Does a closed right ideal of a C$^*$-algebra have a C$^*$-algebra?











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$A$ is an infinite dimensional C$^*$-algebra and $Jsubset A$ is a closed right ideal. $A$ and $J$ are infinite dimensional(as a vector space). I want to find an infinite dimensional C$^*$-algebra subset of $J$. How can I find it?



I know an infinite dimensional C$^*$-algebra has an infinite dimensional commutative C$^*$-subalgebra. So if $A_1$ is infinite dimensional commutative C$^*$-subalgebra of $A$, Is the set $A_1cap J$ an infinite dimensional C$^*$-algebra? If no, so what can I do?










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  • What is $I$ in your first paragraph?
    – Aweygan
    Nov 15 at 17:20










  • Execuse me for my mistake
    – Dadrahm
    Nov 15 at 17:29






  • 1




    No worries. Well in general if $J$ is a one-sided ideal, then $Jcap J^*$ is a two-sided ideal, hence a $C^*$-subalgebra, although I am not sure if there is any satisfying criteria for determining whether or not this ideal is infinite-dimensional, or even non-trivial.
    – Aweygan
    Nov 15 at 17:35












  • But if $J={ fin B(ell^2): f^*((1,0,0,0,ldots ))=0 } subseteq B(ell^2)$ then $Jcap J^* $ isn't an two sided ideal.
    – Dadrahm
    Nov 15 at 18:31

















up vote
1
down vote

favorite












$A$ is an infinite dimensional C$^*$-algebra and $Jsubset A$ is a closed right ideal. $A$ and $J$ are infinite dimensional(as a vector space). I want to find an infinite dimensional C$^*$-algebra subset of $J$. How can I find it?



I know an infinite dimensional C$^*$-algebra has an infinite dimensional commutative C$^*$-subalgebra. So if $A_1$ is infinite dimensional commutative C$^*$-subalgebra of $A$, Is the set $A_1cap J$ an infinite dimensional C$^*$-algebra? If no, so what can I do?










share|cite|improve this question
























  • What is $I$ in your first paragraph?
    – Aweygan
    Nov 15 at 17:20










  • Execuse me for my mistake
    – Dadrahm
    Nov 15 at 17:29






  • 1




    No worries. Well in general if $J$ is a one-sided ideal, then $Jcap J^*$ is a two-sided ideal, hence a $C^*$-subalgebra, although I am not sure if there is any satisfying criteria for determining whether or not this ideal is infinite-dimensional, or even non-trivial.
    – Aweygan
    Nov 15 at 17:35












  • But if $J={ fin B(ell^2): f^*((1,0,0,0,ldots ))=0 } subseteq B(ell^2)$ then $Jcap J^* $ isn't an two sided ideal.
    – Dadrahm
    Nov 15 at 18:31















up vote
1
down vote

favorite









up vote
1
down vote

favorite











$A$ is an infinite dimensional C$^*$-algebra and $Jsubset A$ is a closed right ideal. $A$ and $J$ are infinite dimensional(as a vector space). I want to find an infinite dimensional C$^*$-algebra subset of $J$. How can I find it?



I know an infinite dimensional C$^*$-algebra has an infinite dimensional commutative C$^*$-subalgebra. So if $A_1$ is infinite dimensional commutative C$^*$-subalgebra of $A$, Is the set $A_1cap J$ an infinite dimensional C$^*$-algebra? If no, so what can I do?










share|cite|improve this question















$A$ is an infinite dimensional C$^*$-algebra and $Jsubset A$ is a closed right ideal. $A$ and $J$ are infinite dimensional(as a vector space). I want to find an infinite dimensional C$^*$-algebra subset of $J$. How can I find it?



