PITT PACC Workshop: Non-Standard Cosmological Epochs and Expansion Histories

5 Sept 2024, 08:30 → 7 Sept 2024, 19:05 US/Eastern

Workshop Goals & Scope:  The focus of the workshop is on possible non-standard expansion histories (involving early-matter-dominated eras, periods of kination, periods of cosmological stasis, etc.) and their observable effects in the late universe.  These might include, for example, implications for dark-matter physics (such as the production of compact mini-halos or the opening up of regions of dark-matter parameter space that might be ruled out in the standard cosmology but which might lead to distinctive annihilation or decay signals), implications for the gravitational-wave background, or implications for CMB observables. The goal is to bring together people working on different aspects of non-standard cosmological histories with the hope that our collective interactions/discussions might spark new ideas about how to probe the first few seconds of the history of the universe and help broaden our perspectives on how modifications of the cosmological expansion history might manifest themselves observationally.

Dates: September 5th -7th, 2024 (Thu. - Sat.)

Location: Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), University of Pittsburgh

Workshop Venue: Forbes Ballroom, Hilton Garden Inn Pittsburgh University Place, 3454 Forbes Ave, Pittsburgh, PA 15213 

Program Committee: Keith Dienes, Brooks Thomas, Scott Watson.

Local Organizing Committee: Brian Batell, Amit Bhoonah, Kun Cheng, Matthew Low, Zahra Tabrizi.

Administrator: Joni George

Confirmed Invited Participants:
Rouzbeh Allahverdi (New Mexico University)
Mustafa Amin (Rice University)
Kim Boddy (University of Texas at Austin)
Sten Delos (Carnegie Institute Observatories)
Adrienne Erickcek (North Carolina University)
Akshay Ghalsasi (Harvard University)
Tom Giblin (Kenyon College)
Jim Halverson (Northeastern University)
Fei Huang (Weizmann Institute of Science)
Andrew Long (Rice University)
Lauren Pearce (James Madison University)
Barmak Shams Es Haghi (University of Texas at Austin)
Jesse Shelton (University of Illinois Urbana-Champaign)
Gary Shiu (University of Wisconsin-Madison)
Kuver Sinha (University of Oklahoma)
Tristan Smith (Swarthmore College)
Keith Dienes (University of Arizona / National Science Foundation)
Brooks Thomas (Lafayette College)
Scott Watson (Syracuse University)

 

 

 

 

 

 

 

 

 

Thursday 5 September

08:30 Breakfast

1 Welcome

Speaker: Brian Thomas Batell

Welcome.pdf

2 Workshop overview

Speaker: Brooks Thomas

PITT PACC Workshop_ Block Descriptions.pdf

3 Introductions

10:30 Coffee Break

4 Block I: Connection to Observation: Overview - Presentation

Co-Discussion Leaders: Andrew Long, Kuver Sinha

This block is focused broadly on observational methods which can be used to probe the
expansion history of the universe – potentially including probes which are potentially
promising yet underappreciated – and how experimental efforts over the next decade or
so are likely to improve our understanding of that expansion history on various fronts.
However, gravitational waves, which are of course an important probe of early-universe
dynamics, will be the focus of a separate, dedicated block (Block III).

Speakers: Andrew Long (Rice University), Kuver Sinha (University of Oklahoma)

PITT PACC Workshop Slides.pdf

5 Block I: Connection to Observation: Overview - Discussion

Co-Discussion Leaders: Andrew Long, Kuver Sinha

This block is focused broadly on observational methods which can be used to probe the
expansion history of the universe – potentially including probes which are potentially
promising yet underappreciated – and how experimental efforts over the next decade or
so are likely to improve our understanding of that expansion history on various fronts.
However, gravitational waves, which are of course an important probe of early-universe
dynamics, will be the focus of a separate, dedicated block (Block III).

Speakers: Andrew Long (Rice University), Kuver Sinha (University of Oklahoma)

12:30 Lunch Break

6 Block II: Scalar Fields and Non-Standard Expansion Histories I (Top-Down Realizations and Implications for Structure Formation) - Presentation

Co-Discussion Leaders: Rouzbeh Allahverdi, Sten Delos

This is the first of two blocks focused on modifications to the cosmological expansion history which can arise in the presence of additional scalar fields (other than epochs of early matter domination, which are not unique to scalars and thus will be covered in a different block). Such modifications include, for example, early dark energy, but would also include kination epochs and other epochs wherein the universe is dominated by a fluid with a ‘stiff’ (w > 1/3) equation of state. The discussion during this block will focus on two main topics related to these themes. The first is how cosmologies involving early dark energy or cosmological components with stiff equations of state can emerge in top-down constructions involving moduli and other light scalars. The second is how the evolution of cosmological perturbations is modified in the resulting cosmologies and how such modifications can affect the matter power spectrum and the development of structure on small scales.

