10 research outputs found

### Probing correlations of early magnetic fields using mu-distortion

The damping of a non-uniform magnetic field between the redshifts of about
$10^4$ and $10^6$ injects energy into the photon-baryon plasma and causes the
CMB to deviate from a perfect blackbody spectrum, producing a so-called
$\mu$-distortion. We can calculate the correlation $\langle\mu T\rangle$ of
this distortion with the temperature anisotropy $T$ of the CMB to search for a
correlation $\langle B^2\zeta\rangle$ between the magnetic field $B$ and the
curvature perturbation $\zeta$; knowing the $\langle B^2\zeta\rangle$
correlation would help us distinguish between different models of
magnetogenesis. Since the perturbations which produce the $\mu$-distortion will
be much smaller scale than the relevant density perturbations, the observation
of this correlation is sensitive to the squeezed limit of $\langle
B^2\zeta\rangle$, which is naturally parameterized by $b_{\text{NL}}$ (a
parameter defined analogously to $f_{\text{NL}}$). We find that a PIXIE-like
CMB experiments has a signal to noise $S/N\approx 1.0 \times b_{\text{NL}}
(\tilde B_\mu/10\text{ nG})^2$, where $\tilde B_\mu$ is the magnetic field's
strength on $\mu$-distortion scales normalized to today's redshift; thus, a 10
nG field would be detectable with $b_{\text{NL}}=\mathcal{O}(1)$. However, if
the field is of inflationary origin, we generically expect it to be accompanied
by a curvature bispectrum $\langle\zeta^3\rangle$ induced by the magnetic
field. For sufficiently small magnetic fields, the signal $\langle B^2
\zeta\rangle$ will dominate, but for $\tilde B_\mu\gtrsim 1$ nG, one would have
to consider the specifics of the inflationary magnetogenesis model.
We also discuss the potential post-magnetogenesis sources of a $\langle
B^2\zeta\rangle$ correlation and explain why there will be no contribution from
the evolution of the magnetic field in response to the curvature perturbation.Comment: 23 pages, 1 figure. v2: Noted that a competing effect could
potentially be smaller than originally stated. Fixed references. Matches JCAP
versio

### Inflationary dynamics of kinetically-coupled gauge fields

We investigate the inflationary dynamics of two kinetically-coupled massless
$U(1)$ gauge fields with time-varying kinetic-term coefficients. Ensuring that
the system does not have strongly coupled regimes shrinks the parameter space.
Also, we further restrict ourselves to systems that can be quantized using the
standard creation, annihilation operator algebra. This second constraint limits
us to scenarios where the system can be diagonalized into the sum of two
decoupled, massless, vector fields with a varying kinetic-term coefficient.
Such a system might be interesting for magnetogenesis because of how the
strong coupling problem generalizes. We explore this idea by assuming that one
of the gauge fields is the Standard Model $U(1)$ field and that the other dark
gauge field has no particles charged under its gauge group. We consider whether
it would be possible to transfer a magnetic field from the dark sector,
generated perhaps before the coupling was turned on, to the visible sector. We
also investigate whether the simple existence of the mixing provides more
opportunities to generate magnetic fields. We find that neither possibility
works efficiently, consistent with the well-known difficulties in inflationary
magnetogenesis.Comment: 17 pages, 0 figures. Matches JCAP versio

### Calculating the local-type fNL for slow-roll inflation with a non-vacuum initial state

Single-field slow-roll inflation with a non-vacuum initial state has an
enhanced bispectrum in the local limit. We numerically calculate the local-type
fNL signal in the CMB that would be measured for such models (including the
full transfer function and 2D projection). The nature of the result depends on
several parameters, including the occupation number N_k, the phase angle
\theta_k between the Bogoliubov parameters, and the slow-roll parameter
\epsilon. In the most conservative case, where one takes \theta_k \approx
\eta_0 k (justified by physical reasons discussed within) and \epsilon\lesssim
0.01, we find that 0 < fNL < 1.52 (\epsilon/0.01), which is likely too small to
be detected in the CMB. However, if one is willing to allow a constant value
for the phase angle \theta_k and N_k=O(1), fNL can be much larger and/or
negative (depending on the choice of \theta_k), e.g. fNL \approx 28
(\epsilon/0.01) or -6.4 (\epsilon/0.01); depending on \epsilon, these scenarios
could be detected by Planck or a future satellite. While we show that these
results are not actually a violation of the single-field consistency relation,
they do produce a value for fNL that is considerably larger than that usually
predicted from single-field inflation.Comment: 8 pages, 1 figure. v2: Version accepted for publication in PRD. Added
greatly expanded discussion of the phase angle \theta_k; this allows the
possibility of enhanced fNL, as mentioned in abstract. More explicit
comparisons with earlier wor

