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Note:These pages make extensive use of the latest XHTML and CSS Standards. They ought to look great in any standards-compliant modern browser. Unfortunately, they will probably look horrible in older browsers, like Netscape 4.x and IE 4.x. Moreover, many posts use MathML, which is, currently only supported in Mozilla. My best suggestion (and you will thank me when surfing an ever-increasing number of sites on the web which have been crafted to use the new standards) is to upgrade to the latest version of your browser. If that's not possible, consider moving to the Standards-compliant and open-source Mozilla browser.

March 26, 2004

User Experience

A few more blog-related notes.

  1. Srijith has discovered a minor security flaw in MovableType’s handling of email notifications.

    Update 3/27/2004: At Ben Trott’s request, Srijith has pulled the details of the flaw from his web site (apparently, Ben claims never to have received Srijith’s vulnerability report). Reluctantly, I’ve decided to follow suit here at Musings. Supposedly, the fix is in MT 3.0. If that (or a standalone patch) is released in a timely fashion, I’ll be happy about my decision. Otherwise, I may have to revisit it…

    Update 3/27/2004: Oh, to heck with it! We’re not going to have another Comment-Throttling fiasco. “All will be well when MT 3.0 comes out.” is not a viable Security Policy. The exploit is out there, and MT users need to know about it in order to protect themselves.

    In brief, if a spammer (or other miscreant) leaves a comment of the form

    Innocent comment here.
.
Spam links here.

    (that’s a single period on a line by itself) only the upper part will be sent in the notification email(s), while the full comment will be posted to your blog. If you are using Sendmail, you should patch your MT installation.

    --- lib/MT/Mail.pm.orig Wed Mar 24 19:55:40 2004
+++ lib/MT/Mail.pm      Wed Mar 24 19:58:06 2004
@@ -85,7 +85,7 @@
     local $SIG{ALRM} = sub { CORE::exit() };
     return unless defined $pid;
     if (!$pid) {
-        exec $sm_loc, "-t" or
+        exec $sm_loc, "-oi", "-t" or
             return $class->error(MT->translate(
                 "Exec of sendmail failed: [_1]", "$!" ));
     }

  2. My previous entry, as promised, uses SVG for figures. I’m curious as to how this works for various classes of users

    • Users with SVG-native builds of Mozilla
    • Users with the Adobe Plugin
    • Users with no SVG support in their browser (should fall back to a GIF image)

    Personally, I’m using the Adobe Plugin, and I find that scrolling past an SVG image, in Mozilla, is painfully slow. Safari doesn’t have this problem.

  3. My Atom feed is now “official.” My RSS 0.91 feed is deprecated (though not dropped … yet).

  4. Speaking of feeds and SVG figures, NetNewsWire is a little overzealous in dealing with the SVG figures in my full-content feeds (RSS 2.0 and Atom). I can see an Aggregator not wanting to deal with sorting out “good” <object> elements from “bad” ones, and instead just ignoring all <object> tags. But, just because you do that, why ignore the content of the <object> element? The content, in this case, is a GIF image, which is the fallback for those who can’t — or don’t wish to — deal with the SVG. NetNewsWire is perfectly happy displaying GIF images, but it doesn’t in this case, because the <img> element is ignored.

    I suppose I could strip out the <object> tags from my feed. But I don’t want to. Those whose client software (like NetNewsWire, ironically) is capable of handling an SVG figure ought to receive one.

Posted by distler at 12:01 AM | Permalink | Followups (8)

March 25, 2004

Fine-tuned

One-loop contribution to quartic Higgs coupling
Corrections to quartic Higgs self-coupling from stop and top loops.

We all learned on our grandfather’s knee that supersymmetry required a light Higgs. Back then, this was a cheering thought, for it meant that we would not have to wait too long for the Higgs to be discovered. The years passed, and the experimental lower bound on the mass of the Higgs crept slowly upwards. We now know that it must be heavier than 114 GeV or so.

Scott Thomas was in town the other week, and gave a very nice colloquium, explaining how serious the situation has become for the MSSM.

At tree level, m h<m Zcos(2 β) where tan(β)=〈H〉/〈H˜〉, and H & H˜ give masses, respectively, to the up and down type quarks. The inequality becomes an equality in the limit that the mass of one of the other neutral scalars in the Higgs sector, m A→∞.

With m Z=91 GeV, and m h>114 GeV, this bound is clearly violated. Fortunately, the one-loop corrections to the quartic self-coupling, depicted above tend to push this number up. m h 2 =m Z 2 cos 2 (2 β)+6 ∣λ t∣ 2 m t 2 4 π 2 log(m t˜/m t) Note that the supersymmetric cancellation between the two diagrams means that the result depends only logarithmically on the stop mass. To fit the current lower bound on m h, the stop must be heavy m t˜>850 GeV And each time we push up the lower bound on the Higgs mass, the lower bound on the stop mass goes up exponentially.

One-loop contribution to quadratic Higgs coupling
Corrections to the quadratic Higgs self-coupling dominated by stop loops.

While the corrections to the quartic terms in the Higgs potential depend only logarithmically on the stop mass, the corrections to the quadratic terms are proportional to m t˜ 2 . m 2 ∼∣μ∣ 2 −3 ∣λ t∣ 2 m t˜ 2 8 π 2 log(m t˜/M) where M is a messenger mass, at which the loop-momentum integral is effectively cut off. (It’s precisely these radiative corrections that drive this term negative, and lead to the electroweak symmetry-breaking.)

To end up with an electroweak symmetry-breaking scale around (100 GeV) 2 , one needs the μ parameter (the coefficient of HH˜ in the superpotential) to be in the TeV range, and its value must be tuned to within a few percent.

Personally, I can live with a fine-tuning in the 1% range. But you would not have to push the Higgs mass up too much further to make even me nervous.

Posted by distler at 12:30 AM | Permalink | Followups (11)