Cambridge High Energy Workshop 2021 - Axion Physics

27 Jul 2021, 09:00 → 30 Jul 2021, 16:00 America/New_York

Zoom / Gather.town

General Information:

The particle physics groups at Harvard and MIT are organizing the first Cambridge High Energy Workshop. This year the focus of this topical BSM workshop is on recent developments in Axion physics, including recent experimental results, new proposals, model building ideas, and formal developments.

Format:

The workshop will consist of short talks (20 + 10 minutes) by invited speakers, followed by extensive discussion time over gather.town.

Zoom and Gather.town addresses:

The links for the zoom room and the discussion area over gather.town will be emailed to the registered participants.

Organizers:

Pouya Asadi, Katie Fraser,  Samuel Homiller, Qianshu Lu, Rashmish Mishra, Aditya Parikh, John Stout 

Advising Faculty: 

 Howard Georgi, Lisa Randall, Matthew Reece, Tracy Slatyer, Iain Stewart, Washington Taylor, Jesse Thaler

Invited Speakers:

• Mohammad Anber 
• T. Daniel Brennan 
• Manuel Buen-Abad 
• Francesca Chadha-Day
• Raymond Co
• Jeff Dror
• Yohei Ema
• Hajime Fukuda
• Marios Galanis
• Christina Gao
• Isabel Garcia Garcia
• Rachel Houtz
• Andrew Long
• Azadeh Maleknejad
• Gustavo Marques-Tavares
• Ryutaro Matsudo
• Sam McDermott
• Chanda Prescod-Weinstein
• Wolfram Ratzinger
• Masaki Yamada
• Norikazu Yamada
• Chelsea Bartram (on behalf of ADMX)
• Kaliroe Pappas (on behalf of ABRACADABRA)
• Saptarshi Chaudhuri (on behalf of DMRadio)

 

Tuesday, 27 July

09:50 → 10:00 Welcome

chew-2021-welcome.pdf

10:00 → 11:30 Session 1

10:00 Venturing a glimpse of the dark matter halo with ADMX

I will present recent results from and future plans of the Axion Dark Matter eXperiment (ADMX). Recent results include a first pass axion search of the 800-1020 MHz frequency range at half DFSZ sensitivity for 100% axion dark matter density, the demonstration of a traveling wave parametric amplifier (TWPA) for higher-frequency wide-band operation, and a multi-mode candidate identification technique. Near term plans include the coverage of 800-1020 MHz with full sensitivity to DFSZ coupled axion dark matter, followed by a multicavity upgrade to reach up to 2 GHz. Longer term plans include a significant experiment re-work to reach DFSZ axions at 2 GHz and above, as well as a variety of new ideas that would tackle existing limitations of haloscope searches.

Speaker: Chelsea Bartram (University of Washington)

Axion_BSM_Workshop.key

Axion_BSM_Workshop.pdf

Day1_AM1_Chelsea_Bartram.mp4

10:30 ABRACADABRA-10cm: searching for long-wavelength axions

Originally proposed as a solution to the strong CP problem, the axion is also well motivated as a candidate for dark matter. In the less-explored axion mass range below 1 ueV axions behave as long-wavelength dark matter, the search for which requires novel approaches and techniques. With ABRACADABRA-10cm we demonstrate the ability to search for GUT-scale axions in the range of 0.3 to 8 neV using a superconducting toroidal magnet, quantum electronics, and a broadband lumped-element circuit. In this talk, I will be discussing ABRACADABRRA-10cm as a whole and the result from our most recent run, where we were able to place world-leading limits on axion coupling in the neV mass range.

Speaker: Kaliroe Pappas (MIT laboratory for nuclear science)

Day1_AM2_Kaliroe_Pappas.mp4

HarvardWorkshop.pdf

11:00 Dark Matter Radio

I present Dark Matter Radio (DMRadio), a multi-faceted program to probe axion dark matter below 1 ueV using an electromagnetic lumped-element resonator. I describe the detection concept and design principles and discuss present experimental status. DMRadio-50L, under construction, will probe axion-like particles in the 20 peV-20 neV mass range. It will serve as a testbed for sensors evading the Standard Quantum Limit on amplification. A scaled-up detector DMRadio-m3, under design study, has projected sensitivity to the QCD axion between 20 neV-800 neV. I present an R&D roadmap towards DMRadio-GUT, a challenging, long-term experiment to probe GUT-scale QCD axions near 1 neV.

