10 research outputs found

    Probing correlations of early magnetic fields using mu-distortion

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    The damping of a non-uniform magnetic field between the redshifts of about 10410^4 and 10610^6 injects energy into the photon-baryon plasma and causes the CMB to deviate from a perfect blackbody spectrum, producing a so-called μ\mu-distortion. We can calculate the correlation μT\langle\mu T\rangle of this distortion with the temperature anisotropy TT of the CMB to search for a correlation B2ζ\langle B^2\zeta\rangle between the magnetic field BB and the curvature perturbation ζ\zeta; knowing the B2ζ\langle B^2\zeta\rangle correlation would help us distinguish between different models of magnetogenesis. Since the perturbations which produce the μ\mu-distortion will be much smaller scale than the relevant density perturbations, the observation of this correlation is sensitive to the squeezed limit of B2ζ\langle B^2\zeta\rangle, which is naturally parameterized by bNLb_{\text{NL}} (a parameter defined analogously to fNLf_{\text{NL}}). We find that a PIXIE-like CMB experiments has a signal to noise S/N1.0×bNL(B~μ/10 nG)2S/N\approx 1.0 \times b_{\text{NL}} (\tilde B_\mu/10\text{ nG})^2, where B~μ\tilde B_\mu is the magnetic field's strength on μ\mu-distortion scales normalized to today's redshift; thus, a 10 nG field would be detectable with bNL=O(1)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 ζ3\langle\zeta^3\rangle induced by the magnetic field. For sufficiently small magnetic fields, the signal B2ζ\langle B^2 \zeta\rangle will dominate, but for B~μ1\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 B2ζ\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

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    We investigate the inflationary dynamics of two kinetically-coupled massless U(1)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)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

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    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

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    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 interlocução em pesquisas com música

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    Resumo: Conhecimentos se constroem com trocas simb&oacute;licas, e um tipo fundamental dessas trocas &eacute; a comunica&ccedil;&atilde;o verbal entre os sujeitos que participam de uma pesquisa. Este ensaio explora problemas e limita&ccedil;&otilde;es da interlocu&ccedil;&atilde;o para a constru&ccedil;&atilde;o epist&ecirc;mica, considerando tamb&eacute;m os fatores dial&oacute;gicos que trazem ganhos &agrave; pesquisa com pr&aacute;ticas de m&uacute;sica, 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 investiga&ccedil;&atilde;o com m&uacute;sica, propondo debates e continuidade de experi&ecirc;ncias pautadas pela aten&ccedil;&atilde;o &agrave;s rela&ccedil;&otilde;es criadas entre os participantes durante e ap&oacute;s o trabalho de campo. Palavras-chave: Interlocu&ccedil;&atilde;o. Trabalho de campo. Pr&aacute;ticas de m&uacute;sica. &Eacute;tica e epistemologia Considering dialogue in music research &nbsp; 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&nbsp; 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.&nbsp; &nbsp; Keywords:&nbsp; Dialogue. Fieldwork. Musical practices. Ethics and epistemology &nbsp
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