Speakers: Rouzbeh Allahverdi (University of New Mexico), Dr Sten Delos (Max Planck Institute for Astrophysics)

Scalar-1.pdf

7 Block II: Scalar Fields and Non-Standard Expansion Histories I (Top-Down Realizations and Implications for Structure Formation) - Discussion

Co-Discussion Leaders: Rouzbeh Allahverdi, Sten Delos

This is the first of two blocks focused on modifications to the cosmological expansion history which can arise in the presence of additional scalar fields (other than epochs of early matter domination, which are not unique to scalars and thus will be covered in a different block). Such modifications include, for example, early dark energy, but would also include kination epochs and other epochs wherein the universe is dominated by a fluid with a ‘stiff’ (w > 1/3) equation of state. The discussion during this block will focus on two main topics related to these themes. The first is how cosmologies involving early dark energy or cosmological components with stiff equations of state can emerge in top-down constructions involving moduli and other light scalars. The second is how the evolution of cosmological perturbations is modified in the resulting cosmologies and how such modifications can affect the matter power spectrum and the development of structure on small scales.

Speakers: Rouzbeh Allahverdi (University of New Mexico), Dr Sten Delos (Max Planck Institute for Astrophysics)

15:30 Coffee Break

8 Block III: Gravitational-Wave Signals in Modified Cosmologies - Presentation

Co-Discussion Leaders: Kim Boddy, Lauren Pearce

This block is focused on the gravitational-wave signatures that can arise in cosmological
scenarios involving modified expansion histories and the manner in which these signals
may be correlated with other observational signatures which might arise in such
scenarios.

Speakers: Prof. Kimberly Boddy (University of Texas at Austin), Lauren Pearce (Penn State University-New Kensington)

PITT-PACC.pdf

9 Block III: Gravitational-Wave Signals in Modified Cosmologies - Discussion

Co-Discussion Leaders: Kim Boddy, Lauren Pearce

This block is focused on the gravitational-wave signatures that can arise in cosmological
scenarios involving modified expansion histories and the manner in which these signals
may be correlated with other observational signatures which might arise in such
scenarios.

Speakers: Prof. Kimberly Boddy (University of Texas at Austin), Lauren Pearce (Penn State University-New Kensington)

Friday 6 September

08:30 Breakfast

10 Block IV: Early Matter-Dominated Eras - Presentation

Co-Discussion Leaders: Adrienne Erickcek, Jessie Shelton, Rouzbeh Allahverdi

This block is focused on early matter-dominated eras (EMDEs) and their
phenomenological/observational consequences, including implications for dark-matter
production and for structure on small scales.

Speakers: Adrienne Erickcek, Dr Jessie Shelton (University of Illinois, Urbana-Champaign)

240906-PITT-PACC.pdf

11 Block IV: Early Matter-Dominated Eras - Discussion

Co-Discussion Leaders: Adrienne Erickcek, Jessie Shelton, Rouzbeh Allahverdi

This block is focused on early matter-dominated eras (EMDEs) and their
phenomenological/observational consequences, including implications for dark-matter
production and for structure on small scales.

Speakers: Adrienne Erickcek, Dr Jessie Shelton (University of Illinois, Urbana-Champaign)

10:30 Coffee Break

12 Block V: Scalar Fields and Non-Standard Expansion Histories II (Specific Models) - Presentation

Co-Discussion Leaders: Akshay Ghalsasi, Tristan Smith

This is the second of two blocks focused on modifications to the cosmological expansion history which can arise in the presence of additional scalar fields (other than epochs of early matter domination, which are not unique to scalars and thus will be covered in a different block). Such modifications include, for example, early dark energy, but would also include kination epochs and other epochs wherein the universe is dominated by a fluid with a ‘stiff’ (w > 1/3) equation of state. The discussion during this block will focus on specific models which give rise to modifications along these lines (including axion kination and early-dark-energy scenarios) which are motivated by phenomenological and observational considerations such as the dark-matter problem, baryogenesis, and tensions between measurements made at early and late times.

Speakers: Akshay Ghalsasi (University of Pittsburgh), Tristan Smith (Swarthmore College)

Scalar-1.pdf

T_SMITH_PITTPACC-pdf.pdf

13 Block V: Scalar Fields and Non-Standard Expansion Histories I (Specific Models) - Discussion

Co-Discussion Leaders: Akshay Ghalsasi, Tristan Smith

This is the second of two blocks focused on modifications to the cosmological expansion history which can arise in the presence of additional scalar fields (other than epochs of early matter domination, which are not unique to scalars and thus will be covered in a different block). Such modifications include, for example, early dark energy, but would also include kination epochs and other epochs wherein the universe is dominated by a fluid with a ‘stiff’ (w > 1/3) equation of state. The discussion during this block will focus on specific models which give rise to modifications along these lines (including axion kination and early-dark-energy scenarios) which are motivated by phenomenological and observational considerations such as the dark-matter problem, baryogenesis, and tensions between measurements made at early and late times.