I know an infinite dimensional C$^*$-algebra has an infinite dimensional commutative C$^*$-subalgebra. So if $A_1$ is infinite dimensional commutative C$^*$-subalgebra of $A$, Is the set $A_1cap J$ an infinite dimensional C$^*$-algebra? If no, so what can I do?







functional-analysis ideals c-star-algebras






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edited Nov 16 at 6:21

























asked Nov 15 at 16:27









Dadrahm

3278




3278












  • What is $I$ in your first paragraph?
    – Aweygan
    Nov 15 at 17:20










  • Execuse me for my mistake
    – Dadrahm
    Nov 15 at 17:29






  • 1




    No worries. Well in general if $J$ is a one-sided ideal, then $Jcap J^*$ is a two-sided ideal, hence a $C^*$-subalgebra, although I am not sure if there is any satisfying criteria for determining whether or not this ideal is infinite-dimensional, or even non-trivial.
    – Aweygan
    Nov 15 at 17:35












  • But if $J={ fin B(ell^2): f^*((1,0,0,0,ldots ))=0 } subseteq B(ell^2)$ then $Jcap J^* $ isn't an two sided ideal.
    – Dadrahm
    Nov 15 at 18:31




















  • What is $I$ in your first paragraph?
    – Aweygan
    Nov 15 at 17:20










  • Execuse me for my mistake
    – Dadrahm
    Nov 15 at 17:29






  • 1




    No worries. Well in general if $J$ is a one-sided ideal, then $Jcap J^*$ is a two-sided ideal, hence a $C^*$-subalgebra, although I am not sure if there is any satisfying criteria for determining whether or not this ideal is infinite-dimensional, or even non-trivial.
    – Aweygan
    Nov 15 at 17:35












  • But if $J={ fin B(ell^2): f^*((1,0,0,0,ldots ))=0 } subseteq B(ell^2)$ then $Jcap J^* $ isn't an two sided ideal.
    – Dadrahm
    Nov 15 at 18:31


















What is $I$ in your first paragraph?
– Aweygan
Nov 15 at 17:20




What is $I$ in your first paragraph?
– Aweygan
Nov 15 at 17:20












Execuse me for my mistake
– Dadrahm
Nov 15 at 17:29




Execuse me for my mistake
– Dadrahm
Nov 15 at 17:29




1




1




No worries. Well in general if $J$ is a one-sided ideal, then $Jcap J^*$ is a two-sided ideal, hence a $C^*$-subalgebra, although I am not sure if there is any satisfying criteria for determining whether or not this ideal is infinite-dimensional, or even non-trivial.
– Aweygan
Nov 15 at 17:35






No worries. Well in general if $J$ is a one-sided ideal, then $Jcap J^*$ is a two-sided ideal, hence a $C^*$-subalgebra, although I am not sure if there is any satisfying criteria for determining whether or not this ideal is infinite-dimensional, or even non-trivial.
– Aweygan
Nov 15 at 17:35














But if $J={ fin B(ell^2): f^*((1,0,0,0,ldots ))=0 } subseteq B(ell^2)$ then $Jcap J^* $ isn't an two sided ideal.
– Dadrahm
Nov 15 at 18:31






But if $J={ fin B(ell^2): f^*((1,0,0,0,ldots ))=0 } subseteq B(ell^2)$ then $Jcap J^* $ isn't an two sided ideal.
– Dadrahm
Nov 15 at 18:31












1 Answer
1






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up vote
1
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You can't do that in general. Many C$^*$-algebras are simple. In such a case if $Bsubset J$ is a C$^*$-algebra, then
$$
B=Bcap B^*subset Jcap J^*={0},
$$

since $Jcap J^*$ is a closed ideal.






share|cite|improve this answer























  • Why $Jcap J^*=0$ ? $Jcap J^*$ is a two sided ideal of $J$ and not a two sided ideal of $A$, So why $Jcap J^*=0$
    – Dadrahm
    Nov 16 at 6:10












  • But if J is simple then $Jcap J^*=0$. Is there an infinite dimensional simple closed right ideal for ecah infinite dimensional $C^*$-algebra?
    – Dadrahm
    Nov 16 at 6:16












