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Neal Weiner

Publications and source records attributed to Neal Weiner.

At least 37 records · Page 2Linked to original sources
arXiv2020

The Power of Halometry

Astrometric weak gravitational lensing is a powerful probe of the distribution of matter on sub-Galactic scales, which harbor important information about the fundamental nature of dark matter. We propose a novel method that utilizes angular power spectra to search for the correlated pattern of apparent motions of celestial objects induced from time-dependent lensing by a population of Galactic subhalos. Application of this method to upcoming astrometric datasets will allow for the direct measurement of the properties of Galactic substructure, with implications for the underlying particle physics. We show that, with near-future astrometric observations, it may be possible to statistically detect populations of cold dark matter subhalos, compact objects, as well as density fluctuations sourced by scalar field dark matter. Currently-unconstrained parameter space will already be accessible using upcoming data from the ongoing Gaia mission.

astro-ph.CO↗
arXiv2020

First Results on Dark Matter Substructure from Astrometric Weak Lensing

Low-mass structures of dark matter (DM) are expected to be entirely devoid of light-emitting regions and baryons. Precisely because of this lack of baryonic feedback, small-scale substructures of the Milky Way are a relatively pristine testing ground for discovering aspects of DM microphysics and primordial fluctuations on subgalactic scales. In this work, we report results from the first search for Galactic DM subhalos with time-domain astrometric weak gravitational lensing. The analysis is based on a matched-filter template of local lensing corrections to the proper motion of stars in the Magellanic Clouds. We describe a data analysis pipeline detailing sample selection, background subtraction, and handling outliers and other systematics. For tentative candidate lenses, we identify a signature based on an anomalous parallax template that can unequivocally confirm the presence of a DM lens, opening up prospects for robust discovery potential with full time-series data. We present our constraints on substructure fraction $f_l \lesssim 5$ at 90% CL (and $f_l \lesssim 2$ at 50% CL) for compact lenses with radii $r_l < 1\,\mathrm{pc}$, with best sensitivity reached for lens masses $M_l$ around $10^7$-$10^8\,M_\odot$. Parametric improvements are expected with future astrometric data sets; by end of mission, $Gaia$ could reach $f_l \lesssim 10^{-3}$ for these massive point-like objects, and be sensitive to lighter and/or more extended subhalos for $\mathcal{O}(1)$ substructure fractions.

astro-ph.CO↗
arXiv2019

A Portalino to the Twin Sector

Extensions of the Standard Model are often highly constrained by cosmology. The presence of new states can dramatically alter observed properties of the universe by the presence of additional matter or entropy. In particular, attempts too solve the hierarchy problem through naturalness invariably predict new particles near the weak scale which come into thermal equilibrium. Without a means to deposit this energy into the SM, these models are often excluded. Scenarios of "neutral naturalness" especially, such as the Twin Higgs frequently suffer from this. However, the Portalino, a singlet fermion that marries gauge neutral fermion operators, can naturally help provide a portal for entropy to return to the SM and to lift fermionic degrees of freedom in the Twin Sector. Together with spontaneous breaking of the $Z_2$ ${\rm SM \leftrightarrow {\rm Twin}}$ symmetry, there are new opportunities to confront the cosmological challenges of these models. Here, we attempt to develop such ideas. We shall show how one can lift many of the light fields by breaking $\ztwo$ with a $U(1)_Y$ scalar and its Twin partner. The introduction of Portalinos can lift the remaining degrees of freedom. We shall find that such models are highly constrained by precision SM measurements, motivating moderate extensions beyond this. We will discuss two, one with additional weak matter and another with additional colored matter. The weak model will involve simple two Higgs doublet models on top of $\ztwo$ breaking. The strong model will involve the presence of new leptoquarks and diquarks. We will discuss the implications for neutrino masses from radiative corrections and possible colored signals even within these models of neutral naturalness, some of which might appear at the LHC or future colliders.

