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1. • CommentRowNumber1.
   • CommentAuthorUrs
   • CommentTimeApr 25th 2011
   • PermaLink
   Author: Urs
   Format: MarkdownItexadded to [[orientifold]] some basic notions on orientifold circle $n$-bundles.

   added to orientifold some basic notions on orientifold circle $n$-bundles.

2. • CommentRowNumber2.
   • CommentAuthorUrs
   • CommentTimeApr 25th 2011
   • PermaLink
   Author: Urs
   Format: MarkdownItexhave added more details on the Jandl-gerbe model and its relation to the DFM-model.

   have added more details on the Jandl-gerbe model and its relation to the DFM-model.

3. • CommentRowNumber3.
   • CommentAuthorUrs
   • CommentTimeApr 4th 2014
   • PermaLink
   Author: Urs
   Format: MarkdownItexI have rewritten the first paragraphs of _[[orientifold]]_ and removed some of the technical discussion that I had there. Will write an improved version these days.

   I have rewritten the first paragraphs of orientifold and removed some of the technical discussion that I had there. Will write an improved version these days.

4. • CommentRowNumber4.
   • CommentAuthorUrs
   • CommentTimeOct 2nd 2018
   • PermaLink
   Author: Urs
   Format: MarkdownItexHave expanded the list of references. In particular I added pointer to [Hanany-Kol 00](https://ncatlab.org/nlab/show/orientifold#HananyKol00), which, as I just discovered, gives on its p 11 a lightning sketch of the classification of those $p$-brane involutions in Prop. 4.7 of our "[Real ADE-equivariant (co-)homotopy](https://arxiv.org/abs/1805.05987)" <a href="https://ncatlab.org/nlab/revision/diff/orientifold/42">diff</a>, <a href="https://ncatlab.org/nlab/revision/orientifold/42">v42</a>, <a href="https://ncatlab.org/nlab/show/orientifold">current</a>

   Have expanded the list of references. In particular I added pointer to Hanany-Kol 00, which, as I just discovered, gives on its p 11 a lightning sketch of the classification of those $p$-brane involutions in Prop. 4.7 of our “Real ADE-equivariant (co-)homotopy”

   diff, v42, current

5. • CommentRowNumber5.
   • CommentAuthorUrs
   • CommentTimeMay 12th 2019
   • (edited May 12th 2019)
   • PermaLink
   Author: Urs
   Format: MarkdownItexadded pointer to this reference: * Philip C. Argyres, [[Ron Maimon]], Sophie Pelland, _The M theory lift of two O6 planes and four D6 branes_, JHEP 0205 (2002) 008 ([arXiv:hep-th/0204127](https://arxiv.org/abs/hep-th/0204127)) (didn't realize before that [[Ron Maimon]] has such a publication -- or maybe I am misidentifying the author?) Also slightly re-arranged the references, putting all the M-theory lifts into their own subsection <a href="https://ncatlab.org/nlab/revision/diff/orientifold/55">diff</a>, <a href="https://ncatlab.org/nlab/revision/orientifold/55">v55</a>, <a href="https://ncatlab.org/nlab/show/orientifold">current</a>

   added pointer to this reference:

   • Philip C. Argyres, Ron Maimon, Sophie Pelland, The M theory lift of two O6 planes and four D6 branes, JHEP 0205 (2002) 008 (arXiv:hep-th/0204127)

   (didn’t realize before that Ron Maimon has such a publication – or maybe I am misidentifying the author?)

   Also slightly re-arranged the references, putting all the M-theory lifts into their own subsection

   diff, v55, current

6. • CommentRowNumber6.
   • CommentAuthorUrs
   • CommentTimeMay 12th 2019
   • PermaLink
   Author: Urs
   Format: MarkdownItex(whether it's him or not, it's fun getting distracted from googling his online writings; [here](https://www.quora.com/Is-Ron-Maimon-proud-that-he-attended-Harvard/answer/Ron-Maimon?share=1) he explains that the orgies at Harvard are "not done well", in contrast to those at Cornell, and why)

   (whether it’s him or not, it’s fun getting distracted from googling his online writings; here he explains that the orgies at Harvard are “not done well”, in contrast to those at Cornell, and why)