  • I don't really follow what you are saying; a right ideal is not an algebra, so what does "$J $ is simple" mean, and what would "ideal of $J $ mean? And, again, if $J $ is a right ideal of $A $, then $ J^*cap J $ is a bilateral ideal of $A $.
    – Martin Argerami
    Nov 16 at 12:49










  • Why $Jcap J^*$ is a two sided ideal of A?
    – Dadrahm
    Nov 16 at 12:51










  • a right ideal is not an algebra?! So I think I made some mistakes. Excuse me
    – Dadrahm
    Nov 16 at 12:53











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up vote
1
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You can't do that in general. Many C$^*$-algebras are simple. In such a case if $Bsubset J$ is a C$^*$-algebra, then
$$
B=Bcap B^*subset Jcap J^*={0},
$$

since $Jcap J^*$ is a closed ideal.






share|cite|improve this answer























  • Why $Jcap J^*=0$ ? $Jcap J^*$ is a two sided ideal of $J$ and not a two sided ideal of $A$, So why $Jcap J^*=0$
    – Dadrahm
    Nov 16 at 6:10












  • But if J is simple then $Jcap J^*=0$. Is there an infinite dimensional simple closed right ideal for ecah infinite dimensional $C^*$-algebra?
    – Dadrahm
    Nov 16 at 6:16












  • I don't really follow what you are saying; a right ideal is not an algebra, so what does "$J $ is simple" mean, and what would "ideal of $J $ mean? And, again, if $J $ is a right ideal of $A $, then $ J^*cap J $ is a bilateral ideal of $A $.
    – Martin Argerami
    Nov 16 at 12:49










  • Why $Jcap J^*$ is a two sided ideal of A?
    – Dadrahm
    Nov 16 at 12:51










  • a right ideal is not an algebra?! So I think I made some mistakes. Excuse me
    – Dadrahm
    Nov 16 at 12:53















up vote
1
down vote













You can't do that in general. Many C$^*$-algebras are simple. In such a case if $Bsubset J$ is a C$^*$-algebra, then
$$
B=Bcap B^*subset Jcap J^*={0},
$$

since $Jcap J^*$ is a closed ideal.






share|cite|improve this answer























  • Why $Jcap J^*=0$ ? $Jcap J^*$ is a two sided ideal of $J$ and not a two sided ideal of $A$, So why $Jcap J^*=0$
    – Dadrahm
    Nov 16 at 6:10












  • But if J is simple then $Jcap J^*=0$. Is there an infinite dimensional simple closed right ideal for ecah infinite dimensional $C^*$-algebra?
    – Dadrahm
    Nov 16 at 6:16












  • I don't really follow what you are saying; a right ideal is not an algebra, so what does "$J $ is simple" mean, and what would "ideal of $J $ mean? And, again, if $J $ is a right ideal of $A $, then $ J^*cap J $ is a bilateral ideal of $A $.
    – Martin Argerami
    Nov 16 at 12:49










  • Why $Jcap J^*$ is a two sided ideal of A?
    – Dadrahm
    Nov 16 at 12:51










  • a right ideal is not an algebra?! So I think I made some mistakes. Excuse me
    – Dadrahm
    Nov 16 at 12:53













up vote
1
down vote










up vote
1
down vote









You can't do that in general. Many C$^*$-algebras are simple. In such a case if $Bsubset J$ is a C$^*$-algebra, then
$$
B=Bcap B^*subset Jcap J^*={0},
$$

since $Jcap J^*$ is a closed ideal.






share|cite|improve this answer














You can't do that in general. Many C$^*$-algebras are simple. In such a case if $Bsubset J$ is a C$^*$-algebra, then
$$
B=Bcap B^*subset Jcap J^*={0},
$$

since $Jcap J^*$ is a closed ideal.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Nov 15 at 21:48

























answered Nov 15 at 20:53









Martin Argerami

121k1073172




121k1073172












  • Why $Jcap J^*=0$ ? $Jcap J^*$ is a two sided ideal of $J$ and not a two sided ideal of $A$, So why $Jcap J^*=0$
    – Dadrahm
    Nov 16 at 6:10












