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Cold and Hot Dark Matter

  1. May 7, 2007 #1
    I will be writing my final exam tomorrow evening, and I am currently stuck on the following practice problem. It would be very nice if someone could help me out and I will remain eternally grateful for your help!

    1) (Multiple Choice) Which of the following statement(s) about Cold Dark Matter (CDM) is (are) incorrect:
    a) CDM particles travel at a speed much lower than c
    b) neutrinos are a candidate for CDM
    c) simulation models using CDM produce smaller scale structures than those using Hot Dark Matter
    d) CDM is likely baryonic
    e) CDM particles should be more massive than HOT Dark Matter particles

    Well, I believe that a and e are true, b and d are false, but I am totally unsure about c...is it true or false and why? Does anyone know?

    Thank you!:smile:
  2. jcsd
  3. May 7, 2007 #2
    Does anyone know whether c is true or false?

  4. May 7, 2007 #3


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    The option c is true because the more free-streaming (as for HDM) the more suppression of small scale fluctuations. You can read about it here.
  5. May 8, 2007 #4


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    a) is my guess. There was an article about this about a year ago:
    an excerpt:

    ". . .The speed is a big surprise. Current theory had predicted dark matter particles would be extremely cold, moving at a few millimetres per second; but these observations prove the particles must actually be quite warm (in cosmic terms) at 10,000 degrees. . . ."

    Still, much less than 'c' by any measure.
  6. May 8, 2007 #5
    What is Cold and Hot Dark Energy?
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