LR w/ Fan, Katz, Reece Agrawal, Cyr-Racine, Scholtz, Brownsberger, Kramer, Rowan, Xu
What’s post-modern? As with particle physics, easy times are probably at an end Need to look at subtle effects Basically (as with SM) Λ CDM SM essentially works But we don’t know if it’s whole story Several things I’m working on (which to present?) Black hole mergers and what they can tell you Hubble expansion: most interesting discrepancy! ** Dark matter: how to find what it is from astronomical measurements
Nature of Dark Matter?? Compact objects or particle If a particle, what is it Mass, interactions? If not a WIMP, can we observe its consequences? Astronomical MEASUREMENTS AND STRUCTURE Our program: Propose models Systematic exploration of simple possibilities Analytic and numerical predictions Make measurements Emphasize could be ONLY way we learn about dark matter’s identity
Self-Interacting Dark Matter Dark matter that interacts with itself Not necessarily with ordinary matter Has testable consequences Might even address issues with CDM How to pursue this theoretically? And determine consequences?
Particular Focus: Darkly-Charged Dark Matter Simple idea: Assume dark matter charged under its own “electromagnetism”: “dark light” Dark matter charge, U(1) Could be light and heavy (like proton and electron) Could be just heavy dark matter candidate (and antiparticle) Thought to be very constrained Even though NOT a WIMP Turns out can be weak scale mass with EM-type coupling Or if a fraction of dark matter can be even less constrained
Second Focus: PIDM/DDDM Partially Interacting/Double Disk Dark matter with its own force Rather than assume all dark matter Assume it’s only a fraction Maybe like baryons? Nonminimal assumption But one with significant consequences Will be tested Leads to rethinking of implications of almost all dark matter, astronomical, cosmological measurements Since we don’t know what dark matter is Should keep an open mind Especially in light of abundance of astronomical data
Simple(st?) Model: DCDM • WIMP miracle Dark “proton” aka Charged WIMP • Asymmetirc g D A µ D X γ µ X freezeout • Neff • Matter power spectrum +Dark electron • Asymmetric recombination g D A µ D C γ µ C • CMB • Cores +Kinetic Mixing • Halo shapes • SIDM - ε /2 F D µ ν F µ ν • Dark Disk • Point Sources • Direct Detction
I: Darkly-Charged Dark Matter Model Dark matter charged under its own “electromagnetism”
Why Dark Charges Disfavored ”Constraints” Ellipticity of halos Bullet Cluster type constraints Survival of dwarf galaxies in halos (lack of evaporation) Seemed to significantly impinge on parameter space
Why Dark Charges Disfavored ”Constraints” Ellipticity of halos Bullet Cluster type constraints Survival of dwarf galaxies in halos (lack of evaporation) Seemed to significantly impinge on parameter space
Previous Constraints too Stonrg Galaxy ellipticity was strongest constraint Ellipticity tricky to calculate It’s a function of radius And only one galaxy measured anyway Dwarf galaxy survival calculation different when massless mediator: strong internal interactions in dwarf Bullet cluster relies on initial distributions
Ellipticity as function of radius
Darkly-Charged Dark Matter Clearly viable!! Constraints on mass considerably weaker than stated Not yet reliable Simulations can help Exciting possibility that dark matter has its own world of interactions And that conceivably we can detect them Weak mass particles with even EM-type strength
New Regime of Interactions
Partially Interacting Dark Matter Nonminimal assumption: why would we care? Implications of a subdominant component Can be relevant for signals if it is denser Can be relevant for structure –like baryons Baryons matter because formed in a dense disk Perhaps same for componen t of dark matter Dark disk inside galactic plane Or Point sources after fragmentation Potentially significant consequences Leads to rethinking of implications of almost all dark matter, astronomical, cosmological measurements Detectable! Velocity distributions in or near galactic plane constrain fraction to be comparable or less to that of baryons Further constraints from CMB But because it is in disk and dense signals can be rich
Simple DDDM Model New Ingredient: Light C Could be U(1) or a nonabelian group U(1) D , α D Two matter fields: a heavy fermion X and a light fermion C For “coolant” as we will see q X =1, q C =-1 (In principle, X and C could also be scalars) (in principle nonconfining nonabelian group) This in addition to dark matter particle that makes up the halo
Summary of model A heavy component Brehm and inverse Compton For disk to form, require light component With these conditions, expect a dark disk Even narrower than the gaseous disk
Traditional Methods Smaller direct detection, small velocity Possibly other noncanonical possibilities Indirect detection Possible if mediation between visible, invisible sectors Good thing there is distinctive shape to signal if present Best search: directly with GAIA data Use density, velocity measurements to deduce gravitational potential
Also: Satellites of Andromeda w/Scholtz Galaxy About half the satellites are approximately in a (big plane) 14kpc thick, 400 kpc wide Hard to explain Proposed explanation: tidal force of two merging galaxies Fine except of excessive dark matter content Tidal force would usually pull out only baryonic matter from disk Not true if dark disk Pulls out dark matter Slower velocity—more likely to be bound So even subdominant component in disk can be dominant in dwarfs
Also potentially Point sources Evidence for GeV excess Seems to come from point sources Argued that pulsars are the source Could also be point sources from COMPACT dark matter objects Possible when dissipative! Dark photon leads to cooling Instabilities leads to compact objects Annihilations through Z’ lead to visible signals Due to mixing with photon Would appear as point sources
New Work: Dwarfs: predicted prolate “observed” oblate Linda Xu We consider the morphologies of dwarf spheroidals (dsphs) in and around the Local Group (LG). Ellipticities and associated 3-D shapes, and whether they might be prolate or oblate. Compare CDM- sourced simulations to observations
How to measure? Dsphs: common, little gas, eqm stars determined from grav potential Simulations: prolate halos so we expect the stellar distributions of dsphs sourced from CDM haloes should be likewise prolate. But how to deduce 3D structure when we make 2d observations? Expect the surface brightness of a prolate galaxy is anti- correlated with its projected ellipticity, while the opposite is true of oblate galaxies. Use this to deduce 3d structure
Results Discrepancy between the morphologies of LG dwarf galaxies with mass-to-light ratio > 100M/L and those of the FIRE dwarf galaxies
Statistically significant deviation from expectations Linda Xu • New feature to look for when checking Λ CDM predictions
General Lesson Role for particle physics approach in astronomy “constraint” on dark disk came from fitting standard components Turns out errors on standard components not properly accounted for Reddening important near midplane Has to be done self-consistently Here different components influence each other through gravity Big messy data sets Targeting a model helps
Conclusions Very interesting new possibility for dark matter That one might expect to see in observations ard to know whether or not it’s likely How much should dark matter resemble SM But not be part of it But presumably would affect structure Just like baryons do Research area Rich arena: lots of questions to answer
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