Speaker: Saptarshi Chaudhuri (Princeton University)

Dark Matter Radio_CambridgeAxions2021.pdf

Day1_AM3_Sapatarshi_Chaudhuri.mp4

11:30 → 14:00 Discussion 1

14:00 → 15:30 Session 2

14:00 Microphysics from Astrophysics

In this talk, I will discuss a range of approaches to better understand ultralight and light scalar dark matter candidates, including axion-like particles. I will discuss results from PySiUltraLight, a modification of the PyUltraLight code that includes self-interaction terms to model the dynamical evolution of axion fields. I will discuss work that shows that the self-interaction should not be ignored and that the sign of the interaction makes a significant difference in the evolution of the system, both for QCD axions and fuzzy dark matter. I will also describe results showing that in the high-occupancy regime of scalar dark matter, the Boltzmann collision integral does not describe either gravitational or self-interactions. Finally, I will mention some ongoing efforts to use neutron star observations to constrain the presence of dark matter.

Speaker: Chanda Prescod-Weinstein (University of New Hampshire)

Day1_PM1_Chanda_Prescod-Weinstein.mp4

14:30 Constraints on Axions from Cosmic Distance Measurements

Axion couplings to photons could induce photon-axion conversion in the presence of magnetic fields in the Universe. This conversion could impact various cosmic distance measurements, such as luminosity distances to type Ia supernovae and angular distances to galaxy clusters, in different ways. In this talk we consider different combinations of the most up-to-date distance measurements to constrain the axion-photon coupling. Employing the conservative cell magnetic field model for the magnetic fields in the intergalactic medium (IGM) and ignoring the conversion in the intracluster medium (ICM), we find the upper bounds on axion-photon couplings to be around $5\times 10^{−12}~(\mathrm{nG}/B)~\sqrt{\mathrm{Mpc}/s}~\mathrm{GeV}^{−1}$ for axion masses below $10^{−13}~\mathrm{eV}$, where B is the strength of the IGM magnetic field, and s is the comoving size of the magnetic domains. When including the conversion in the ICM, the upper bound is lowered and could reach $5\times 10^{−13}~\mathrm{GeV}^{−1}$ for masses below $5 \times 10^{−12}~\mathrm{eV}$. While this stronger bound depends on the ICM modeling, it is independent of the strength of the IGM magnetic field.

Speaker: Manuel A. Buen-Abad (Brown University)

AxP - Su21 - Cosmo Axions -- M. Buen-Abad.pdf

Day1_PM2_Manuel_Buen-Abad.mp4

15:00 The Cosmic Axion Background

Existing searches for cosmic axions relics have relied heavily on the axion being non-relativistic and making up dark matter. However, light axions can be copiously produced in the early Universe and remain relativistic today, thereby constituting a Cosmic axion Background (CaB). As prototypical examples of axion sources, we consider thermal production, dark-matter decay, parametric resonance, and topological defect decay. Each of these has a characteristic frequency spectrum that can be searched for in axion direct detection experiments. We focus on the axion-photon coupling and study the sensitivity of current and future versions of ADMX, HAYSTAC, DMRadio, and ABRACADABRA to a CaB, finding that the data collected in search of dark matter can be repurposed to detect axion energy densities well below limits set by measurements of the energy budget of the Universe. In this way, direct detection of relativistic relics offers a powerful new opportunity to learn about the early Universe and, potentially, discover the axion.

Speaker: Jeff Dror (UC Santa Cruz)

Day1_PM3_Jeff_Dror.mp4

ParallelTalk_AxionWorkshop.pdf

15:30 → 16:30 Discussion 2

Wednesday, 28 July

10:00 → 11:30 Session 3

10:00 Axion Quasiparticles for Axion Dark Matter Detection

Axion quasiparticles may exist in certain condensed matter systems. I will discuss the physics of axion quasiparticles, and how they may be used to detect axion dark matter via three-way mixing between the photon, axion and axion quasiparticle. I will introduce the proposed TOORAD experiment for TOpolOgical Resonant Axion Detection.

Speaker: Dr Francesca Chadha-Day (Durham University)

Day2_AM1_Francesca_Chadha-Day.mp4

TOORAD talk.pdf

10:30 Axion Searches with two Superconducting Radio Frequency Cavities

Axion (and axion-like-particle), a pseudo-scalar well-motivated in the beyond-the-Standard-Model physics, has a unique two photon vertex, which allows terrestrial experiments to directly look for them from the Sun or as a component of dark matter. Laboratory searches, with both the source and the detection of axion under control, so-called Light-shining-through-walls (LSW), are complementary probes to those direct searches above. We propose a LSW axion search strategy using superconducting radio-frequency (SRF) cavities in the GHz range. SRF cavities have exceptionally high quality factor, which both boost the number of photons stored in the emitter cavity, and enhance the signal power in the receiver cavity.