  • But if J is simple then $Jcap J^*=0$. Is there an infinite dimensional simple closed right ideal for ecah infinite dimensional $C^*$-algebra?
    – Dadrahm
    Nov 16 at 6:16












  • I don't really follow what you are saying; a right ideal is not an algebra, so what does "$J $ is simple" mean, and what would "ideal of $J $ mean? And, again, if $J $ is a right ideal of $A $, then $ J^*cap J $ is a bilateral ideal of $A $.
    – Martin Argerami
    Nov 16 at 12:49










  • Why $Jcap J^*$ is a two sided ideal of A?
    – Dadrahm
    Nov 16 at 12:51










  • a right ideal is not an algebra?! So I think I made some mistakes. Excuse me
    – Dadrahm
    Nov 16 at 12:53


















  • Why $Jcap J^*=0$ ? $Jcap J^*$ is a two sided ideal of $J$ and not a two sided ideal of $A$, So why $Jcap J^*=0$
    – Dadrahm
    Nov 16 at 6:10












  • But if J is simple then $Jcap J^*=0$. Is there an infinite dimensional simple closed right ideal for ecah infinite dimensional $C^*$-algebra?
    – Dadrahm
    Nov 16 at 6:16












  • I don't really follow what you are saying; a right ideal is not an algebra, so what does "$J $ is simple" mean, and what would "ideal of $J $ mean? And, again, if $J $ is a right ideal of $A $, then $ J^*cap J $ is a bilateral ideal of $A $.
    – Martin Argerami
    Nov 16 at 12:49










  • Why $Jcap J^*$ is a two sided ideal of A?
    – Dadrahm
    Nov 16 at 12:51










  • a right ideal is not an algebra?! So I think I made some mistakes. Excuse me
    – Dadrahm
    Nov 16 at 12:53
















Why $Jcap J^*=0$ ? $Jcap J^*$ is a two sided ideal of $J$ and not a two sided ideal of $A$, So why $Jcap J^*=0$
– Dadrahm
Nov 16 at 6:10






Why $Jcap J^*=0$ ? $Jcap J^*$ is a two sided ideal of $J$ and not a two sided ideal of $A$, So why $Jcap J^*=0$
– Dadrahm
Nov 16 at 6:10














But if J is simple then $Jcap J^*=0$. Is there an infinite dimensional simple closed right ideal for ecah infinite dimensional $C^*$-algebra?
– Dadrahm
Nov 16 at 6:16






But if J is simple then $Jcap J^*=0$. Is there an infinite dimensional simple closed right ideal for ecah infinite dimensional $C^*$-algebra?
– Dadrahm
Nov 16 at 6:16














I don't really follow what you are saying; a right ideal is not an algebra, so what does "$J $ is simple" mean, and what would "ideal of $J $ mean? And, again, if $J $ is a right ideal of $A $, then $ J^*cap J $ is a bilateral ideal of $A $.
– Martin Argerami
Nov 16 at 12:49




I don't really follow what you are saying; a right ideal is not an algebra, so what does "$J $ is simple" mean, and what would "ideal of $J $ mean? And, again, if $J $ is a right ideal of $A $, then $ J^*cap J $ is a bilateral ideal of $A $.
– Martin Argerami
Nov 16 at 12:49












Why $Jcap J^*$ is a two sided ideal of A?
– Dadrahm
Nov 16 at 12:51




Why $Jcap J^*$ is a two sided ideal of A?
– Dadrahm
Nov 16 at 12:51












a right ideal is not an algebra?! So I think I made some mistakes. Excuse me
– Dadrahm
Nov 16 at 12:53




a right ideal is not an algebra?! So I think I made some mistakes. Excuse me
– Dadrahm
Nov 16 at 12:53


















 

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