hep-ph↗
arXiv2018

A Portalino to the Dark Sector

"Portal" models that connect the Standard Model to a Dark Sector allow for a wide variety of scenarios beyond the simplest WIMP models. Kinetic mixing of gauge fields in particular has allowed a broad range of new ideas. However, the models that evade CMB constraints are often non-generic, with new mass scales and operators to split states and suppress indirect detection signals. Models with a "portalino", a neutral fermion that marries a linear combination of a standard model neutrino and dark sector fermion and carries a conserved quantum number, can be simpler. This is especially interesting for interacting dark sectors; then the unmarried linear combination which we identify as the standard model neutrino inherits these interactions too, and provides a new, effective interaction between the dark sector and the standard model. These interactions can be simple $Z'$ type interactions or lepton-flavor changing. Dark matter freezes out into neutrinos, thereby evading CMB constraints, and conventional direct detection signals are largely absent. The model offers different signals, however. The "portalino" mechanism itself predicts small corrections to the standard model neutrino couplings as well as the possibility of discovering the portalino particle in collider experiments. Possible cosmological and astroparticle signatures include monochromatic neutrino signals from annihilation, spectral features in high energy CR neutrinos as well as conventional signals of additional light species and dark matter interactions.

hep-ph↗
arXiv2018

Halometry from Astrometry

Halometry---mapping out the spectrum, location, and kinematics of nonluminous structures inside the Galactic halo---can be realized via variable weak gravitational lensing of the apparent motions of stars and other luminous background sources. Modern astrometric surveys provide unprecedented positional precision along with a leap in the number of cataloged objects. Astrometry thus offers a new and sensitive probe of collapsed dark matter structures over a wide mass range, from one millionth to several million solar masses. It opens up a window into the spectrum of primordial curvature fluctuations with comoving wavenumbers between $5~\text{Mpc}^{-1}$ and $10^5~\text{Mpc}^{-1}$, scales hitherto poorly constrained. We outline detection strategies based on three classes of observables---multi-blips, templates, and correlations---that take advantage of correlated effects in the motion of many background light sources that are produced through time-domain gravitational lensing. While existing techniques based on single-source observables such as outliers and mono-blips are best suited for point-like lens targets, our methods offer parametric improvements for extended lens targets such as dark matter subhalos. Multi-blip lensing events may also unveil the existence, location, and mass of planets in the outer reaches of the Solar System, where they would likely have escaped detection by direct imaging.

astro-ph.CO↗
arXiv2017

Light Signals from a Lighter Higgs

With the Higgs search program already quite mature, there is the exciting possibility of discovering a new particle with rates near that of the SM Higgs. We consider models with a signal in $γγ$ below the SM Higgs mass, taking the recent $2.9\, σ$ (local) CMS excess at 95 GeV as a target. We discuss singlet models with additional vectorlike matter, but argue that a Type-I two Higgs doublet model provides a more economical scenario. In such a setup, going into regions of moderate-to-strong fermiophobia, the enhanced $γγ$ branching ratio allows signals from $VH$+VBF production to yield $σ\times BR_{γγ} $ comparable to total SM rates. Light $H$ production can be dominated via rare top decays $t \rightarrow b H^+ \rightarrow b W^{*} H$, which provides an alternate explanation of the excess. We consider this in the context of other Higgs anomalies, namely the LEP Higgs excess near the same mass, and excesses in $t\bar{t}h$ searches at Tevatron and LHC. We find that with $140\, \mathrm{GeV} < m_{H^+} < 160\, \mathrm{GeV}$, $\tan β\sim 5$ and a coupling to gauge bosons of $\sin^2 δ\sim 0.1$, such a scenario can produce all the excesses simultanously, where $tth$ arise from contamination from the rare top decays, as previously proposed. An implication of the Type-I scenario is that any $γγ$ excess should be associated with additional elements that could reduce background, including $b$-jets, forward jets or signs of vector boson production.