Speaker: Christina Gao (Fermilab)

Day2_AM2_Christina_Gao.mp4

11:00 Searching for axions with X-rays from magnetic white dwarf stars

Axions couple extremely weakly to regular matter, making them challenging to probe in the laboratory. However, axions should be produced in the hot and dense environments of compact stars, providing these stars with an additional cooling channel that leads to well-known constraints on the axion’s couplings to matter. These constraints are indirect, and although compact stars are predicted to “glow” in axions, this radiation is invisible to us. In this talk I will discuss how the axion radiation is converted into X-ray emission in the strong magnetic field that surround many compact stars, thereby providing a new strategy for probing axions through X-ray observations of white dwarfs and neutron stars.

Speaker: Andrew Long (Rice University)

ALong_CHEW2021.pdf

Day2_AM3_Andrew_Long.mp4

11:30 → 14:00 Discussion 3

14:00 → 15:30 Session 4

14:00 Audible Axions

Conventional approaches to probing axions and axion-like particles (ALPs)typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. We show that such invisible axions, which are viable candidates for dark matter, can produce a stochastic gravitational wave background in the early universe and are therefore audible. This signal is generated in models where the invisible axion couples to a dark gauge boson that experiences a tachyonic instability when the axion begins to oscillate. Quantum fluctuations in the gauge boson get exponentially amplified and source chiral gravitational waves. We present lattice calculations of the resulting GW signal and highlight its detectability. Furthermore we give an outlook on possible model implementations.

Speaker: Wolfram Ratzinger (University of Mainz)

Cambridge2021.pdf

Day2_PM1_Wolfram_Ratzinger.mp4

14:30 New Physics and the Black Hole Mass Gap

The LIGO/Virgo collaboration is making astonishing discoveries at a fantastic pace, including a heavy binary black hole merger with component masses in the “black hole mass gap,” which cannot be explained by standard stellar structure theory. In this talk, I will discuss how new light particles that couple to the Standard Model can act as an additional source of energy loss in the cores of population-III stars, dramatically altering their evolution and potentially explaining mass-gap objects. I will also demonstrate how new population catalogs can help distinguish different scenarios for the origin of these objects.

Speaker: Sam McDermott (Fermilab)

Day2_PM2_Sam_McDermott.mp4

mcdermott-bhmg-CHEW21.pdf

15:00 Dynamical Axions and Gravitational Waves

In this talk I discuss the gravitational wave signals of dynamical axion models. In particular, I focus on models which solve the strong CP problem and include the confinement of a QCD-like gauge group at the TeV scale. Interestingly, the amplitude of the gravitational wave spectrum depends on the mass of the dynamical axion. The resulting spectra may be observed at future mid-range gravitational wave experiments such as AION/MAGIS, DECIGO, and BBO. Moreover, the TeV states can be searched for at colliders, providing a unique connection between axion physics, gravitational waves and collider searches.

Speaker: Rachel Houtz (Durham IPPP)

CHEW 2021 - Houtz.pdf

Day2_PM3_Rachel_Houtz.mp4

15:30 → 16:30 Discussion 4

Thursday, 29 July

09:00 → 10:30 Session 5

09:00 Peeking into the theta vacuum of 4d SU(2) Yang-Mills theory

We propose a subvolume method to study the $\theta$ dependence of the free energy density of the four-dimensional SU($N$) Yang-Mills theory on the lattice. As an attempt, the method is first applied to SU(2) Yang-Mills theory at $T=1.2\,T_c$ to understand the systematics of the method. We then proceed to the calculation of the vacuum energy density and obtain the $\theta$ dependence, at least, to $\theta\sim\pi$. The numerical results combined with the theoretical requirements provide the evidence for the spontaneous CP violation at $\theta = \pi$, which is in accordance with the large $N$ prediction and in contrast to the CP$^1$ model in two dimensions.

Speaker: Norikazu Yamada (KEK)

2021.07.29-CHEW2021-yamada.pdf

Day3_AM1_Norikazu_Yamada.mp4

09:30 Fermions as "axion" strings in a monopole background

In the monopole background, multi-fermion operators exhibit condensation. The phases of the operators are "axions" in the sense that they are topologically coupled to the electromagnetic field. We propose that an ``excited'' closed axion string is the fermion itself. We use this picture to solve a long-standing puzzle in the scattering process of a monopole and a massless fermion. It has been known that when a charged fermion scatters off a monopole, the fermion in the s-wave component must flip its chirality, i.e., fermion number violation must happen. This fact has led to a puzzle; if there are two or more flavors of massless fermions, any superposition of the fermion states cannot be the final state of the s-wave scattering as it is forbidden by conservation of the electric and flavor charges. The unitary evolution of the state vector, on the other hand, requires some interpretation of the final states. We show that the final state should be an axion string that is interpreted as a new particle excitation of the theory.

