-Level $A$-terms

We present a new mechanism to generate large $A$-terms at tree-level in the MSSM through the use of superpotential operators. The mechanism trivially resolves the $A/m^2$ problem which plagues models with conventional, loop-induced $A$-terms. We study both MFV and non-MFV models; in the former, naturalness motivates us to construct a UV completion using Seiberg duality. Finally, we study the phenomenology of these models when they are coupled to minimal gauge mediation. We find that after imposing the Higgs mass constraint, they are largely out of reach of LHC Run I, but they will be probed at Run II. Their fine tuning is basically the minimum possible in the MSSM.

hep-ph↗