hep-ph↗
arXiv2017

Charged Higgs Signals in $t\,\overline{t}\,H$ Searches

New scalars from an extended Higgs sector could have weak scale masses and still have escaped detection. In a Type I Two Higgs Doublet Model, for instance, even the charged Higgs can be lighter than the top quark. Because electroweak production of these scalars is modest, the greatest opportunity for their detection might come from rare top decays. For mass hierarchies of the type $m_t>m_{H^\pm}>m_{A^0,\,H^0}$, the natural signal can arise from top quark pair production, followed by the decay chain $t \rightarrow b\,H^+$, $H^+ \rightarrow W^{+(*)} ϕ^0$, $ϕ^0\rightarrow b\overline{b},\,τ^+τ^-$, where $ϕ^0=A^0,\,H^0$. These final states largely overlap with those of the Standard Model $t\,\bar{t}\,H^0_{_\text{SM}}$ process, and therefore can potentially contaminate $t\,\bar{t}\,H^0_{_\text{SM}}$ searches. We demonstrate that existing $t\,\bar{t}\,H^0_{_\text{SM}}$ analyses can already probe light extended Higgs sectors, and we derive new constraints from their results. Furthermore, we note that existing excesses in $t\,\bar{t}\,H^0_{_\text{SM}}$ searches can be naturally explained by the contamination of rare top decays to new light Higgses. We discuss how to distinguish this signal from the Standard Model process.

hep-ph↗
arXiv2016

Simplified Models for Dark Matter Searches at the LHC

This document outlines a set of simplified models for dark matter and its interactions with Standard Model particles. It is intended to summarize the main characteristics that these simplified models have when applied to dark matter searches at the LHC, and to provide a number of useful expressions for reference. The list of models includes both s-channel and t-channel scenarios. For s-channel, spin-0 and spin-1 mediation is discussed, and also realizations where the Higgs particle provides a portal between the dark and visible sectors. The guiding principles underpinning the proposed simplified models are spelled out, and some suggestions for implementation are presented.

hep-ph↗
arXiv2015

Goldstone Gauginos

Models of supersymmetry with Dirac gauginos provide an attractive scenario for physics beyond the standard model. The "supersoft" radiative corrections and suppressed SUSY production at colliders provide for more natural theories and an understanding of why no new states have been seen. Unfortunately, these models are handicapped by a tachyon which is naturally present in existing models of Dirac gauginos. We argue that this tachyon is absent, with the phenomenological successes of the model preserved, if the right handed gaugino is a (pseudo-)Goldstone field of a spontaneously broken anomalous flavor symmetry.

hep-ph↗
arXiv2015

Signals of a Light Dark Force in the Galactic Center

Recent evidence for an excess of gamma rays in the GeV energy range about the Galactic Center have refocused attention on models of dark matter in the low mass regime ($m_χ\lesssim m_Z/2$). Because this is an experimentally well-trod energy range, it can be a challenge to develop simple models that explain this excess, consistent with other experimental constraints. We reconsider models where the dark matter couples to dark photon, which has a weak kinetic mixing to the Standard Model photon, or scalars with a weak mixing with the Higgs boson. We focus on the light ($\lesssim 1.5 GeV$) dark mediator mass regime. Annihilations into the dark mediators can produce observable gamma rays through decays to $π^0$, through radiative processes when decaying to charged particles ($e^+e^-, μ^+μ^-,...$), and subsequent interactions of high energy $e^+e^-$ with gas and light. However, these models have no signals of $\bar p$ production, which is kinematically forbidden. We find that in these models, the shape of resulting gamma-ray spectrum can provide a good fit to the excess at Galactic Center. We discuss further constraints from AMS-02, and find regions of compatibility.