7. • CommentRowNumber7.
   • CommentAuthorUrs
   • CommentTimeMay 16th 2019
   • PermaLink
   Author: Urs
   Format: MarkdownItexadded pointer to today's * [[Pedram Hekmati]], [[Michael Murray]], [[Richard Szabo]], [[Raymond Vozzo]], _Sign choices for orientifolds_ ([arXiv:1905.06041](https://arxiv.org/abs/1905.06041)) <a href="https://ncatlab.org/nlab/revision/diff/orientifold/62">diff</a>, <a href="https://ncatlab.org/nlab/revision/orientifold/62">v62</a>, <a href="https://ncatlab.org/nlab/show/orientifold">current</a>

   added pointer to today’s

   • Pedram Hekmati, Michael Murray, Richard Szabo, Raymond Vozzo, Sign choices for orientifolds (arXiv:1905.06041)

   diff, v62, current

8. • CommentRowNumber8.
   • CommentAuthorUrs
   • CommentTimeMar 18th 2020
   • PermaLink
   Author: Urs
   Format: MarkdownItexI wrote a section ([here](https://ncatlab.org/nlab/show/orientifold#OrientifoldBackreactionOrNot)) on orientifold backreaction (or not), with some discussion of and quotes from the literature. <a href="https://ncatlab.org/nlab/revision/diff/orientifold/80">diff</a>, <a href="https://ncatlab.org/nlab/revision/orientifold/80">v80</a>, <a href="https://ncatlab.org/nlab/show/orientifold">current</a>

   I wrote a section (here) on orientifold backreaction (or not), with some discussion of and quotes from the literature.

   diff, v80, current

9. • CommentRowNumber9.
   • CommentAuthorUrs
   • CommentTimeSep 8th 2020
   • PermaLink
   Author: Urs
   Format: MarkdownItexadded pointer to: * [[Andreas Braun]], _M-Theory and Orientifolds_ ([arXiv1912.06072](https://arxiv.org/abs/1912.06072)) <a href="https://ncatlab.org/nlab/revision/diff/orientifold/86">diff</a>, <a href="https://ncatlab.org/nlab/revision/orientifold/86">v86</a>, <a href="https://ncatlab.org/nlab/show/orientifold">current</a>

   added pointer to:

   • Andreas Braun, M-Theory and Orientifolds (arXiv1912.06072)

   diff, v86, current

10. • CommentRowNumber10.
    • CommentAuthorUrs
    • CommentTimeSep 18th 2020
    • PermaLink
    Author: Urs
    Format: MarkdownItexadded publication data to: * [[Pedram Hekmati]], [[Michael Murray]], [[Richard Szabo]], [[Raymond Vozzo]], _Sign choices for orientifolds_, Commun. Math. Phys. 378, 1843–1873 (2020) ([arXiv:1905.06041](https://arxiv.org/abs/1905.06041)) <a href="https://ncatlab.org/nlab/revision/diff/orientifold/87">diff</a>, <a href="https://ncatlab.org/nlab/revision/orientifold/87">v87</a>, <a href="https://ncatlab.org/nlab/show/orientifold">current</a>

    added publication data to:

    • Pedram Hekmati, Michael Murray, Richard Szabo, Raymond Vozzo, Sign choices for orientifolds, Commun. Math. Phys. 378, 1843–1873 (2020) (arXiv:1905.06041)

    diff, v87, current

11. • CommentRowNumber11.
    • CommentAuthorperezl.alonso
    • CommentTimeOct 20th 2023
    • PermaLink
    Author: perezl.alonso
    Format: MarkdownItexBut isn't there a concrete definition as for [[orbifold]] in [[orbifold groupoid]]? Of the resources I've checked out (which are admittedly not many) they just "define" them in terms of what they're supposed to do.

    But isn’t there a concrete definition as for orbifold in orbifold groupoid? Of the resources I’ve checked out (which are admittedly not many) they just “define” them in terms of what they’re supposed to do.

12. • CommentRowNumber12.
    • CommentAuthorUrs
    • CommentTimeOct 20th 2023
    • PermaLink
    Author: Urs
    Format: MarkdownItexAbsolutely: If a direct $\mathbb{Z}/2$-factor in the equivariance group is singled out as on the bottom of [p. 32 here](https://arxiv.org/pdf/1909.12277.pdf#page=32) --- and if that $\mathbb{Z}/2$ acts by "Real involution" on whatever cohomology coeffcients one has--- then its fixed loci are the orientifolds.

    Absolutely: If a direct $\mathbb{Z}/2$-factor in the equivariance group is singled out as on the bottom of p. 32 here — and if that $\mathbb{Z}/2$ acts by “Real involution” on whatever cohomology coeffcients one has— then its fixed loci are the orientifolds.