<p>We suggest a dynamical mechanism which explains why, in the supersymmetric Ishibashi-Kawai-Kitazawa-Tsuchiya matrix model, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>O</mi><mo stretchy="false">(</mo><mn>9</mn><mo stretchy="false">)</mo></math> symmetry of the Lagrangian is spontaneously broken to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>O</mi><mo stretchy="false">(</mo><mn>3</mn><mo stretchy="false">)</mo><mo>×</mo><mi>S</mi><mi>O</mi><mo stretchy="false">(</mo><mn>6</mn><mo stretchy="false">)</mo></math>, allowing only three large classical spatial dimensions to emerge. The argument relies on the identification of D-strings as stable excitations of the matrices about the cosmological background and the absence of forces between parallel D-string excitations. A spatial dimension can only become large if the D-strings winding in that direction can annihilate. In the absence of forces, this requires the string-world sheets to intersect, a process which is highly suppressed if more than three dimensions of space are large. Implications for a recently proposed matrix cosmology scenario are discussed.</p>

Canada

Robert Brandenberger

Julia Pasiecznik

Origin of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>O</mi><mo stretchy="false">(</mo><mn>9</mn><mo stretchy="false">)</mo><mo stretchy="false">→</mo><mi>S</mi><mi>O</mi><mo stretchy="false">(</mo><mn>3</mn><mo stretchy="false">)</mo><mo>×</mo><mi>S</mi><mi>O</mi><mo stretchy="false">(</mo><mn>6</mn><mo stretchy="false">)</mo></math> symmetry breaking in the type IIB matrix model

We study a two-matrix toy model with a BFSS-like interaction term using the collective field formalism. The main technical simplification is obtained by gauge-fixing first, and integrating out the off-diagonal elements, before changing to the collective field variable. We show that the resulting (2 + 1)-dimensional collective field action has novel features with respect to non-locality, and that we need to add a mass term to get a time-local potential. As is expected, one recovers the single matrix quantum mechanical collective field Hamiltonian in the proper limit.

not found

Suddhasattwa Brahma

Keshav Dasgupta

Yue Lei

Collective field theory of gauged multi-matrix models: integrating out off-diagonal strings

We study the effects of superfluid dark matter on the structure of a cosmic string wake, considering both the effects of regular and quantum pressure terms. We consider the total fluid to consist of a combination of baryons and dark matter. Hence, we are also able to study the effects of superfluid dark matter on the distribution of baryons inside the wake. We focus on parameter values for the superfluid dark matter which allow a MONDian explanation of galaxy rotation curves.

Aline Favero

A superfluid dark matter cosmic string wake

We study the interplay of the trans-Planckian censorship conjecture (TCC) and the swampland distance conjecture (SDC) in the context of multifield dark energy in a curved field space. In this scenario, the phase of accelerated expansion is realized as nongeodesic motion in a highly curved field space, reminiscent of models developed in the context of inflation. The model features a stable attractor solution with near constant equation of state <math><mi>w</mi><mo>≃</mo><mo>−</mo><mn>1</mn></math>, and predicts that the current era of accelerated expansion is eternal. The latter implies an eventual conflict with the TCC, which holds that the duration of any epoch of cosmic acceleration is bounded by the requirement that the large-scale observable universe is blind to Planck-scale early universe physics. This tension can be resolved by an interplay with the distance conjecture: for suitable parameter values, the apparent violation of the TCC occurs well after the fields have traversed a Planckian distance. The SDC then predicts a breakdown of the effective field theory before the TCC can be violated. We derive the constraints on the model arising from the <math><mrow><mi>SDC</mi><mo>+</mo><mi>TCC</mi></mrow></math> and the de Sitter conjecture. We demonstrate that the model can be consistent with both swampland conjectures and observational data from Planck 2018 and the Dark Energy Spectroscopic Instrument.

Guillaume Payeur

Evan McDonough

Swampland conjectures constraints on dark energy from a highly curved field space

Embedded walls are domain wall solutions which are unstable in the vacuum but stabilized in a plasma of the early Universe. We show how embedded walls in which the electroweak symmetry is restored can lead to an efficient scenario of electroweak baryogenesis. We construct an extension of the Standard Model of particle physics in which embedded walls exist and are stabilized in an electromagnetic plasma.

Germany

Tobias Schröder

Embedded domain walls and electroweak baryogenesis

We study the implications of the stringy spacetime uncertainty relation (STUR) for inflationary cosmology. By demanding that no fluctuation modes that exit the Hubble radius are affected by the nonlocality resulting from the STUR, we find an upper bound on the number of e-foldings of inflation. The bound is a factor of 2 weaker than what results from the trans-Planckian censorship criterion (TCC). By demanding that the inflationary phase is simultaneously consistent with STUR and sufficiently long for inflation to provide a causal explanation of structure on the scale of the current Hubble radius, we find an upper bound on the energy scale of inflation. The bound is less restrictive than what follows from the TCC, but it remains in conflict with canonical single-field inflation models.

Taiwan

Pei-Ming Ho

Hikaru Kawai

Wei-Hsiang Shao

Stringy spacetime uncertainty principle and a modified trans-Planckian censorship criterion

We consider the back-reaction of cosmological fluctuations on the local expansion rate averaged over a space-like hypersurface of constant value of a clock field. We show that in the infrared limit, the fluctuations lead to a decrease in the average expansion rate, measured at a fixed value of the clock field, compared to what would be obtained in a homogeneous universe. We work in the context of Einstein gravity coupled to perfect fluid matter.

Vincent Comeau

Switzerland

Back-reaction of long-wavelength cosmological fluctuations as measured by a clock field

We apply the Gaussian expansion method to the BFSS matrix model in the high temperature limit. When the (Euclidean) BFSS action is expanded about a Gaussian ansatz, it is shown that the SO(9) symmetry is spontaneously broken, analogous to what happens in the IKKT model. The analysis of the free energy, using the set of gap equations which determines the width of the Gaussian terms, is sufficient to show that this symmetry breaking happens only when the fermionic terms are included and is absent in the bosonic case.

United Kingdom

Samuel Laliberte

Spontaneous symmetry breaking in the BFSS model: analytical results using the Gaussian expansion method

Recently, Pei-Ming Ho and Hikaru Kawai [1] have argued that treating particles as wave packets can lead to a shutdown of Hawking radiation after a scrambling time in the case of Schwarzschild black holes. This shutdown arises from viewing quantum field theory near the black hole horizon as an effective field theory, and imposing an appropriate UV cutoff. We show that this effect is also present in the static patch of de Sitter space, leading to a shutdown of Gibbons-Hawking radiation at late times. Assuming this effect is due to the breakdown of effective field theory, we obtain a bound t ≲ H  −1 ln(H  −1 M  P ) on the time scale of validity of effective field theory in de Sitter space, which matches with the predictions of the Trans-Planckian Censorship Conjecture.

Mattéo Blamart

TCC bounds on the static patch of de Sitter space

We argue that, in the same way that in a black hole space-time VECROs will form in order to cancel the gravitational effects of a collapsing mass shell and prevent the formation of a singularity, in a contracting universe a gas of VECROs will form to hold up the contraction, prevent a Big Crunch singularity, and lead to a nonsingular cosmological bounce.