Speaker: Ryutaro Matsudo (KEK Theory Center)

Day3_AM2_Ryutaro_Matsudo.mp4

10:00 Axions, Higher-Groups, and Emergent Symmetry

Axion models are phenomenologically relevant QFTs that exhibit higher group global symmetries. Higher groups describe the case when different types of higher form symmetries combine together in a non-trivial structure. In this talk, we will discuss how the emergence of these higher groups can be used to infer non-trivial constraints on the RG flows of theories that flow to axion-Yang-Mills in the IR.

Speaker: T Daniel Brennan (University of Chicago)

AxionHigherGroup-Talk.pdf

Day3_AM3_Daniel_Brennan.mp4

10:30 → 13:00 Discussion 5

13:00 → 14:30 Session 6

13:00 Generalized anomalies and axion physics

Axions are conspicuous in particle physics; their role in physics beyond the Standard Model and cosmology cannot be overestimated. Despite the fact that they have been around for more than 40 years, recent formal developments have brought in new lessons on the interplay between axions and strong dynamics. In this talk, I discuss a new class of generalized 't Hooft anomalies that was recently identified, and then use the anomalies to argue that quarks are deconfined on axion domain walls. This phenomenon implies that a nontrivial intertwining between different scales happens on the walls; the simple effective cosine potential breaks down as the axion makes a large excursion in the field space. I also discuss the implication of this finding for models of natural inflation.

Speaker: Mohamed Anber (Lewis & Clark College)

Anomalies-axions_BSM.pdf

Day3_PM1_Mohamed_Anber.mp4

13:30 Axion assisted Schwinger effect

Particle production in strong electromagnetic fields, the Schwinger effect, is a recurring theme in solid state physics, heavy ion collisions, early universe cosmology and formal quantum field theory. In this talk, after reviewing the standard Schwinger effect, we show that the pair production rate of charged fermions in a strong electric field is enhanced in the presence of time dependent classical axion-like background field, which we call axion assisted Schwinger effect. While the standard Schwinger production rate is proportional to $\exp(−\pi(m^2+p^2_T)/E)$, with $m$ and $p_T$ denoting the fermion mass and its momentum transverse to the electric field $E$, the axion assisted Schwinger effect can be enhanced at large momenta to $\exp(−\pi m^2/E)$. We interpret the origin of this enhancement as a coupling between the fermion spin and its momentum, induced by the axion velocity.

Speaker: Yohei Ema (DESY)

Day3_PM2_Yohei_Ema.mp4

YEma_CHEW2021.pdf

14:00 Axion dynamics and topics in Chern-Simons theory

The axion has an exact 2pi shift symmetry. The symmetry is a redundancy of the system and the axion can be regarded as a gauge Boson of the redundancy. From this point of view, the axion interaction is the so-called Chern-Simons term, behind which rich dynamics are known to be.
I will review the axion as the gauge Boson and introduce our work on dynamics of the axion in terms of the Chern-Simons theory, which had been less known before.

Speaker: Hajime Fukuda

chew2021.pptx

Day3_PM3_Hajime_Fukuda.mp4

14:30 → 15:30 Discussion 6

Friday, 30 July

09:00 → 10:30 Session 7

09:00 Cosmic Birefringence Triggered by Dark Matter Domination

Cosmic birefringence is predicted if an axion-like particle (ALP) moves after the recombination epoch. We show that this naturally happens if the ALP is coupled to the dark matter density because it then acquires a large effective mass after the matter-radiation equality. We give a simple model to realize this scenario, where dark matter is made of hidden monopoles, which give the ALP such a large effective mass through the Witten effect. The mechanism works if the ALP decay constant is of order the GUT-scale without a fine-tuning of the initial misalignment angle.

Speaker: Masaki Yamada (Tohoku University)

Day4_AM1_Masaki_Yamada.mp4

MYamada.pdf

09:30 Axion strings as cosmic accelerators

We study new signatures associated with electromagnetic properties of axion strings. We focus
on charge deposition onto axion strings from electromagnetic fields and
the subsequent novel neutralizing
mechanisms due to bound state formation. While early universe
signatures appear unlikely, there are a plethora of late time
signatures. Axion strings passing through galaxies obtain an enormous
charge density, which is quickly neutralized by a dense plasma of bound state
Standard Model particles forming a one dimensional ``atom''. The
charged wave packets on the string, as well as the dense plasma
outside, travel at nearly the speed of light along the string. These
packets of high energy plasma collide with a center of mass energy of
up to $10^{9}$ GeV. These collisions can have luminosities up to seven
orders of magnitude larger than the solar luminosity, and last for
thousands of years, making them visible at radio telescopes even when
they occur at cosmological distances.