hep-ph↗
arXiv2015

Models of Goldstone Gauginos

Models with Dirac gauginos provide appealing scenarios for physics beyond the standard model. They have smaller radiative corrections to the Higgs mass, a suppression of certain SUSY production processes, and ameliorated flavor constraints. Unfortunately, they also generally have tachyons, the solutions to which typically spoil these positive features. The recently proposed "Goldstone Gaugino" mechanism provides a simple solution that eliminates these tachyonic states. We provide details on this mechanism and explore models for its origin. In particular, we find SUSY QCD models that realize this idea simply, and discuss scenarios for unification.

hep-ph↗
arXiv2014

Looking for new charged states at the LHC: Signatures of Magnetic and Rayleigh Dark Matter

Magnetic and Rayleigh dark matter are models describing weak interactions of dark matter with electromagnetism through non-renormalizable operators of dimensions 5 and 7, respectively. Such operators motivate the existence of heavier states that couple to dark matter and are also charged under the electroweak interactions. The recent hints of a gamma-ray line in the Fermi data suggest that these states may be light enough to be produced at the LHC. We categorize such states according to their charges and decay modes, and we examine the corresponding LHC phenomenology. We emphasize unconstrained models that can be discovered in targeted searches at the upgraded LHC run, while also enumerating models excluded by current data. Generally, models with SU(2)-singlet states or models where the charged states decay predominantly to tau leptons and/or gauge bosons are still viable. We propose searches to constrain such models and, in particular, find superior performance over existing proposals for multi-tau analyses. Finally, we note several scenarios, especially those dominated by tau final states, that cannot be probed even with 300/fb at LHC14, motivating the further refinement of tau lepton searches to improve sensitivity to such final states.

hep-ph↗
arXiv2014

An X-Ray Line from eXciting Dark Matter

The eXciting Dark Matter (XDM) model was proposed as a mechanism to efficiently convert the kinetic energy (in sufficiently hot environments) of dark matter into e+e- pairs. The standard scenario invokes a doublet of nearly degenerate DM states, and a dark force to mediate a large upscattering cross section between the two. For heavy ($\sim TeV$) DM, the kinetic energy of WIMPs in large (galaxy-sized or larger) halos is capable of producing low-energy positrons. For lighter dark matter, this is kinematically impossible, and the unique observable signature becomes an X-ray line, arising from $χχ\rightarrow χ^* χ^*$, followed by $χ^* \rightarrow χγ$. This variant of XDM is distinctive from other DM X-ray scenarios in that it tends to be most present in more massive, hotter environments, such as clusters, rather than nearby dwarfs, and has different dependencies from decaying models. We find that it is capable of explaining the recently reported X-ray line at 3.56 keV. For very long lifetimes of the excited state, primordial decays can explain the signal without the presence of upscattering. Thermal models freeze-out as in the normal XDM setup, via annihilations to the light boson $ϕ$. For suitable masses the annihilation $χχ\rightarrow ϕϕ$ followed by $ϕ\rightarrow SM$ can explain the reported gamma-ray signature from the galactic center. Direct detection is discussed, including the possibility of explaining DAMA via the "Luminous" dark matter approach. Quite generally, the proximity of the 3.56 keV line to the energy scale of DAMA motivates a reexamination of electromagnetic explanations. Other signals, including lepton jets and the modification of cores of dwarf galaxies are also considered.

hep-ph↗
arXiv2013

Dark Matter in Light of LUX

The landscape of dark matter direct detection has been profoundly altered by the slew of recent experiments. While some have claimed signals consistent with dark matter, others have seen few, if any, events consistent with dark matter. The results of the putative detections are often incompatible with each other in the context of naive spin-independent scattering, as well as with the null results. In particular, in light of the conflicts between the DM interpretation of the three events recently reported by the CDMS-Si experiment and the first results of the LUX experiment, there is a strong need to revisit the assumptions that go into the DM interpretations of both signals and limits. We attempt to reexamine a number of particle physics, astrophysics and experimental uncertainties. Specifically, we examine exothermic scattering, isospin-dependent couplings, modified halo models through astrophysics independent techniques, and variations in the assumptions about the scintillation light in liquid Xenon. We find that only a highly tuned isospin-dependent scenario remains as a viable explanation of the claimed detections, unless the scintillation properties of LXe are dramatically different from the assumptions used by the LUX experiment.