Speakers: Akshay Ghalsasi (University of Pittsburgh), Tristan Smith (Swarthmore College)

12:30 Lunch Break

14 Block VI: Connections to Fundamental Theory - Presentation

Co-Discussion Leaders: Jim Halverson, Gary Shiu

This block is focused on the connections between non-standard expansion histories and
fundamental theory. To what extent do different top-down scenarios for physics beyond
the Standard Model, including string theory, predict departures from the standard
cosmology? Conversely, were we to obtain observational evidence that indeed the
expansion history of our universe differs from that of the standard cosmology, what
would this tell us about fundamental physics at high scales?

Speakers: Prof. Gary Shiu (University of Wisconsin-Madison), Halverson Jim

Pitt PACC Discussion.pdf

Shiu-Pittsburgh.pdf

15 Block VI: Connections to Fundamental Theory - Discussion

Co-Discussion Leaders: Jim Halverson, Gary Shiu

This block is focused on the connections between non-standard expansion histories and
fundamental theory. To what extent do different top-down scenarios for physics beyond
the Standard Model, including string theory, predict departures from the standard
cosmology? Conversely, were we to obtain observational evidence that indeed the
expansion history of our universe differs from that of the standard cosmology, what
would this tell us about fundamental physics at high scales?

Speakers: Prof. Gary Shiu (University of Wisconsin-Madison), Halverson Jim

15:30 Coffee Break

16 Block VII: How Inflation Ends: Non-Standard Possibilities - Presentation

Co-Discussion Leaders: Mustafa Amin, Tom Giblin

This block is focused on the manner in which inflation ends and on the modifications to
the subsequent cosmological timeline that can take place in particular kinds of
inflationary scenarios. This includes scenarios in which reheating takes place at late
times/low temperatures, and also scenarios in which states/structures produced at the
end of inflation subsequently come to dominate the energy density of the universe or
affect the expansion history in other ways.

Speakers: Mustafa Amin, Tom Giblin (Kenyon College)

Reheating-aminandgiblin-pdf.pdf

17 Block VII: How Inflation Ends: Non-Standard Possibilities - Discussion

Co-Discussion Leaders: Mustafa Amin, Tom Giblin

This block is focused on the manner in which inflation ends and on the modifications to
the subsequent cosmological timeline that can take place in particular kinds of
inflationary scenarios. This includes scenarios in which reheating takes place at late
times/low temperatures, and also scenarios in which states/structures produced at the
end of inflation subsequently come to dominate the energy density of the universe or
affect the expansion history in other ways.

Speakers: Mustafa Amin, Tom Giblin (Kenyon College)

Saturday 7 September

08:30 Breakfast

18 Block VIII: Cosmological Stasis - Presentation

Co-Discussion Leaders: Fei Huang

This block is focused on cosmological stasis, its realizations within the context of
particular scenarios beyond the Standard Model, and its potential observational
consequences.

Speaker: Fei Huang (ITP CAS and UC Irvine)

pitt_pacc_nonstandard_cosmology.pdf

19 Block VIII: Cosmological Stasis - Discussion

Co-Discussion Leaders: Fei Huang

This block is focused on cosmological stasis, its realizations within the context of
particular scenarios beyond the Standard Model, and its potential observational
consequences.

Speaker: Fei Huang (ITP CAS and UC Irvine)

10:30 Coffee Break

20 Block IX: Primordial-Black-Hole Domination - Presentation

Co-Discussion Leaders: Barmak Shams Es Haghi

This block is focused on epochs of primordial-black-hole (PBH) domination and their
potential consequences – including, for example, possible implications for dark-matter
physics, gravitational-wave physics, and the generation of the baryon asymmetry of the
universe. An early matter-dominated eras (EMDEs) can of course arise within the
cosmological timeline when PBHs dominate. Since such eras will be the focus of a
separate, dedicated block (Block II), the focus of this block will primarily be on other
possible consequences of PBHs on the cosmological expansion history or on distinctive
potential implications of PBH-dominated eras which are not realized in other EMDEs.

Speaker: Barmak Shams Es Haghi (University of Texas at Austin)

Barmak-PBH.pdf

21 Block IX: Primordial-Black-Hole Domination - Discussion

Co-Discussion Leaders: Barmak Shams Es Haghi

This block is focused on epochs of primordial-black-hole (PBH) domination and their
potential consequences – including, for example, possible implications for dark-matter
physics, gravitational-wave physics, and the generation of the baryon asymmetry of the
universe. An early matter-dominated eras (EMDEs) can of course arise within the
cosmological timeline when PBHs dominate. Since such eras will be the focus of a
separate, dedicated block (Block II), the focus of this block will primarily be on other
possible consequences of PBHs on the cosmological expansion history or on distinctive
potential implications of PBH-dominated eras which are not realized in other EMDEs.

Speaker: Barmak Shams Es Haghi (University of Texas at Austin)

Workshop Synthesis

workshop-closing.pdf