Speaker: Gustavo Marques-Tavares (University of Maryland)

Day4_AM2_Gustavo_Marques-Tavares.mp4

10:00 Superradiance of self-interacting scalar fields

Black hole superradiance is a powerful probe of light, weakly-coupled hidden sector particles. Particles with a Compton wavelength comparable to the black hole’s radius lead to an instability, extracting mass and angular momentum from the black hole. Many ultralight candidates, such as axions, generically have self-interactions that can influence the evolution of the superradiant instability.  Self-interactions lead to energy exchange between bound levels and particle emission to infinity; for large self-couplings, superradiant growth is saturated at a quasi-equilibrium configuration of reduced level occupation numbers. In this talk, I will review the basic aspects of black hole superradiance and give a qualitative picture of how it changes when quartic self-interactions are present. Finally, I will discuss possible signatures, which include coherent, monochromatic gravitational and axion waves that can be probed in current or future experiments.

Speaker: Marios Galanis (Stanford University)

BH_SR_self-interactions_CHEW2021.pdf

Day4_AM3_Marios_Galanis.mp4

10:30 → 13:00 Discussion 7

13:00 → 14:30 Session 8

13:00 Is Our Universe the Remnant of Chiral Anomaly in Axion Inflation?

Modern cosmology has been remarkably successful in describing the universe from a second after the Big Bang until today. However, its physics before that time is still much less certain. It profoundly involves particle theory beyond the Standard Model to explain long-standing puzzles: the origin of the observed matter asymmetry, and massive neutrinos, as well as the particle physics of dark matter and cosmic inflation. In this talk, I will explain that a new framework based on embedding axion-inflation in left-right symmetric gauge extensions of the SM can possibly solve and relate these seemingly unrelated mysteries of modern cosmology. The baryon asymmetry and dark matter today may be remnants of a pure quantum effect (chiral anomaly) in inflation which is the source of CP violation in inflation. As a smoking gun, this setup has robust observable signatures for the GW background to be probed by future CMB missions and laser interferometer detectors.

Speaker: Azadeh Maleknejad (CERN)

CHEW-2.pdf

Day4_PM1_Azadeh_Maleknejad.mp4

13:30 New Roles of the Axion in Dark Matter, Baryogenesis, and Gravitational Waves

We propose a paradigm where the QCD axion’s unexplored cosmological evolution, a rotation in the field space, gives rise to dark matter, the baryon asymmetry, and/or gravitational waves. The rotation is initiated by explicit Peccei-Quinn (PQ) symmetry breaking effective in the early Universe. The abundance of axion dark matter is determined by the rotational speed via what we call kinetic misalignment. With the aid of the Standard Model sphaleron processes (and potentially the neutrino Majorana mass term), the PQ charge associated with the rotation is transferred to the baryon asymmetry. We name these baryogenesis mechanisms by axiogenesis (and lepto-axiogenesis). The paradigm predicts 1) an axion coupling stronger than the conventional ones and 2) an electroweak phase transition earlier than predicted by the Standard Model (or instead the presence of the neutrino Majorana mass). If the axion couples to a dark photon, this new axion dynamics can also generate gravitational wave signals across the observable frequencies.

Speaker: Raymond Co (University of Minnesota)

Day4_PM2_Raymond_Co.mp4

New Roles of Axions.pdf

14:00 P Not PQ

Parity solutions to the strong CP problem are a compelling alternative to approaches based on Peccei-Quinn symmetry, particularly given the expected violation of global symmetries in a theory of quantum gravity. The most natural of these solutions break parity at a low scale, giving rise to a host of experimentally accessible signals. We assess the status of the simplest parity-based solution in light of LHC data and flavor constraints, highlighting the prospects for near-future tests at colliders, tabletop experiments, and gravitational wave observatories. The origin of parity breaking and associated gravitational effects play crucial roles, providing new avenues for discovery through EDMs and gravity waves. These experimental opportunities underline the promise of generalized parity, rather than Peccei-Quinn symmetry, as a robust and testable solution to the strong CP problem.

Speaker: Isabel Garcia Garcia (KITP)

Day4_PM3_Isabel_Garcia_Garcia.mp4

14:30 → 15:30 Discussion 8