hep-ph↗
arXiv2013

Hiding Missing Energy in Missing Energy

Searches for supersymmetry (SUSY) often rely on a combination of hard physics objects (jets, leptons) along with large missing transverse energy to separate New Physics from Standard Model hard processes. We consider a class of ``double-invisible'' SUSY scenarios: where squarks, stops and sbottoms have a three-body decay into two (rather than one) invisible final-state particles. This occurs naturally when the LSP carries an additional conserved quantum number under which other superpartners are not charged. In these topologies, the available energy is diluted into invisible particles, reducing the observed missing energy and visible energy. This can lead to sizable changes in the sensitivity of existing searches, dramatically changing the qualitative constraints on superpartners. In particular, for m_LSP>160 GeV, we find no robust constraints from the LHC at any squark mass for any generation, while for lighter LSPs we find significant reductions in constraints. If confirmed by a full reanalysis from the collaborations, such scenarios allow for the possibility of significantly more natural SUSY models. While not realized in the MSSM, such phenomenology occurs naturally in models with mixed sneutrinos, Dirac gauginos and NMSSM-like models.

hep-ph↗
arXiv2013

Dark matter detection in two easy steps

Multi-component dark matter particles may have a more intricate direct detection signal than simple elastic scattering on nuclei. In a broad class of well-motivated models the inelastic excitation of dark matter particles is followed by de-excitation via $γ$-decay. In experiments with fine energy resolution, such as many $0ν2β$ decay experiments, this motivates a highly model-independent search for the sidereal daily modulation of an unexpected $γ$ line. Such a signal arises from two-step WIMP interaction: the WIMP is first excited in the lead shielding and subsequently decays back to the ground state via the emission of a monochromatic $γ$ within the detector volume. We explore this idea in detail by considering the model of magnetic inelastic WIMPs, and take a sequence of CUORE-type detectors as an example. We find that under reasonable assumptions about detector performance it is possible to efficiently explore mass splittings of up to few hundreds of keV for a WIMP of weak-scale mass and transitional magnetic moments. The modulation can be cheaply and easily enhanced by the presence of additional asymmetric lead shielding. We devise a toy simulation to show that a specially designed asymmetric shielding may result in up to $30\%$ diurnal modulations of the two-step WIMP signal, leading to additional strong gains in sensitivity.

hep-ph↗
arXiv2013

How Dark Are Majorana WIMPs? Signals from MiDM and Rayleigh Dark Matter

The effective interactions of dark matter with photons are fairly restricted. Yet both direct detection as well as monochromatic gamma ray signatures depend sensitively on the presence of such interactions. For a Dirac fermion, electromagnetic dipoles are possible, but are very constrained. For Majorana fermions, no such terms are allowed. We consider signals of an effective theory with a Majorana dark matter particle and its couplings to photons. In the presence of a nearby excited state, there is the possibility of a magnetic dipole transition (Magnetic inelastic Dark Matter or MiDM), which yields both direct and indirect detection signals, and, intriguingly, yields essentially the same size over a wide range of dipole strengths. Absent an excited state, the leading interaction of WIMPs is similar to the Rayleigh scattering of low energy photons from neutral atoms, which may be captured by an effective operator of dimension 7 of the form $\barχχF_{μν}F^{μν}$. While it can be thought of as a phase of the Magnetic inelastic Dark Matter scenario where the excited state is much heavier than the ground state, it can arise from other theories as well. We study the resulting phenomenology of this scenario: gamma ray lines from the annihilation of WIMPs; nuclear recoils in direct detection; and direct production of the WIMP pair in high-energy colliders. Considering recent evidence in particular for a 130 GeV line from the galactic center, we discuss the detection prospects at upcoming experiments.

hep-ph↗