### Scale-dependent bias of galaxies and mu-type distortion of the cosmic microwave background spectrum from single-field inflation with a modified initial state

We investigate the phenomenological consequences of a modification of the
initial state of a single inflationary field. While single-field inflation with
the standard Bunch-Davies initial vacuum state does not generally produce a
measurable three-point function (bispectrum) in the squeezed configuration,
allowing for a non-standard initial state produces an exception. Here, we
calculate the signature of an initial state modification in single-field
slow-roll inflation in both the scale-dependent bias of the large-scale
structure (LSS) and mu-type distortion in the black-body spectrum of the cosmic
microwave background (CMB). We parametrize the initial state modifications and
identify certain choices of parameters as natural, though we also note some
fine-tuned choices that can yield a larger bispectrum. In both cases, we
observe a distinctive k^-3 signature in LSS (as opposed to k^-2 for the
local-form). As a non-zero bispectrum in the squeezed configuration correlates
a long-wavelength mode with two short-wavelength modes, it induces a
correlation between the CMB temperature anisotropy on large scales with the
temperature-anisotropy-squared on very small scales; this correlation persists
as the small-scale anisotropy-squared is processed into mu-type distortions.
While the local-form mu-distortion turns out to be too small to detect in the
near future, a modified initial vacuum state enhances the signal by a large
factor owing to an extra factor of k_1/k. For example, a proposed
absolutely-calibrated experiment, PIXIE, is expected to detect this correlation
with a signal-to-noise ratio greater than 10, for an occupation number of about
0.5 in the observable modes. Relatively calibrated experiments such as Planck
and LiteBIRD should also be able to measure this effect, provided that the
relative calibration between different frequencies meets the required
precision. (Abridged)Comment: 14 pages, 6 figures. Matches version in PRD. Improved explanation in
Sec. IV; added references and corrected typo

### Refletindo sobre a interlocuÃ§Ã£o em pesquisas com mÃºsica

Resumo: Conhecimentos se constroem com trocas simbólicas, e um tipo fundamental dessas trocas é a comunicação verbal entre os sujeitos que participam de uma pesquisa. Este ensaio explora problemas e limitações da interlocução para a construção epistêmica, considerando também os fatores dialógicos que trazem ganhos à pesquisa com práticas de música, em termos de legitimidade e interesse dos participantes. Discute modos de produzir conhecimentos e apresentar resultados, e comenta pesquisas recentes em contexto brasileiro. Dirige-se a pesquisadores em linhas diversas de investigação com música, propondo debates e continuidade de experiências pautadas pela atenção às relações criadas entre os participantes durante e após o trabalho de campo. Palavras-chave: Interlocução. Trabalho de campo. Práticas de música. Ética e epistemologia Considering dialogue in music research Abstract: Knowledge is produced by means of symbolic exchanges, including, as a basic form, the verbal communication between the persons who take part in a research. This essay explores problems and limitations of interlocution in relation to epistemic construction, considering, on the other hand, the dialogical factors that may lead a research of musical practices to various gains in terms of its legitimacy and interest of the participants. It discusses the modes of producing knowledge and presenting results, and commentates recent researches in Brazil. The essay is directed to researchers in various pathways of music investigation, proposing further discussions and the continuity of experiences oriented by the attention to relations between participants during and after fieldwork. Keywords: Dialogue. Fieldwork. Musical practices. Ethics and epistemology  

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### Understanding the signatures of single-field inflation in cosmological probes

textI will investigate the primordial squeezed limit bispectrum as produced by inflation in single-field models. Previous results have argued that generically, single-field inflation produces a negligible bispectrum. However, more careful evaluation yields a more ambiguous result. I will discuss an alternate method for calculating the squeezed limit bispectrum for a general single-field inflation model. I will also explore slow-roll inflation with a non-standard initial state, where we find an enhanced squeezed-limit. I will discuss the detectability of such models in various cosmological observables such as the Cosmic Microwave Background (CMB), Large Scale Structure, and mu-distortion of the CMB.Physic